Aviation Weather: Radars There are few places in the United States which are not covered by National Weather Service Doppler radars. The images, yes there are several, can now be accessed through several providers, both at a cost and free. The main difference between the two is timing and advertising. The fee-based systems upgrade their views every five minutes on average, while most free systems only update every 15-60 minutes. The time difference is not enough to justify the fee-based systems for flight simulation use. As for the advertising, well free systems have to pay the bills some way. However, most of the time, the impact on the user is not a significant problem. One of the most well-known providers is the WSI Corporation fed Intellicast system. With update times of around 15 minutes, they are the aviation simulation pilots best bet. Below are links to several of the radar products offered by Intellicast. First. let's take a look at the national radar. Below is a sample image showing how differing colors are used to denote the intensity of showers. The bar at the bottom shows the range of colors and what they represent. Click on the image to open the current U.S. Radar Image from Intellicast. 
The first of the specialized images we will focus on are composites of major cities, derived from nearby Doppler sites. Next to the national composite, these are the most common images used by pilots for those routine flights. Use the drop-list to find the city you want, then hit the Go button. Just hit the back key on your browser to return to this site. Major U.S. City Radar Images While a static image such as those above show you where it is raining now, it does not give you any indication of where the radar returns _ be they rain, snow of thunderstorms _ are headed. If there are no returns nearby, the odds are precipitation or storms will not be a threat in the immediate future. If there are returns, you have a couple of options to see where the weather is headed. First, you could sit and watch the image for 20 minutes or so to try and determine movement. Time you could have spent flying. Second, you could download a radar loop. Again this takes time and only shows movement up to an hour or so in the past. Finally, you can take a two minute glance at the National Weather Service Radar Summary. The summary looks like any other Doppler image, with the exception of storm cell tops, direction, speed, and such. The example below shows how the maps may look. In the center of the image, we see a thunderstorm topping out at FL350 and moving just north of east at 11 knots. The image also indicates a chance of hail in the cell. Click on the image below to open the current U.S. Radar Summary Image from Intellicast. To check out the images for major cities, use the "Help for Radar Summary" drop down list. To return here, just close the Intellicast window Jump to Intellicast Radar Summary
Now these composite images provide a nice smoothed display. But in the end, they are still composites, which means a computer took the actual Doppler images and merged them. That process can result in some loss of data. That is why most serious weather watchers opt to take a look at the Doppler images themselves. Once again, the folks at Intellicast come through for us. The image below shows how the U.S. is dotted by Doppler sites. Click anywhere on the image to jump to the Intellicast United States Base Reflectivity site. Base Reflectivity is the most common Doppler product shown during television weather casts. Jump to Intellicast Doppler Images
And there are several more Doppler products which are available. Most require training beyond this piece, though some are within the scope of what we have talked about. For example, you can get a time loop of the base reflectivity. You can also take a look at the radial velocity. This is one of those more complicated images. It shows the direction water droplets are moving and how fast. Should you have an area with droplets moving very fast in opposite directions, there is a chance a mesocyclone, or a tornado nursery, could be forming. Even more detailed radar maps can be found on the Internet, at both free and fee-based sites. (For Flight Simulation Use Only) |
