Space Weather

What Is Space Weather?

Activity on the Sun can cause space weather storms that affect us here on Earth. Solar storms can impact the technology we rely on everyday: Global Positioning Systems (GPS), satellites, and electric power grids. Just as with other types of weather, the National Weather Service forecasts space weather disturbances and serves as the official source for civilian alerts and warnings.

Space weather is a consequence of the behavior of the Sun, the nature of Earth’s magnetic field and atmosphere, and our location in the solar system.

There are various phenomena that originate from the Sun that can result in space weather storms. Outbursts from huge explosions on the Sun—Solar Flares and Coronal Mass Ejections (CME)—send space weather storms hurling outward through our solar system. The Sun also emits a continuous stream of radiation in the form of charged particles that make up the plasma of the solar wind.

The Sun

The Sun

Solar Flares

Solar Flares are huge explosions on the Sun. A flare appears as a sudden, intense brightening region on the Sun, typically lasting several minutes to hours. Flares are seen as bright areas on the Sun in optical wavelengths and as bursts of noise in radio wavelengths. The primary energy source of flares is the tearing and reconnection of strong magnetic fields. The electromagnetic emission produced during flares travels at the speed of light, taking about 8 minutes—rapidly affecting the day side of Earth.

An active region on the sun emitted a mid-level solar flare, peaking at 4:47 a.m. EST on Nov. 5, 2014. This is the second mid-level flare from the same active region, labeled AR 12205, which rotated over the left limb of the sun on Nov. 3. The image was captured by NASA's Solar Dynamics Observatory (SDO) in extreme ultraviolet light that was colorized in red and gold. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel. This flare is classified as an M7.9-class flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc. More information on NASA's SDO Mission. Image Credit: NASA/SDO

An active region on the sun emitted a mid-level solar flare, peaking at 4:47 a.m. EST on Nov. 5, 2014. This is the second mid-level flare from the same active region, labeled AR 12205, which rotated over the left limb of the sun on Nov. 3. The image was captured by NASA’s Solar Dynamics Observatory (SDO) in extreme ultraviolet light that was colorized in red and gold. This flare is classified as an M7.9-class flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc. Image Credit: NASA/SDO

Coronal Mas Ejections (CME)

Coronal Mas Ejections are explosive outbursts of plasma from the Sun’s outer atmosphere, the Corona. The blast of a CME typically carries roughly a billion tons of material outward from the Sun
at speeds as fast as hundreds of kilometers per second. A CME contains particle radiation (mostly protons and electrons) and powerful magnetic fields. In contrast to solar flares, CMEs are not particularly bright, may take hours to fully erupt from the Sun, and typically take 1-4 days to travel to Earth.

Solar Particle Events

Solar Particle Events release large numbers of high energy charged particles, predominately protons and electrons, which are accelerated to large fractions of the speed of light. These particles may arrive at Earth between 30 minutes and several hours.

Solar Particle Event

Solar energetic particles (SEP) are high-energy particles coming from the Sun consisting of protons, electrons, helium ions, and HZE ions. The fastest particles can reach speed up to 80% of the speed of light. Solar energetic particles can originate from two processes: energization at a solar-flare site or by shock waves associated with coronal mass ejections (CMEs).

Space Weather and the Solar Cycle

The number of sunspots on the surface of the Sun increases and decreases in solar cycles of approximately  11 years. Solar Minimum refers to the several years when the number of sunspots is lowest; Solar Maximum occurs in the years when sunspots are most numerous. The Sun is usually very active when sunspot counts are high, however, severe storms can occur anytime during the solar cycle. Sunspots show where the Sun’s magnetic field energy is building up and where it could release to cause solar flares and CMEs. The Sun gives off more radiation than usual during solar maximum. This extra energy creates changes in the Earth’s upper atmosphere.

Solar Cycle Prediction

The current prediction for Sunspot Cycle 24. Source:NASA


Sunspots are dark, cooler areas on the solar surface that contain strong, constantly shifting magnetic fields. A moderate-sized sunspot is many times larger than the size of the Earth. Sunspots form over periods lasting from days to weeks, and can persist for weeks and even months before erupting or dissipating. Sunspots occur when strong magnetic fields emerge through the solar surface and allow the area to cool slightly, from a background value of 6000°C down to about 4200°C. This cooler area appears as a dark spot on the Sun. As the Sun rotates, sunspots on its surface appear to move from left to right. It takes the Sun 27 days to make one complete rotation.


A gigantic sunspot – almost 80,000 miles across — can be seen on the lower center of the sun in this image from NASA’s Solar Dynamic Observatory captured on Oct. 23, 2014. This active region, named AR2192, is the largest of the current solar cycle. Ten Earth’s could be laid across its diameter. Credit: NASA/SDO

Impacts of Space Weather

Electric Power

Large currents in the ionosphere can induce currents in power lines. Surges from these induced currents can cause massive network failures and permanent damage to electric grid components.

Navigation Systems

Disturbances in the ionosphere can cause degradation in GPS range measurements and in severe circumstances, loss of lock by the receiver on the GPS signal.


Space weather storms can cause lost or degraded communications, radiation hazards to crew and passengers, unreliable navigational information, and problems with flight-critical electronic systems.

Human Space Exploration

Energetic particles present a health hazard to astronauts on space missions as well as threats to electronic systems. During space missions, astronauts outside spacecraft are less protected and more exposed to space radiation.

Satellite Operations

Highly energetic ions penetrate electronic components, causing bit-flips in a chain of electronic signals that can result in improper commands within the spacecraft or incorrect data from an instrument. Less energetic particles contribute to a variety of spacecraft surface charging problems, especially during periods of high geomagnetic activity.


Magnetic field changes associated with geomagnetic storms directly affect operations that use the Earth’s magnetic field for guidance, such as magnetic surveys, directional drilling, or the use of magnetic compasses. Ionospheric disturbances cause errors in location obtained from GPS signals.


Communications at all frequencies may be affected by space weather. High frequency (HF) radio communications are more routinely affected because this frequency band depends on reflection by the ionosphere to carry signals great distances.

Space Weather Storms

Radio Blackouts

Radio Blackouts are caused by bursts of X-ray and Extreme Ultra Violet radiation emitted from solar flares. Radio blackouts primarily affect High Frequency (HF) (3-30 MHz) communication, although fading and diminished reception may spill over to Very High Frequency (VHF) (30-300 MHz) and higher frequencies. These storms are a consequence of enhanced electron densities caused by solar flare emissions. The emissions ionize the sunlit side of Earth, which increases the amount of energy lost as radio waves pass through this region.

Radio blackouts are among the most common space weather events to affect Earth. Minor events occur, on average, 2000 times each solar cycle. Blackouts are by far the fastest to impact our planet. The
X-rays creating radio blackouts arrive at the speed of light–8 minutes from Sun to Earth, making advance warnings difficult. When flares occur, however, SWPC measures their intensity and forecasts their
duration. Usually the radio blackouts last for several minutes, but they can last for hours.

The impacts of Radio Blackouts are felt by industries relying on HF radio communication and low frequency signals, primarily the aviation and marine industries.

Solar Radiation Storms

Solar radiation storms occur when large quantities of charged particles, protons and electrons, are accelerated by processes at or near the Sun. When these processes occur, the near-Earth satellite environment is bathed with high energy particles. Earth’s magnetic field and atmosphere offer some protection from this radiation, but the amount of protection is a function of altitude, latitude, and magnetic field strength. The polar regions are most affected by energetic particles because the magnetic field lines at the poles extend vertically downwards, allowing the particles to spiral down the field lines and penetrate into the atmosphere, increasing ionization. Energetic protons reach Earth a half hour to several hours after a solar eruption. Solar radiation storms can last from a few hours to days, depending on the magnitude of the eruption. Solar radiation storms can occur at any time during the solar cycle but tend to be most common around solar maximum.

Solar radiation storm impacts include loss of HF radio communications through the polar regions, navigation position errors, elevated radiation exposure to astronauts, and to passengers and crew in aircraft at high altitudes and latitudes, and damage to satellite systems.

Geomagnetic Storms

Geomagnetic storms, strong disturbances to Earth’s magnetic field, pose problems for many activities, technological systems, and critical infrastructure. The Earth’s magnetic field changes in the course of a storm as the near-Earth system attempts to adjust to the jolt of energy from the Sun carried in the solar wind. CMEs and their effects can disturb the geomagnetic field for days at a time. The most visible attribute of a geomagnetic storm is the aurora, which becomes brighter and moves closer to the equator. This heightened aurora signals the vigorous electrodynamic processes at play as they respond to the burst of energy.

Aurora Borealis Over the Midwestern US

Aurora Borealis Over the Midwest. In this image taken on Jan. 25, 2012, the Aurora Borealis is seen from the International Space Station as it flew over the Midwest. Credit: NASA

Geomagnetic storms usually last a few hours to days. The strongest storms may persist for up to a week. A string of CMEs may cause prolonged disturbed periods related to the additional energy being pumped into Earth’s magnetic field. The frequency of geomagnetic storms, in general, depends on where we are in the solar cycle–with most storms occurring near solar maximum; however, these storms are also common in the declining phase due to high speed solar wind streams.

Geomagnetic storms induce currents that can have significant impact on electrical transmission equipment. Electric power companies have procedures in place to mitigate the impact of geomagnetic storms.

Current Space Weather

You can find reports of current space weather at  Select Space Weather from the menu.

Acknowledgements:  Information in this article was obtained from NASA and NOAA.

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How the Arctic Oscillation Influences Wisconsin Weather

The Arctic Oscillation is a climate pattern that influences winter weather in the Northern Hemisphere. It is defined by the pressure difference between air at mid-latitudes (around 45 degrees North, about the latitude of Montreal, Canada or Bordeaux, France) and air over the Arctic. A low-pressure air mass usually dominates the Arctic, and while higher pressure air sits over the mid-latitudes. This pressure difference generates winds that confine extremely cold air to the Arctic. Sometimes, the pressure systems weaken, decreasing the pressure difference between the Arctic and midlatitudes and allowing chilly Arctic air to slide south while warmer air creeps north. A weaker-than-normal Arctic Oscillation is said to be negative. When the pressure systems are strong, the Arctic Oscillation is positive.

Arctic Oscillation Phases

Positive and negative phases of the Arctic Oscillation

Meteorologists and climatologists who study the Arctic pay attention to the Arctic Oscillation, because its phase has an important effect on weather in northern locations. The positive phase of the Arctic Oscillation brings ocean storms farther north, making the weather wetter in Alaska, Scotland, and Scandinavia and drier in the western United States and the Mediterranean. The positive phase also keeps weather warmer than normal in the eastern United States, but makes Greenland colder than normal.

In the negative phase of the Arctic Oscillation the patterns are reversed. A strongly negative phase of the Arctic Oscillation brings warm weather to high latitudes, and cold, stormy weather to the more temperate regions where people live. Over most of the past century, the Arctic Oscillation alternated between its positive and negative phase. For a period during the 1970s to mid-1990s, the Arctic Oscillation tended to stay in its positive phase. However, since then it has again alternated between positive and negative, with a record negative phase in the winter of 2009-2010.

Arctic Oscillation, 2000 to Present

Arctic Oscillation from 2000 to Present

The Arctic Oscillation and Wisconsin

The Arctic Oscillation (AO) index describes the relative intensity of a semipermanent low-pressure center over the North Pole. A band of upper-level winds circulates around this center, forming a vortex. When the AO index is positive and the vortex intense, the winds tighten around the North Pole, locking cold air in place. This can result in a milder winter for Wisconsin. The weaker polar vortex of the negative phase allows cold air to plunge into Wisconsin and other parts of the midwestern United States.

In early 2013 a cold snap that extended into March was attributed to a negative phase of the AO. Of course, last winter a weak Polar Vortex added some cold to our weather.  For 2014-2015, it appears that the AO is trending toward a positive phase.  The National Weather Service used this factor, among others, in predicting a warmer and drier season.

The Arctic Oscillation in the Northern Hemisphere

As noted above, the AO will act with other major weather systems such as the Polar Vortex and El Nino/La Nina. Here is the influence of the AO as an isolated phenomenon:

Region AO Positive Phase AO Negative Phase
Eastern U.S. Above average temperatures Colder winters and an increase in nor’easters (coastal storms) for New England states
Western U.S. Warm, dry conditions Cooler weather
Canada & Greenland Below average temperatures Warmer in Western Greenland and Eastern Canada
Northern Europe & Asia Warmer and more precipitation, most notably in Scotland and Scandinavia More frigid temperatures
The Mediterranean Drought conditions Increased frequency of storms

The Arctic Oscillation is a result of natural variations within Earth’s atmosphere. Unlike other climate patterns which occur every so many years, the AO is always present and switches between its phases seemingly at random (science hasn’t yet discovered a pattern and there may not be one). For this reason, its episodes remain difficult to predict more than a few weeks in advance.

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Winter Awareness Week Declared for Nov. 10-14, 2014

Governor Scott Walker has declared November 10-14, 2014 as Winter Awareness Week in Wisconsin.

Winter 2013 In Greendale Wisconsin

Winter Scene in 2013, Greendale Wisconsin

The annual campaign, sponsored by Wisconsin Emergency Management (WEM), its ReadyWisconsin preparedness program and NOAA’s National Weather Service (NWS), is to remind people to be prepared for winter conditions that could threaten their safety.

“The number one thing to do: make sure you have an emergency supply kit in your car, it could save your life,” says Brian Satula, Wisconsin Emergency Management Administrator.

Winter storms are considered deceptive killers because most deaths are indirectly related to the storm.

For example, in the last five years Wisconsin has averaged 18,000 motor vehicle crashes during winter months. On average, 45 people are killed each year and more than 4700 injured on icy or snow-covered roads. Carbon monoxide poisoning is also a danger.

According to the Centers for Disease Control, carbon monoxide is the leading cause of accidental poisoning deaths in the United States, with more than 20,000 people visiting the emergency room and nearly 500 killed each year from overexposure to the gas.

Now is the time to winterize your car and home, gather items for an emergency kit in your car, and make sure you have a NOAA Weather Radio with fresh batteries. Additional winter weather tips and how to put together a winter emergency kit are available at the ReadyWisconsin website.

Residents also can sign up for a chance to win an emergency winter kit. The web address is In addition, there are numerous winter storm maps and a history of Wisconsin’s winter weather produced by the National Weather Service.

Total of All Winter Events

Total of All Winter Events

Yearly Average of All Winter Events

Yearly Average of All Winter Events

Total Number of Ice Storms

Total Number of Ice Storms

Total Number of Winter Storms

Total Number of Winter Storms

Normal Seasonal Snowfall fro Wisconsin

Normal Seasonal Snowfall for Wisconsin

Total Number of Blizzards

Total Number of Blizzards

Surviving Winter: Be Prepared

Some of the dangers associated with winter storms include loss of heat, power and telephone service and a shortage of supplies. To help protect your family, now is the time to put together a disaster supply kit. Here are some items to include:

  • Flashlights and extra batteries
  • Battery-powered NOAA Weather Radio and a commercial radio
  • Bottled water and non-perishable food that requires no cooking
  • First-aid supplies
  • Fire extinguisher, smoke detector and carbon monoxide detector
  • If appropriate, extra medications and baby items
  • If you have an emergency heating source such as a fireplace or space heater, make sure you have proper ventilation
  • Make sure pets have shelter and plenty of food and water

Use caution when using alternative heating sources such as space heaters.

  • Keep anything flammable at least three feet away from heating equipment.
  • Make sure portable electric space heaters have an automatic shut-off.
  • Space heaters need constant watching. Never leave a space heater on when you leave a room or go to sleep. Never place a space heater close to any sleeping person.
  • Make sure all cords on electric heaters are plugged directly into wall outlet (don’t use an extension cord) and check cord for any frays or breaks in the insulation surrounding the wires.
  • Check the cord and outlet occasionally for overheating; if it feels hot, discontinue use.
  • Place the heater on a level, hard and nonflammable surface, not on rugs or carpets or near bedding or drapes.
  • Use a heater that has been tested to the latest safety standards and certified by a nationally recognized testing laboratory. These heaters will have the most up to date safety features; older space heaters may not meet the newer safety standards.

Winter Driving in Wisconsin

It is important for all of us to prepare for the power of winter storms. Here are some more winter facts:

  • In the last five years Wisconsin has averaged 18,000 motor vehicle crashes during the winter months when roads are covered with ice, snow or slush.
  • On average, 45 people are killed and 4,700 injured in Wisconsin each winter season in accidents when roads are covered in ice, snow and slush.
  • Many crashes are caused by “driving too fast for current conditions.” Also, when the first blast of winter arrives, motorists often need to “re-learn” how to drive in slippery conditions.
  • Heavy rains and melted snow in late winter or early spring can result in flooded roads. Turn Around—Don’t Drown™! (Turn Around Don’t Drown™ is a NOAA National Weather Service campaign to warn people of the hazards of walking or driving a vehicle through flood waters)

Winter Driving HazardsPlan your travels and check the latest weather reports to avoid a winter storm. You can find out the latest road conditions by visiting the Wisconsin Department of Transportation travel information website at or by calling 511.

It is also important to check and winterize your vehicles before the winter season begins. Keep your gas tank near full to avoid ice in the tank and fuel lines. Make sure your car’s battery is in good shape – cold temperatures can reduce the effectiveness of a battery by 50 percent.

If expecting adverse weather during your trip, tell someone at both ends of your journey where you are going and the route you intend to take. Report your safe arrival. Make certain that both parties have your cell phone number and license plate number before you start your trip.

Here are some Driving tips:

  • Be gentle with both the accelerator and brake.
  • Don’t use cruise control in wintery conditions.
  • Don’t be overconfident in your four-wheel drive vehicle.
  • You may get going quicker than others but you can’t stop faster. Four-wheel drive vehicles can lose traction as quickly as two-wheel drive.

Carry emergency supplies in your car just in case:

  • Carry a winter storm survival kit in the back seat of your vehicle (in case your trunk jams or is frozen shut) that includes:
  • Blankets or sleeping bags
  • Flashlight with extra batteries
  • First-aid kit
  • Shovel, tools, booster cables and windshield scraper
  • High-calorie non-perishable food (raisins, candy bars, energy/protein bars, etc.)
  • Sand or cat litter to use for traction
  • Cell phone adapter
Current Road Conditions for the Midwest

Current Road Conditions for the Midwest

Safety First – Stay Informed

The National Weather Service (NWS) issues winter storm warnings and watches. Here’s what they mean and what you should do.

Winter Storm Watch – Winter storm conditions (heavy snow, sleet and freezing rain) are possible within the next 36-48 hours. Continue monitoring the weather forecast.

Winter Storm or Ice Storm Warning – A significant winter event is occurring or will begin in the next 24 hours. The combination of snow, sleet, freezing rain and moderate winds will impact travel and outdoor activities. An Ice Storm Warning is issued when mostly freezing rain is expected with ice accumulations of 1/4 inch or more within a 12-hour period. Take necessary precautions – consider canceling travel plans.

Blizzard Warning – A dangerous event with winds that are 35 mph or greater in combination with falling and/or blowing snow that reduces visibility to 1/4 mile or less for a duration of at least 3 hours.

What is possible? Residents can expect almost anything, ranging from killer dense fog and flooding rains to widespread heavy snows and blizzards that can isolate a village/city for days. The only month without a tornado in Wisconsin’s history is February! Be ready!

Wisconsin Winter Weather Facts – National Weather Service

  • The coldest temperature in the winter of 2013-14 was -38 at Ladysmith (Rusk County) on December 31, 2013.
  • Upson (Iron County) had the most snow with 171.1 inches in the 2013-14 winter season, while Juneau (Dodge County) had the least with only 33.6 inches. Most of the central and southern counties had 50 to 70 inches which was well above normal.
  • Wisconsin’s all-time, lowest temperature is -55°F on February 2 & 4, 1996, near Couderay (Sawyer Co.). Readings of -30°F or colder have been recorded in every month from November through April. Of course, brief readings in the 50’s, 60’s and 70’s are possible during winter as well!
  • Average annual snowfall ranges from 32 to 40 inches near the Illinois border to 135 to 168 inches in the Iron County snow-belt from Gurney to Hurley. The extremes are 31.9 inches in Beloit, Rock County to 167.5 inches in Hurley, Iron County, for the period of 1981-2010.

Official snowfall records

  • Greatest daily total – Pell Lake, 26 inches of snow on Feb. 2, 2011 and Neillsville, 26 inches on December 27, 1904.
  • Greatest single storm total – Superior, 31.0 inches over Oct. 31-Nov. 2, 1991.
  • Greatest monthly total – Hurley, 103.5 inches in Jan. 1997.
  • Greatest seasonal total – Hurley, 301.8 inches in winter of 1996-97.
  • Deepest snow on ground (excluding drifts) – Hurley, 60 inches on Jan. 30, 1996.

Keep Warm and Safe

Frostbite is damage to body tissue caused by extreme cold. A wind chill around –20°F could cause frostbite in just 15 minutes or less. Frostbite causes a loss of feeling and a white or pale appearance in extremities such as fingers, toes, ear tips or the tip of the nose. If symptoms are detected, seek medical care immediately!

Hypothermia is a condition that develops when the body temperature drops below 95°F. It is very deadly. Warning signs include uncontrollable shivering, disorientation, slurred speech and drowsiness. Seek medical care immediately!

Overexertion is dangerous. Cold weather puts an added strain on the heart. Unaccustomed exercise such as shoveling snow or pushing a car can bring on a heart attack or make an existing medical condition worse.

Pets also need extra care when the temperatures fall. They should be brought inside when the temperature reaches 30°F with wind chill. Dogs and cats can get frost bitten ears, nose and feet if left outside during bitter cold weather. Chemicals used to melt snow and ice can also irritate pets’ paws – be sure to keep anti-freeze, salt and other poisons away from pets.

More Information

Winter StormsClick on the image above for an informative brochure about winter safety preparedness.

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El Niño and Its Impact On Our Weather

El Niño and La Niña are opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific (approximately between the International Date Line and 120 degrees West).

La Niña is sometimes referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO. These deviations from normal surface temperatures can have large-scale impacts not only on ocean processes, but also on global weather and climate.

El Niño and La Niña episodes typically last nine to 12 months, but some prolonged events may last for years. They often begin to form between June and August, reach peak strength between December and April, and then decay between May and July of the following year. While their periodicity can be quite irregular, El Niño and La Niña events occur about every three to five years. Typically, El Niño occurs more frequently than La Niña.

El Niño Phenomenon

This diagram shows the El Niño phenomenon. Observations have shown that the frequency and intensity of El Niño and la Nina has increased.

El Niño

El Niño means The Little Boy, or Christ Child in Spanish. El Niño was originally recognized by fishermen off the coast of South America in the 1600s, with the appearance of unusually warm water in the Pacific Ocean. The name was chosen based on the time of year (around December) during which these warm waters events tended to occur.

The term El Niño refers to the large-scale ocean-atmosphere climate interaction linked to a periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific.

Typical El Niño effects are likely to develop over North America during the upcoming winter season. Those include warmer-than-average temperatures over western and central Canada, and over the western and northern United States. Wetter-than-average conditions are likely over portions of the U.S. Gulf Coast and Florida, while drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest.

La Niña

La Niña means The Little Girl in Spanish. La Niña is also sometimes called El Viejo, anti-El Niño, or simply “a cold event.”

La Niña episodes represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific. Global climate La Niña impacts tend to be opposite those of El Niño impacts. In the tropics, ocean temperature variations in La Niña also tend to be opposite those of El Niño.

During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.

Current Sea Surface TemperatureSea surface temperature in the equatorial Pacific Ocean (above). El Niño is characterized by unusually warm temperatures and La Niña by unusually cool temperatures in the equatorial Pacific. Anomalies (below) represent deviations from normal temperature values, with unusually warm temperatures shown in red and unusually cold anomalies shown in blue.

Current Sea Surface Temperature Anomalies

To filter out month-to-month variability, average sea surface temperature in the Niño 3.4 region is calculated for each month, and then averaged with values from the previous month and following month. This running three-month average value is compared with average sea surface temperature for the same three months during 1971 – 2000. The departure from the 30-year average of the three-month average is known as the Oceanic Niño Index or ONI.SST AnamolyENSO Conditions

For real-time monitoring and prediction, NOAA considers El Niño conditions to be present when the Oceanic Niño Index is at least +0.5. In other words, El Niño conditions exist when the three-month average sea surface temperature in the Niño 3.4 region is at least 0.5°C warmer than average.

Conversely, NOAA declares that La Niña conditions exist when the Oceanic Niño Index is less than -0.5. This means that the three-month sea surface temperature in the Niño 3.4 region is at least 0.5°C cooler than average.

Whenever the Oceanic Niño Index is between +0.5 and -0.5, conditions are ENSO-neutral. A table of ONI values for each three-month period from 1950 to present is available from NOAA’s Climate Prediction Center.

El Niño and Its Impact on the United States

By examining seasonal climate conditions in previous El Niño years, scientists have identified a set of typical impacts associated with the phenomenon. Associated with doesn’t mean that all of these impacts happen during every El Niño episode. However, they happen more often during El Niño than you’d expect by chance, and many of them have occurred during many El Niño events.

ENSO Impact on United States

Average location of the Pacific and Polar Jet Streams and typical temperature and precipitation impacts during the winter over North America. Map by Fiona Martin for NOAA

In general, El Niño-related temperature and precipitation impacts across the United States occur during the cold half of the year (October through March). The most reliable of these signals (the one that has been observed most frequently) is wetter-than-average conditions along the Gulf Coast from Texas to Florida during this 6-month period. This relationship has occurred during more than 80% of the El Niño events in the past 100 years.

El Niño and Southeastern Wisconsin in 2015

These events can alter wind and weather patterns thousands of miles away. For us, El Niño brings a greater chance of warmer than normal temperatures with less snow over winter. As we approach the end of 2014 and are looking towards Winter weather in early 2015, it appears that there will probably be at least a weak El Niño effect.  This does not necessarily mean warmer weather and less snow are a certainty as other weather phenomena can overshadow El Niño.

Recent strong El Niño events have been associated with the following impacts on weather in the Milwaukee area:

Ell Nino and Milwaukee

What El Niño Means for Southern Wisconsin. Source: NWS Milwaukee/Sullivan Office

As indicated, we are on track for a weak El Niño event.  A weaker El Niño would be expected to have a lesser effect on temperature and precipitation and right now it looks like an equal chance of it providing us with a warmer or a cooler winter.

Source: NOAA National Ocean Service.

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A Polar Vortex in 2015?

When temperatures plunged into the sub-zero range for much of the country in early 2014, the term “polar vortex” became a household expression. The Polar Vortex is not a new phenomenon. The polar vortex was first described as early as the mid-nineteenth century.

The polar vortex is an area of low pressure—a wide expanse of swirling cold air—that is parked in polar regions. For North America, the one in the Arctic has the greatest impact on weather patterns. The air within the Northern Hemisphere polar vortex is referred to as polar air or Arctic air, depending on temperature, with the Arctic air being the coldest. South of the polar vortex, the atmosphere is much warmer, representing sub-tropical air, and, further south, tropical air. The boundary between the cold air within the vortex and the warmer air to the south is a region of sharp horizontal gradients in temperature, with temperatures decreasing to the north. These sharp temperature gradients give rise to the polar front jet stream, a fairly narrow ribbon of especially fast-moving air, flowing broadly from west to east. Hence, the southern boundary of the polar vortex essentially corresponds to the location of the polar front jet stream.

Sometimes this low-pressure system, full of cold Arctic air, strays a little bit too far from home. Part of it can break off and migrate southward, bringing all of that cold air with it. Just like that, areas as far south as Florida get to experience their own little taste of life in the Arctic.

MILWAUKEE, WI – JANUARY 7: A man braves the cold and walks along the shore of Lake Michigan as temperatures remain in the negative digits on January 7, 2014 in Milwaukee, Wisconsin. A ‘polar vortex’ of frigid air centered on the North Pole dropped temperatures to the negative double digits at its worst. (Photo by Darren Hauck/Getty Images)

We actually want a strong polar vortex to stay warm?

The breaking off of part of the vortex is what defines a polar vortex event. But it actually occurs when the vortex is weaker, not stronger. That might sound weird—but it actually makes sense. Normally, when the vortex is strong and healthy, it helps keep a current of air known as the jet stream traveling around the globe in a pretty circular path. This current keeps the cold air up north and the warm air down south.

Polar Vortex

This pair of images compares the boundaries of the polar vortex. The left image plots the height of the 500 millibar surface, about halfway up in the atmosphere, averaged for all Januarys over the period 1981-2010. The right image maps the 500 millibar height surface averaged for 1-5 January 2014. The shape of the polar vortex is quite different. The polar vortex is defined by the blue and purple colors poleward of the yellow colors, separating the polar and Arctic air and from warmer air to the south. The boundary of the polar vortex is where the yellow transitions to the green, and the tightly packed lines indicate a strong horizontal temperature gradient and define the jet stream. The air within in the jet stream, and within the vortex as a whole, rotates from west to east like a big whirlpool. Note the meanders in the vortex—these are the longwave ridges and troughs. This period saw a very strong Arctic outbreak over the central United States linked to a strong longwave trough moving into the area. Credit: M. Serreze, NSIDC

But without that strong low-pressure system, the jet stream doesn’t have much to keep it in line. It becomes wavy and rambling. Put a couple of areas of high-pressure systems in its way, and all of a sudden you have a river of cold air being pushed down south along with the rest of the polar vortex system.

That’s what happened in early 2014. The polar vortex suddenly weakened, and a huge high-pressure system formed over Greenland. The high-pressure system blocked the escape of all that cold air in the jet stream, and allowed part of the polar vortex to break off and move southward. Places as far south as Tampa, Florida experienced the wrath of this wandering polar vortex. Most of Canada and parts of the Midwestern United States had temperatures colder than Alaska at the height of this cold snap!

It’s important to remember that not all cold weather is the result of the polar vortex. While the polar vortex is always hanging out up north, it normally minds its own business. It takes pretty unusual conditions for it to weaken or for it to migrate far south, and other things can cause cold arctic air to travel our way, too.

The Polar Vortex in 2015

From the discussion above, it should be clear that there is always a polar vortex. The real question is to what extent will the polar vortex meander? The answer to this question is not an easy one. The farther in advance a weather prediction is made, the less accurate it will be.  Forecasts of a few days in advance are usually accurate.  Such a long range forecast is based more on the “art” of forecasting than on the science. That is not to say that this long range forecasting ignores science – it’s just that the current state of weather science does not support accurate long range forecasts.

The answer to whether or not the polar vortex meandering will bring us extremes in col weather is – maybe. Not an entirely satisfying answer, but the best answer that can be given at this time. There is some difference of opinion among the major forecasters on this, however.

AccuWeather predicts the return of the polar vortex, at least for the Northeast portion of the country, with the South also experiencing cold temperatures.

The Weather Channel is also calling for a return of the polar vortex.

The National Weather Service released their long-range forecast which calls for a warmer-than-average west and cooler- and wetter-than-average south.  The return of the polar vortex was seen as less likely.

The differences in these forecasts result from emphasis on different weather elements at play.  These include such factors as the state of snowfall levels in Siberia, the state of the El Nino pattern, and the phase of the Arctic Oscillation, among others.

One thing we do know and that is that Wisconsin winters bring their share of cold weather and it won’t be long until tho uncertain long range winter forecasts give way to actual winter weather and more accurate short term forecasts.

Acknowledgement is made to the National Weather Service and National Snow & Ice Data Center for material used in this article.

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Changes to Storm Prediction Center Outlooks Effective Today

To better communicate the risk of severe weather, outlooks issued by the NOAA National Weather Service Storm Prediction Center will add two new categories effective today. The change is being made to better describe the likelihood of severe weather, and bring better consistency to the risks communicated in the short and medium range forecasts for the nation.

The SPC’s Day 1, Day 2 and Day 3 severe weather outlook categories will change from the current four (see text, slight, moderate, high), to five: marginal, slight, enhanced, moderate and high. The marginal category will replace see text, and the enhanced category will indicate risk levels at the upper end of a slight, but below a moderate. In addition to the words, numbers and colors will be used to convey the threat.

The changes are being made based on feedback from customers. As the NWS continues its efforts to evolve into an organization of the 21st century, this information will better prepare decision makers.

“This change is part of the National Weather Service’s efforts to build a Weather-Ready Nation,” said SPC Director Russell Schneider. “It reflects our increased ability to forecast hazardous severe weather and advances our ability to communicate hazardous weather risk to the public.”

With these changes, the probabilistic information that has long been available and used by professional meteorologists will now be better represented in the graphical information most frequently used by the public. The format changes will also improve the use of SPC severe weather forecasts for customers who incorporate SPC outlooks into GIS systems.

For More Information

Experimental SPC Day 1, 2, 3 Convective Outlook Change Page

SPC Proposed Sever Weather Outlook Graphic

An example of a Public Severe Weather Outlook graphic.

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The Jet Stream

As the seasons of colder weather begin in Southeastern Wisconsin, many weather reports will begin to place more emphasis on the Jet Stream. Jet streams are like rivers of wind high above in the atmosphere. These slim strips of strong winds have a huge influence on climate, as they can push air masses around and affect weather patterns.

The jet streams typically run from west to east, and their width is relatively narrow compared to their length. Jet streams are typically active at about 7 miles (11 kilometers) above the Earth’s surface and travel near the altitude of the tropopause, the transition between the troposphere and the stratosphere.

Jet streams are caused by a combination of a planet’s rotation on its axis and atmospheric heating by solar radiation. Jet streams form near boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air towards the equator. Because air temperature influences jet streams, they are more active in the winter when there are wider ranges of temperatures between the competing Arctic and tropic air masses.

The Jet Stream

The Jet Stream

The actual appearance of jet streams result from the complex interaction between many variables – such as the location of high and low pressure systems, warm and cold air, and seasonal changes. They meander around the globe, dipping and rising in altitude/latitude, splitting at times and forming eddies, and even disappearing altogether to appear somewhere else.

Jet streams also “follow the sun” in that as the sun’s elevation increases each day in the spring, the average latitude of the jet stream shifts poleward. (By Summer in the Northern Hemisphere, it is typically found near the U.S. Canadian border.) As Autumn approaches and the sun’s elevation decreases, the jet stream’s average latitude moves toward the equator.

Also, the jet stream is often indicated by a line on maps and by television meteorologist. The line generally points to the location of the strongest wind. Jet streams are typically wider and not as distinct but a region where the wind increase toward a core of strongest wind.

One way of visualizing this is to consider a river. The river’s current is generally the strongest in the center with decreasing strength as one approaches the river’s bank. It can be said that jet streams are “rivers of air”.

Weather forecasters have an interest in the jet streams because they play an important role in determining the weather as they usually separate colder air and warmer air. Jet streams are one of the forces that push air masses around, moving weather systems to new areas. Jet streams don’t usually follow a straight path — they travel in patterns called peaks and troughs and they shift. Predicting these shifts is a major challenge for meteorologists.

USA Jet Stream Forecast Maps for Next 3-Days

Click on any image to enlarge it. Jet stream forecasts are courtesy of the University Corporation of Atmospheric Research (UCAR).

Current Jet Stream
Tomorrow’s Jet Stream Forecast
Loop of Jet Stream next 3- Days (NAM)
Today’s Jet Stream Forecast
Day- 3 Jet Stream Forecast
Loop of Jet Stream next 7-Days (GFS)
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Winter Outlook for 2014-2015

NOAA just released its 2014-2015 Winter Outlook. What does this mean for Southeastern Wisconsin? In the following video, meteorologist Mike Halpert from the National Weather Service Climate Prediction Center breaks down the seasonal climate outlook for this upcoming winter.

Below average temperatures are favored in parts of the south-central and southeastern United States, while above-average temperatures are most likely in the western U.S., Alaska, Hawaii and New England.

Outlook Map Temperatures 2014F

Credit: NOAA

While drought may improve in some portions of the U.S. this winter, California’s record-setting drought will likely persist or intensify in large parts of the state.

The Precipitation Outlook favors above-average precipitation across the southern tier, from the southern half of California, across the Southwest, South-central, and Gulf Coast states, Florida, and along the eastern seaboard to Maine. Above-average precipitation also is favored in southern Alaska and the Alaskan panhandle. Below-average precipitation is favored in Hawaii, the Pacific Northwest and the Midwest.

Outlook Map Precipitation 214F

Credit: NOAA

Last year’s winter was exceptionally cold and snowy across most of the United States, east of the Rockies. A repeat of this extreme pattern is unlikely this year, although the Outlook does favor below-average temperatures in the south-central and southeastern states.

In addition, the Temperature Outlook favors warmer-than-average temperatures in the Western U.S., extending from the west coast through most of the inter-mountain west and across the U.S.-Canadian border through New York and New England, as well as Alaska and Hawaii.

The U.S. Seasonal Drought Outlook, updated today and valid through January, predicts drought removal or improvement in portions of California, the Central and Southern Plains, the desert Southwest, and portions of New York, Connecticut, Rhode Island and Massachusetts. Drought is likely to persist or intensify in portions of California, Nevada, Utah, Idaho, Oregon and Washington state. New drought development is likely in northeast Oregon, eastern Washington state, and small portions of Idaho and western Montana.

This seasonal outlook does not project where and when snowstorms may hit or provide total seasonal snowfall accumulations. Snow forecasts are dependent upon the strength and track of winter storms, which are generally not predictable more than a week in advance.

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Lunar Eclipses

A Lunar eclipse occurs when the Sun casts Earth’s shadow onto the Moon. For this to happen, the Earth must be physically between the Sun and Moon with all three bodies lying on the same plane of orbit. A lunar eclipse can only occur during a Full Moon and when the Moon passes through all or a portion of Earth’s shadow.

Geometry of a Lunar Eclipse

Schematic diagram of the shadow cast by the Earth. Within the central umbra shadow, the Moon is totally shielded from direct illumination by the Sun. In contrast, within the penumbra shadow, only a portion of sunlight is blocked.

The outer portion of the shadow cast from Earth is known as the penumbral shadow, which is an area where Earth obstructs only a part of the Sun’s light from reaching the Moon.  The umbral shadow is the “inner” shadow, which is the area where Earth blocks all direct sunlight from reaching the Moon.  A penumbral lunar eclipse is subtle and very difficult to observe.  A partial lunar eclipse is when a portion of the Moon passes through the Earth’s umbral shadow.  Finally, a total lunar eclipse is when the entire Moon passes into the Earth’s umbral shadow.  During a total lunar eclipse, the sequence of eclipses are penumbral, partial, total, partial and back to penumbral.

Unlike solar eclipses, a total lunar eclipse lasts a few hours, with totality itself usually averaging anywhere from about 30 minutes to over an hour.  This is due to the large relative size of Earth over the Moon (the Moon’s diameter is only about 2150 miles), therefore casting a large umbral shadow on the Moon.  In addition, lunar eclipses are more frequent than their solar counterparts.  There are zero to three lunar eclipses per year (although possibly not all at the same location on Earth) where the Moon passes through at least a portion of the Earth’s umbral shadow (producing a partial to total eclipse).  As stated above in the solar eclipse explanation, the Moon’s orbit is tilted 5 degrees from Earth’s orbit.  For an eclipse to occur, the Moon and Earth have to be on the same orbital plane with the Sun, so the Earth’s shadow can be cast onto the Moon from the Sun.  This is why lunar eclipses only occur on average one or two times a year instead of every month.

Even though the Moon is immersed in the Earth’s umbral shadow, indirect sunlight will still reach the Moon thus illuminating it slightly.  This is because indirect sunlight reaches the Moon and also the Earth’s atmosphere will bend a very small portion of sunlight onto the Moon’s surface.  Many times during lunar totality, the color of the Moon will take on a dark red hue or brown/orange color.  As sunlight passes through Earth’s atmosphere, the blue-light is scattered out.  The amount of illumination of the Moon will vary depending on how much dust is in the Earth’s atmosphere.  The more dust present in the atmosphere, the less illuminated the Moon will be.

Lunar eclipses are safe to be viewed by the naked eye, through binoculars or a telescope.  Below is a table which shows partial and total lunar eclipses visible in the United States.









3 hrs 20 min

 0 hrs 59 min 

5:54 AM CDT


 All Eclipse Visible for  Western U.S.


3 hrs 29 min

0 hrs 5 min

7:00 AM CDT


Eclipse ongoing at Sunrise/Moonset


3 hrs 20 min

1 hr 12 min

9:47 PM CDT


All Eclipse Visible East of Rockies


3 hrs 23 min

1 hr 16 min

7:30 AM CST


Eclipse ongoing at Moonset


3 hrs 17 min

1 hr 02 min

11:12 PM CST


All Eclipse Visible for U.S.


3 hrs 7 min

0 hrs 15 min

6:19 AM CDT


Eclipse ongoing at Sunrise/Moonset


3 hrs 28 min

3:03 AM CST


Partial Eclipse ( but near total)  All Visible for U.S.


3 hrs 27 min

1 hr 25 min

11:11 PM CDT


Except for Far Pacific NW, All Eclipse Visible


3 hrs 40 min

1 hr 25 min

4:59 AM CST


Eclipse ongoing at Moonset for East Coast, otherwise All Eclipse Visible


1 hr 03 min

9:44 PM CDT


Partial Eclipse, very little of Moon obscured


3 hrs 38 min

1 hr 05 min

1:59 AM CDT


All Eclipse Visible for U.S.


3 hrs 27 min

0 hrs 58 min

5:34 AM CST


Eclipse ongoing at Moonset/Sunrise for eastern U.S.


3 hrs 18 min

11:13PM CDT


Partial Eclipse (but near total), All Visible for U.S.


0 hrs 56 min

10:13 PM CST


Partial Eclipse, very little of Moon obscured


3 hrs 40 min

1 hr 42 min

10:22 PM CDT


Eclipse ongoing at Moonrise for western U.S.


3 hrs 33 min

00 hr 54 min

4:42 PM CST


Eclipse ongoing at Moonrise


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Autumn, Frost, and Indian Summer in Wisconsin

The leaves are falling from the trees and the temperatures are trending lower. It’s fall in Wisconsin.  For some of us, the first frost has already occurred.  The rest of us will have the experience in the near future.  The good news is that the first frost heralds a time commonly known as Indian Summer.  This is our last respite before Winter.


Frost is the term for several types of coatings or deposits of ice that may form in humid air in cold conditions, usually overnight. In temperate climates such as that of Wisconsin, it most commonly appears as fragile white crystals or frozen dew drops near the ground. In colder climates it occurs in a greater variety of forms.

Frost on the Grass

Fall Frost on the Grass

The definition from the National Weather Service is: Frost describes the formation of thin ice crystals on the ground or other surfaces in the form of scales, needles, feathers, or fans. Frost develops under conditions similar to dew, except the temperatures of the Earth’s surface and earthbound objects falls below 32°F. As with the term “freeze,” this condition is primarily significant during the growing season. If a frost period is sufficiently severe to end the growing season or delay its beginning, it is commonly referred to as a “killing frost.” Because frost is primarily an event that occurs as the result of radiational cooling, it frequently occurs with a thermometer level temperature in the mid-30s.

Frost may damage crops or reduce future crop yields, so farmers in frost-prone regions may spend a great deal of money on measures to prevent it forming.  For they typical gardener, frost signals the end of the outdoor growing season.

According to Wendell Bechtold, a meteorologist with the National Weather Service Forecast Office in St. Louis, MO, “Frost formation is a complex process, and conditions have to be “right” for it to occur. Frost forms on surfaces directly from the vapor state, without condensing as dew. If dew forms, frost formation is unlikely, even if the temperature drops below freezing.

Frost is more likely to form on surfaces above the ground first, such as house roofs, or automobiles, because the air immediately above the ground is usually a few degrees warmer than air a few feet higher. There is some heat transfer from the ground to the air a few centimeters above it. If there is much wind, frost will not form either. (Neither will dew, as both these occurrences require little or no wind, so the atmosphere will not stay mixed.) If the skies are cloudy, usually dew or frost will not form either, as the clouds reflect the radiated heat from the ground, which helps in keeping the lower layers mixed.

So the ideal conditions for frost formation is a night with clear skies, light winds, and a temperature forecast to be near or a little below freezing. Standard temperature measurements are taken from about 2 meters above ground. On a calm night the ground temperature can be as much as 5-7 degrees cooler than the standard temperature reading. If there is some wind, the air stays mixed, and the temperature difference disappears.”

The first frost in Wisconsin usually occurs in the months of September and October depending on location.

rost in Wisconsin - Historic

Median Date of First Occurrence of Fall Frost

Current dates of the first frost in Wisconsin are shown on the following map:

Most current date of first frost in Wisconsin

Most current date of first frost in Wisconsin

Here is the current information for a larger portion of the Midwest:

Current date of first freeze for locations in the US Midwest

Current date of first freeze for locations in the US Midwest

Indian Summer

Indian summer is a period of unseasonably warm, dry weather that sometimes occurs in Autumn.  The US National Weather Service defines this as weather conditions that are sunny and clear with above normal temperatures, occurring late-September to mid-November. It is usually described as occurring after a killing frost. There may be several occurrences of Indian Summer in a fall season or none at all.

Late-19th century Boston lexicographer Albert Matthews made an exhaustive search of early American literature in an attempt to discover who coined the expression. The earliest reference he found dated from 1778, but from the context it was clearly already in widespread use. For a detailed discussion of possible origins for the term, see this article. Although the exact origins of the term are uncertain, it is thought to have been based on the warm and hazy conditions in autumn when native American Indians chose to hunt.

Indian Summer

A Beautiful Indian Summer Day

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