Answers: Weather Radar

By Jack Williams ©2015

Q: I have been reading your column in AOPA Flight Training magazine for several years and I wanted to let you know you have inspired me to become very interested in the weather and especially how it effects my flying. My question is about where I can find the raw SD radar weather reports.  I see them briefly mentioned in various publications and there are even a couple of questions in the FAA Advanced Ground Instructors exam.  I would be interested in having these reports in my “Weather Tool Box”.

Scott, Huntersville, N.C.

A: First, you really don’t want to go to all of the effort needed to add SD radar reports to your pilot’s weather tool box. Ralph Butcher summed it up in his July 2008 Insights column in Flight Training: “Caution! Ignore the textual Radar Weather Report (SD/ROB). It is derived from the WSR-88D NEXRAD radar without human intervention. That information can be up to 80 minutes old and should only be used if no other radar information is available.”

The NWS Aviation Weather Center (AWC) doesn’t have any links to the coded SD/ROB reports, but does link to the Radar Summary chart, which is complied from these  reports. When I recently looked this chart had been done from reports that were 30 minutes old. The Radar Summary Chart, unlike other radar images, does show the heights of the tops of thunderstorms and also the direction and speed of movement of storms.

Mobile, Ala., NWS radar image from the NWS Aviation Weather Center Web site.

Mobile, Ala., NWS radar image from the NWS Aviation Weather Center Web site.

After looking at the Summary chart, I clicked on the AWC’s radar page, which has a U.S. map  (including Alaska and Hawaii) showing radar images that were only five minutes old from NWS radars. (I’ve never seen an image here that’s more than 15 minuets old.) If you click on a location on this map you get a close up image like the one on the right, which shows what the Mobile, Ala., NWS radar was seeing at the time.

The plain language translations of SD reports are listed as being available on DUAT, the FAA’s computerized weather data service for pilots. See my January 2009 Flight Training article on DUAT.

The FAA-NWS book Aviation Weather Services has detailed instructions for translating coded SD reports.  It’s available as free PDF download an FAA Web site page. SD reports describe in words what a local NWS radar saw in various directions and at various distances from the radar.  Say you were planning to fly due north and read that the radar had received echos from a thunderstorm in that direction 15 miles north of the radar, this could be useful information.  But, you’d have to know where the radar is located. And, to get an idea of whether the thunderstorm is isolated or part of a line you’d have to plot other locations. It’s hard to imagine doing this without a map.

But, why go to all of that effort?  The NWS is supplying continually updated images like the one above, which supply a pilot with a great deal of information, at a glance.

In addition to the AWC radar images, NWS local offices also publish continuously updated images from their local radars on the Web. With these you can toggle between the latest still image and a loop, which shows you movement of the echos the radar is detecting. To find the local office you want, go to the NWS organization page, which has links to local offices.

Finally, the question from the advanced ground instructor exam that you sent to me confirms that the FAA is still asking weather questions that have little to do with real world of pilots who are trying to obtain and use weather information.

Tom Horne summed it up in his January 2000 AOPA Pilot Wx Watch column: Many of the few weather questions on FAA exams “are designed to test just how well you’ve memorized those METAR and TAF codes, or find out where you’d look for certain types of reports or forecasts. In other words, quantitative questions. Nothing that could really reveal your weather-related decision-making skills.”

In this column Horne mentions a paper I presented to the American Meteorological Society’s Aviation Weather Conference in Paris, France, in 1991 on how the weather questions on all FAA exams could be improved. I also made the point that the FAA tests mislead many pilots about what they really need to know about the weather.

I last wrote about this topic in the July 2004 issue of Flight Training. The National Research Council made similar points in its 1995 report, Aviation Weather Services. The report is available for free on-line reading on the National Academies Press Web site. The comments on pilot weather training are in Chapter 3, beginning near the bottom of page 35.

The question you sent nicely illustrates what Horne, myself, and the National Research Council said about FAA weather questions:

Q: Interpret the following radar weather report: LIT 1133 AREA 4TRW 22/100 88/170 196/180 220/115 C2425 MT 310 AT 162/110

The correct answer is: The maximum top of the cells is located 160 degrees and 110 NM from the station (LIT).

As we saw above, you’d find to answer to this question and many other practical questions about the weather you are thinking about flying into by going to minutes-old radar image.

You could spend a lot of time  studying pages 3-45 through 3-51 of Aviation Weather Services to learn how to read this code. Or you could be learning more about how to read radar images and what these images really mean. Doing this, of course, won’t help you pass an FAA written test, but it could help you avoid nasty weather in the real world.

By the way, the source of questions such as the one above is Aviation Weather Services: Advisory Circular AC00-45F (FAA Handbooks). In addition to helping you answer questions on exams, you can use it to learn more about using NWS products.

My latest book, The AMS Weather Book: The Ultimate Guide to America’s Weather, will help you better understand the weather and the devices used to observe it, including weather radar.  My books page has more about it.

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