Radar

Map Descriptions

Fronts – This map shows the current radar, frontal boundaries, and areas of high and low pressure for the United States. Cold fronts are depicted in blue, warm fronts in red, and stationary fronts in alternating blue and red. Occluded fronts are depicted in purple. Front positions are updated every 3 hours. Areas of constant pressure are bound by white contour lines and show changes from high to low pressure. The key below the image corresponds to the radar.

Jet Stream – A color-filled contour map of the wind speed where the atmospheric pressure is 300 hPa. Arrows showing the direction the wind is blowing at that level are overlaid. A pressure of 300 hPa corresponds to an altitude of approximately 8000 – 10000 meters above ground–the altitude where the jet stream is typically found. The data shown is the 6-hour forecast from the AVN computer model, which is run twice daily at 00 and 12 GMT by the National Center for Environmental Prediction (NCEP).

Vis Sat – Visible satellite images can be thought of as photographs of the earth from space. Since they are like a photograph, they are dependent on visible light (brought by the sun). As a result, visible satellite pictures only work during daylight hours. This is the greatest drawback to using visible imagery. Also, since a visible satellite picture is basically a photograph, thicker clouds (which reflect the most sunlight) show up very bright, while thinner clouds (like cirrus) are hard to distinguish.

IR Sat – The current infrared satellite image. Infrared satellite images indicate the temperature of cloud tops. The cooler the clouds, the brighter the color on the map. Since air temperature generally decreases with increasing altitude, the cooler (brighter) the clouds, the higher the clouds. Unlike the visible satellite image, infrared satellites work at night.

Wind – A color-filled contour map showing current wind speed. Wind vector arrows are also displayed to show the wind direction. The key below the image shows the corresponding wind speed for each color.

Temperatures – A color-filled contour map showing current temperature. The key below the image shows the corresponding temperature value for each color.

Humidity – A color-filled contour map showing the current relative humidity. Relative humidity is the ratio of water vapor contained in the air to the maximum amount of water vapor that can be contained in the air at the current temperature. The key below the image shows the corresponding relative humidity for each color.

Dew Point – A color-filled contour map showing the current dew point. Dew point is the temperature to which the air needs to be cooled in order for the relative humidity to reach 100 % (when a cloud would form). The key below the image shows the corresponding dew points for each color.

Heat Index – A color-filled contour map showing current heat index. Heat index is the apparent temperature considering both the temperature and relative humidity. The key below the image shows the corresponding heat index for each color. This map can be double sized and animated.

Wind Chill – A color-filled contour map showing the current wind chill. Wind chill is the apparent temperature considering both the temperature and the wind speed. The key below the image shows the corresponding wind chill for each color.

Snow Depth – A color-filled contour map of the current snow depths. The key below the map shows the corresponding snow depths for each color. The data is taken from a U.S. Air Force data set that is updated once per day at about 8pm EST. The data appears to have underestimation errors in Michigan’s Upper Penninsula. This map can be double sized and animated.

Visibility – A color-filled contour map showing current visibility. Visibility is the maximum horizontal distance that can be seen. The key below the image shows the corresponding visibility for each color. Note that most observing stations in the U.S. use are automated, and use a visibility sensor that has a maximum range of 20 miles. Thus, the maximum visibility reported in many areas is 20 miles, even though it is actually much greater.

Air Quality – This colored contour map shows the current air quality index (AQI) with respect to ozone pollution, according to the Environmental Protection Agency (EPA). The key below the index corresponds to the AQI for each color.

UV –┬áThis colored contour map shows the forecasted ultraviolet index (UV index) for noon at local time. The sun’s ultraviolet rays can cause sunburn and other harmful damage to the body, and the UV index is proportional to the strength of the sun’s ultraviolet rays. The key below the image shows the corresponding UV index and minutes to skin damage at noon for each color.

Flu –┬áThis colored choropleth map shows the flu activity for the past week. The key below the image shows the corresponding flu outbreak frequencies for each color.