New Radar Equipment Heralds More Precise Weather Forecasts in County

Dual polarization will give more information about what’s in the clouds. Forecasting is a challenging “guessing game,” meteorologists say.

In a Rancho Bernardo office, a group of people spend their days and nights looking at huge screens of multi-colored high and low pressure systems moving across Southern California. It's a "guessing game," trying to assess what the images mean for local residents.

These are the staff of the National Weather Service (NWS), who work around the clock, seven days a week, supplying updates about where the rain may fall and how much snow we may see in the mountains. It can be more of an art than a science, they say, but new technology that will go into use this summer will provide more information—and that could improve forecasts.

The equipment is called dual polarization radar, and it has been added to a NWS Doppler radar based at Marine Corps Air Station Miramar. It will transmit and receive waves that slice through clouds in both horizontal and vertical planes, and then compare the two readings. This will give meteorologists better data about possible incoming rain, hail or snow.

Staff say anyone traveling on Poway Grade can look to the south and see the "lolly pop" shaped white dome which houses the doppler radar. The "dual pol" on it will go into use in July. The NWS operates 159 doppler radar around the country, meterologist Alex Tardy told Patch this week. Many are still owned by the military.

Forecasting is highly technical work, requiring not just the radar but computer modeling, hydrogen-filled rubber sounding balloons and a county full of weather stations. The stations are owned and operated by a variety of sources: the NWS and Federal Aviation Administration, U.S. Forest Service and San Diego Gas & Electric, Co., and some are in the back yards of residents who have applied to the NWS to provide information.

Of course, the data from private sources is not always spot on.

"The official climate sites are at airports," Tardy said, "and they're maintained by the government. A lot of the private stations are operated by radio enthusiasts. Most providers are pretty good but some we can't vouch for."

On occasion, NWS meteorologists go out in the field to look at some of the privately owned units. Over the years, they've encountered rain measuring devices that are too close to spoutings or a temperature unit that's too close to a sun-warmed roof to be accurate.

Microclimates exist throughout San Diego County, so sometimes the public might question the "official" readings. The NWS staff say that's because the airport units may read differently from a resident's own measurements a mile or more away in the same town.

The network of all these government and private weather stations is called the Mesonet. Click here to view the Mesonet map, which shows the locations of the stations, their ownership and measurements, in real time. Click on the specific station to see even more weather data.

Knowing what's happening in real time is one thing, but interpreting what may happen tomorrow or a week from now is another. That's where the computer models come in. The NWS uses models from all over the world.

"Weather is worldwide, so we all share info," Tardy said.

"We have to decide which models might be the most accurate at any given time," meteorologist James Thomas said. "We look at model biases. Some may not perform as well when conditions are too cold. We look at which ones have been the most accurate in the past month."

Their models include the Weather Research & Forecasting Model, which is small scale and uses local topography. They also use the European Centre for Medium-Range Weather Forecasts (ECMWF), plus two from the National Oceanographic and Atmospheric Adminstration (NOAA) called NAM 12 (North American Meso) and the Global Forecast System.

They look at several different models to get an overview of the most likely expectations.

"Ideally, they all come together—the gradient lines," Thomas said. "But after a few days, it could look like a spaghetti plot, where all the lines of the various models shift apart."

"We use our guts, our experience and our brains to interpret the models and we make manual adjustments to them," Miguel Miller, another NWS meteorologist said. "It's a guessing game. It's really fun, really challenging."

The NWS office overlooks a panoramic view of inland North County and the "real" weather happening at any moment, but, inside, the views are more "what if."

Staring for hours and hours, day after day, at layers of computer models and trying to guess what's coming can cause meteorologists to get into a bit of a  virtual reality mode, they say, but the NWS personnel have learned to translate the moving masses of color on their screens into the real world for the public they serve.

"In the 1980s, we improved the way we communicate to people," said the former director of the NWS in San Diego, Jim Purpura, who is now a consulting meteorologist for a private company. He was visiting the NWS office on Tuesday, helping staff explain to journalists the finer points of dual polarization radar.

"It's not good enough to just issue a high wind warning and not explain what that is," he said. "People wonder, 'What does a high wind warning mean?'

Thomas made it clear on Tuesday that the high wind warning for East County that night was going to create "dangerous" driving conditons. He was correct. Winds of at least 62 mph were clocked in the desert, pushing over one mobile home in Ocotillo Wells and whipping debris through the air, as reported in . Part of Interstate 8 was closed off to high profile vehicles and damage to buildings was reported in Borrego Springs.

But sometimes meteorologists haven't hit the forecast so close to the mark.

Miller explained that there are times when all the models and all the meteorologists interpreting them might underestimate a storm.

"It's the weather," he said. "Sometimes it throws something at us that we miss."

Jim Purpura - Redhawk Weather March 08, 2012 at 04:36 PM
Nice story, Julie! Enjoyed the media workshop! As you mentioned, the interaction of the science and social science help fuel improvements in the NWS effectively communicating the warning message to the public over the last 10 or so years... Jim Purpura weathercurrents.com


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