Map Information : Weather Underground

Map Information

A color-filled contour map showing current temperature. The key below the image shows the corresponding temperature value for each color. This map can be double sized and animated.

Radar Map

A radar map showing the current precipitation data for the United States. 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. This map can be double sized and animated.

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. This map can be double sized and animated.

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. This map can be double sized and animated.

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. This map can be double sized and animated.

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. This map can be double sized and animated.

UV Forecast

A color-filled contour map showing the forecasted Ultra Violet index (UV index) at noon local time. The UV index indicates the strength of the sun's ultraviolet rays that cause sunburn. The higher the number, the stronger the UV rays coming in contact with your body. The key below the image shows the corresponding UV index and minutes to skin damage at noon for each color. For more information on UV index, see The Climate Prediction Center. This map can be double sized and animated.

Satellite Map

The current infrared satellite image for the United States. 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. This map can be double sized and animated.

Fronts

This map shows the current radar, fronts positions, and areas of high and low pressure for the United States. Blue fronts are cold fronts, red fronts are warm fronts, alternating red and blue fronts are stationary fronts, and purple fronts are occluded fronts. Front positions are updated every 3 hours. This map can be double sized and animated.

Snow

A color-filled contour map of the current snow depths across the United States. 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.

Flight Rules

A map depicting the the flight conditions at each airport that reported in the past 2 hours across the United States.
Visual Flight Rules (VFR) - the pilot has the responsibility for seeing and avoiding other aircrft, towers, mountains, etc.
Marginal Visual Flight Rules (MVFR) - conditions between VFR and IFR. Generally defined as visibility between 3 and 5 miles, and ceilings between 1,000 and 3,000 feet.
Instrument Flight Rules (IFR) - the pilot may be in clouds, flying solely by instruments, and therefore unable to see other aircraft. The controller takes the responsibility for aircraft separation.
Low Instrument Flight Rules (LIFR) - ceiling below 500 feet AGL and/or visibility less than one mile.
This map can be double sized and animated.

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). The jet stream images are updated twice per day, at approximately noon and midnight EST. This map can be double sized and animated.

Ozone Pollution

The data plotted is sent to us approximately one hour after it is collected, between 8am and 8pm, from the The Environmental Protection Agency (EPA). Data is currently missing for eight states, but data for some of these states will be added over the next year. The EPA uses its Air Quality Index to provide general information to the public about air quality and associated health effects. An Air Quality Index (AQI) of 100 for any pollutant corresponds to the level needed to violate the federal health standard for that pollutant. For ozone, an AQI of 100 corresponds to 0.08 parts per million (ppm) over an 8-hour period -- the current federal standard. Over half of the U.S. population lives in areas where the AQI exceeds 100 and violates the federal health standard at least once per year. For more information, visit our Air Pollution page, or our Ozone Pollution page.

NDFD Graphical Forecasts

Data for these maps are gathered from the National Digital Forecast Database (NDFD). Currently we offer Prevalent Weather, Temperature, Maximum Temperature, Minimum Temperature, Dew Point, Relative Humidity, Sky Cover, Precipitation Amount, 12 hour Probability of Precipitation, Snowfall, and Convective Hazard Outlook maps for the the lower 48 US states. All of these are considered to have "Operational" status. We will provide additional NDFD-derived imagery as more products / regions become operational. For more information regarding the NDFD, please visit the NDFD Home Page.