A) weatherTAP is a web site which provides direct access to several types of weather information. The site is somewhat unique in that it is updated as soon as the data becomes available. Other weather sites update information in a periodic fashion. For example, some other weather web sites updates their radar images every ten minutes (regardless of whether any new information is available) and text products every hour. We are unique in that almost as soon (within seconds) as the data becomes available to us, it is available on the web. That is why we are "the fastest weather on the web."
Q) What information does weatherTAP provide?
A) We provide several types of weather information. We provide real-time NEXRAD doppler radar for approximately 140 sites in the continental United States. National and Regional radar imagery is also available. These images are actually composites of the individual sites.
In addition to radar data, satellite imagery from the GOES-12 and GOES-10 satellites is also available. We provide both visible, infrared, and water vapor imagery for the North American continent as well as high resolution regional images.
We also have AFOS graphics available on the aviation weather portion of our site. These are maps and plots prepared by NWS meteorologists. In addition, we receive forecasts, current conditions, and aviation text products from the NWS. As with the images, these are updated on the web as soon as they are made available to us.
A) NEXRAD is short for "next generation radar." The official name is WSR-88D. This system was installed by the U.S. government to provide comprehensive weather information for the United States. See the Radar Tutorial for more information.
Q) How often is the radar updated ?
A) Currently the radar operates in one of three modes. In "clear air" mode, the radar dish makes a complete scan of the sky and produces an image about every 10 minutes. In "precipitation" mode, the radar produces a new image about every 6 minutes. If there is any precipitation at all in the field of view of the radar, then the station will usually change over to "precipitation" mode. A third mode exists but is rarely used. This is the "severe weather" mode and is usually only used for tracking hurricanes,etc. It produces a new image every 5 minutes.
After new data becomes available at the radar site, it is transmitted via satellite to Harris. They process the data and produce an image. The image is then transmitted to us via satellite. Within seconds, it is available on the web. This whole process usually takes less than a minute or two.
Q) What does radar imagery show me ?
A) Radar images can be used to detect precipitation and/or storms. Generally, the stronger the signal, the more intense the weather system. Sometimes radar may pick up other things such as intense smoke or volcanic ash, but this is relatively rare, and usually shows up as light precipitation. See the Radar Tutorial for more information.
Q) Why are there always radar echoes in the center of the radar image ?
A) These radar echoes are not clouds or precipitation, but are usually mountains, hills, buildings, and antennas. This is collectively known as "ground clutter". You see it at the center of the image because that is where the radar dish is located. To scan the sky, the radar dish must be tilted up slightly. As the distance from the dish increases, then obstacles must be very large before they will produce an echo. Obstacles close to the dish, however, do not have to be as big to produce echoes. That is why you usually see ground clutter in the center of the image.
Ground clutter is usually more noticeable when the radar is in "clear air" mode, because the radar is more sensitive. When switched to "precipitation" mode, the area of ground clutter usually shrinks.
We have attempted to filter out ground clutter from the national and regional radar images.
Q) What is the GOES satellite ?
A) GOES stands for the "Geostationary Operational Environmental Satellite". There are currently two of these satellites actively monitoring the United States, GOES-12 and GOES-10. Both of these satellites are in geostationary orbit about 22,500 miles above the equator. This type of orbit makes the satellite appear to be stationary from Earth. That is why home satellite dishes do not have to be moved to track TV satellites. GOES-12 is currently in orbit on the eastern side of the U.S. For national images, GOES-12 can just barely cover all of the U.S. Currently regional images are limited to areas east of Utah. We receive all of our satellite images from GOES-12. GOES-10 is currently over the western half of the U.S. This satellite completes the high resolution coverage of America.
Q) How often are GOES images updated ?
National images are generally updated about every 15 minutes.
Q) What does satellite imagery show me ?
A) weatherTAP provides two types of satellite image. The first type is a "visible" image. This simply means that the satellite is essentially taking a photograph of the Earth, just like you would with a normal camera. From above, you can see cloud cover and storm systems.
The second type of image is an "infrared" image. This image is produced by a camera that is sensitive to the "infrared" portion of the eletromagnetic spectrum, in a range our eyes cannot see. The warmer an object or air mass is, the more infrared energy it emits. The infrared image produced by weatherTAP uses a color code to depict variations of temperature in the atmosphere. Since clouds in the upper troposphere and lower stratosphere are very cold, these show up well on the image. This image can be used to track clouds, rain, and storms.
Q) It is 10:00PM and all I see on the visible satellite image is a black screen. The infrared image looks fine. What's going on?
A) Since the visible image is essentially a photograph, then you would not expect to see much from a photo taken at night. Since the infrared image does not rely upon sunlight to reflect light, then it is available at night as well as day. For a neat picture, look at an animated visible satellite image in the early morning. You should be able to see the sunrise from space !
Q) Where do the forecasts and current conditions on weatherTAP come from ?
A) Current conditions are observed and recorded by officials at reporting stations across the U.S. These stations are identified by a three-letter code. These codes appear on the local forecast maps, and those are what you click on to get conditions and forecasts.
Current conditions are recorded by officials at the stations, however, forecasts are usually prepared at regional offices by professional NWS meteorologists. The forecasts shown on weatherTAP are the "zone forecasts" for the zones that the stations reside in. A zone is usually a county or some other political boundary, although in some areas zones are delineated based on geographics features (i.e. California).
Q) How often are conditions and forecasts updated ?
A) The conditions are generally reported at the top of every hour. weatherTAP makes them available on the site as soon as they come in, usually less than five minutes after the hour. If radical changes occur in the current conditions for a station before the next scheduled report, then new conditions will sometimes be reported. weatherTAP always displays the latest reported conditions transmitted to us by the NWS. Forecasts are usually issued 2-4 times per day depending on the conditions. If a weather event occurs which leads to a radical change in a forecast, then a new one will be issued. As always, weatherTAP always displays the latest issued forecast.
Q) What are the funny lines for on the "Winds Aloft" and surface observation charts?
A) These are "Wind Barbs" and are used to indicate wind speed and direction. See the Wind Barb & Sky Coverage discussion page for more info.
Q) I can only view old data or old images on WeatherTAP, is something wrong?
A) Your browser is most likely saving older data in cache without asking for an updated page. You will need to change the settings on your browser to have it always request the most recent page. Here is how to do this for Explorer and Netscape:
NETSCAPE version 4.06 or higher :
Select EDIT | PREFERENCES from the file menu bar at the top of the browser,
then click the + in front of "Advanced", then select "Cache"
looking at the bottom you will find "Document in Cache is compared to
document on network" you want to select "Every Time" then click
on "OK".
INTERNET EXPLORER version 5.0 or higher :
Select TOOLS | INTERNET OPTIONS from the file menu bar at the top of the browser,
then half way down under the "General" tab you'll see "Temporary
Internet Files" click on the "Settings" button, now under "Check
for newer version of stored pages" you want to select "Every visit
to the page" then click on "OK" and "OK" to close
the Internet Options window.
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