Tech • System will better estimate precipitation amounts, locations.
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Salt Lake City's National Weather Service office is getting the first major upgrade to its radar network since Doppler was introduced in the early 1990s.
Dual polarization radar, which has been in use since June near Cedar City, is expected to be operational along the Wasatch Front by the end of the week.
"What it will allow us to do is to better determine precipitation types," said Randy Graham, science operations officer for the Salt Lake office.
He said the new radar will aid forecasters with short-term forecasts, often to within an hour.
"It will help us differentiate storms capable of producing very heavy rain from those producing more typical rainfall," said Graham. "It will help us pick out storms that have large hail."
Conventional Doppler radar sends out a horizontal pulse that gives forecasters a one-dimensional picture of whatever is in the air, be it precipitation or something else. The older style of radar can see the precipitation but can't distinguish between rain, snow or hail.
Dual-pol radar sends and receives both horizontal and vertical pulses. That provides a much more informative, two-dimensional picture of phenomena such as rain, hail, snow, ice pellets and other flying objects, thus improving the forecasts.
According to the National Weather Service, the new system will:
• Provide better estimates of total precipitation amounts.
• Give forecasters a better idea of the size of rain drops, snowflakes, hailstones and drizzles.
• Offer much improved ability to identify areas of extremely heavy rainfall that are closely linked with flash floods.
• Provide improved detection and mitigation of nonweather-related radar echoes, such as smoke plumes or dust.
• More easily identify the melting layer the elevation at which snow becomes rain to better forecast which areas will receive which type of precipitation.
What it won't do is help with longer term forecasts.
"What they are looking for mostly [with the new radar] is weather forecasting in the here and now," explained Randy Julander, snow survey supervisor for the Natural Resource Conservation Service in Salt Lake City. "It will allow them to be able to help forecast a more intense event on a finer time scale and with a finer spatial scale. They can look at it pretty much when it hits the ground."
That doesn't help scientists such as Julander who look at long-term precipitation trends.
But it could help weather forecasters who contract with the Utah Department of Transportation to create individual reports for each of the agency's four regions.
"If we don't already have [the new radar], we would include it in our reports," said spokesman Adan Carrillo of UDOT. "If they are willing to share, we're more than happy to incorporate that into our report. It's more efficient."
Graham stressed that the new radar system, under development for the past 30 years, does not replace Doppler radar but provides additional information. For example, if a storm appeared to hold large quantities of small hailstones capable of covering a major highway, forecasters would be able to warn motorists, he said.
Forecasters have been required to spend more than 20 hours training on the new system using simulators. The agency hopes to have the new system online throughout the country by next spring.