the WEATHER CORNER

Doppler radar now on Web in real time

BY JAN NULL
Special to the Mercury News 

A decade after the National Weather Service began deploying new Doppler radar systems, it is finally able to put its own radar imagery directly onto the Internet in real time. 

Until Jan. 1, the weather service had been contractually prohibited from doing that, with all distribution provided by private vendors, usually with a time delay. Or some kind of fee was charged.

The weather service signed those contracts because the Internet was still an infant when the new radar came online in the late 1980s and early 1990s, and there was no infrastructure to distribute the information directly to the public.

Several large private vendors were given rights to the data for an annual fee, and they distributed it, primarily to the media.

The new National Weather Service radar Web sites are well-conceived and very functional with promises of adding more data and features.

To access local radar data from the WSR-88D -- Weather Surveillance Radar-1988 Doppler -- from atop Mount Umunhum in the Santa Cruz Mountains, go to http://www.wrh.noaa.gov/radar/latest/DS.p19r0/si.kmux.shtml.You can see the rainfall reflectivity from the base -- or lowest -- level, or a composite of radar returns from scans of multiple levels. There also are radar estimates of rainfall amounts during the past hour and a storm total. 

However, in the West, where many radar sites are atop mountains -- Mount Umunhum is at 3,400 feet elevation -- the radar beam scans above much of the rain at lower altitudes, undercounting precipitation.

These images are created only from the reflectivity function of the radar and do not take advantage of the Doppler capabilities to see horizontal movement of rainfall. 

Each Web site has navigational arrows to access adjacent weather radar sites, or you can reach other radars from a national map on the Web at http://weather.noaa.gov/radar/national.html. There also is a nice online radar tutorial at http://www.wrh.noaa.gov/radar/radinfo/radinfo.html 

Q. Growing up in Redwood City, I was repeatedly told that the city had the best climate in the United States and the civic slogan to prove it (and thus, by inference, I was lucky to be living in such a place). The slogan ``Climate Best By Government Test'' popped into my mind when I read about your Camelot Climate Index. Were you aware of Redwood City's fabulous, self-aggrandizing status of climate champion? Surely San Diego is but a mere pretender to a title that was scientifically decided decades ago. Here is some Internet propaganda to back up my claim: http://www.redwoodcity.org/about/local_history/exhibits/climate_best/climate_best.html  .  I realize Redwood City might not have been in your original database and thus could not have figured in the calculation. However, historical precedent has been set.  Kevin Vranes - Columbia University, New York

A. I am very aware of Redwood City's slogan, having worked for the National Weather Service there from 1974 to 1994, when the agency ill-advisedly moved to the foggy confines of Monterey. Although Redwood City in 1925 touted the government test, which actually was part of climate surveys that began before World War I, the same Mediterranean
climate applies to most of the Bay Area. It always pays to have a good PR person, I guess. Redwood City was not in my database, but I'm sure it would rank with San Jose at about second place.

Q.  Some locations are sometimes missing in hourly weather reports, or sometimes the temperature is reported but other observations are missing. This occurs even at airports that broadcast complete hourly reports on aviation frequencies. Why?  
Ed Taft - Mountain View

A.  Getting the current weather observations from an airport station to your radio or television is a multipart process. If any single link fails, the data doesn't get posted.

Most airport observation stations are automated and dial into a Federal Aviation Administration computer system at 55 minutes after each hour. The data then goes through a gateway to the National Weather Service computer system for distribution to weather service offices and to other users. 

The data is in a coded or shorthand format called METAR. Local weather service offices decode it into English and package it with other local weather observations into a single product called an hourly summary.

This is done on the hour with whatever data is available, and again 10 minutes after the hour when all the data should be in.

These summaries are transmitted back into the weather service computer system for distribution to other offices and outside users such as the Associated Press and your local radio station. They also are distributed on the Internet.

If any one of these computers, gateways or networks is down, some of the data may be missing from the final product. 

To see an example of a coded METAR report and the final summary for San Jose, go to http://www.phx.noaa.gov/data/sfomtrsjc.html  or www.phx.noaa.gov/data/sfoswrca.html.

Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o Weather Corner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. You also telephone and fax questions at (510) 657-2246 or e-mail them to (weathercorner@ ggweather.com).