Better forecasts are on the radar for the Northland as Weather Service upgrades technology

• Radar dish

The National Weather Service Duluth office radar dish as seen inside the large radar dome. The radar is being upgraded to give forecasters more live data on severe thunderstorms, rain and winter storms. The dish pointed straight up to allow crews to install the upgraded equipment. (Clint Austin / caustin@duluthnews.com)
• Working on tower

Don Stevens, who works for a contractor for the National Weather Service, installs components Wednesday on the 30-meter tower for the upgrade to the National Weather Service radar system. (Clint Austin / caustin@duluthnews.com)
• Data example

An example of data from the new dual-polarization radar. By transmitting and receiving radio waves on horizontal and vertical axes, the radar will be able to more accurately identify the differences between rain, hail and snow and the amount of precipitation from a weather system. (Clint Austin / caustin@duluthnews.com)

Talk about it

The radar at the National Weather Service office in Duluth will be out of order for a few days but will come back online better than ever.

Crews are installing a new type of radar, called dual polarization, that will be better able to detect heavy rain that could cause flash floods, see through storms to identify the debris clouds caused by tornados and even tell the subtle difference between rain, sleet and snow.

It’s part of a $50 million upgrade to the U.S. radar system that will see all 160 National Weather Service and military radars upgraded to dual polarization. About 67 upgrades have been completed or are in the works, with the remaining 93 expected to be completed in 2013.

Green Bay and Marquette already have the new system, while the Twin Cities and Grand Forks will get theirs soon.

The result should be better short-term forecasts and better warnings when threatening weather develops.

Work started in Duluth on Wednesday and the new system should be operational by Monday, said Dan Miller, science and operations officer for the National Weather Service in Duluth. It may take a while before all the bugs are worked out and before forecasters can fully interpret the huge amount of new data provided by the new system, Miller added.

“Radar is our most critical data set to tell where storms are and what they are doing and where they are moving… and this is the most significant upgrade in radar since Duluth got Doppler radar in 1996,’’ Miller said. “This is going to give us a lot more detailed information on what’s going on in those storms.’’

For example, the old Doppler radar often mistook falling hail for extremely heavy rain, leading to gross overestimates of how much rain actually was falling. Dual polarization can separate the two. The new radar also will see true heavy rain better, leading to quicker forecasts for flash floods. The new system can even differentiate between the size and shape of water droplets in clouds, and whether the precipitation in the clouds is rain, sleet or snow.

Nearly all the radar used by forecasters — including most local TV stations, the Weather Channel, AccuWeather and the Weather Underground — comes from the 160-radar National Weather Service system.

Current weather radars transmit and receive pulses of radio waves that measure only the horizontal dimensions of clouds and rain droplets. The “dual-pol’’ radar transmits and receives the pulses in both horizontal and vertical dimensions.

If there is a tornado on or near the ground, Miller said, the dual-pol radar will detect debris, such as flying grass, leaves and rubble. Combined with a hook echo and the rotation already seen by the current Doppler system, dual-pol will help confirm tornados even when no one can see them on the ground. That helps eliminate false alarms and can help give additional warning time.

The dual-pol system is credited with giving people in Springfield, Mo., a full 20 minute warning before February’s devastating tornado hit, while folks in Branson got 35 minutes warning — double the national average under traditional Doppler radar.

“Especially if it’s happening at night, this gives us a good tool to confirm what we may have suspected was going on,’’ Miller said.

The dual-pol radar also outperformed traditional Doppler during Hurricane Irene that struck the Carolinas in August, predicting rainfall in the giant storm more accurately by a matter of several inches.

“This is very encouraging given that this is the first hurricane scanned by an operational dual-pol radar in the U.S.’’ Paul Schlatter, a special advisor on radar to the director of the National Weather Service, said in a statement after the hurricane. “The potential for dramatic rainfall estimating with dual-pol is great. But there is still much testing and refinement to be done.”

By theory, dual-polarization radar also should help forecasters watch for snowfall intensity better than the old system, Miller said. So far, however, there hasn’t been enough history with the new system in snowy areas to test the theory.

“There should be signals in the new data that will help with snowfall, but the jury is still out on how much it will help,’’ he said.

The dual-pol system is so sensitive that biologists say they can use it to study the movement of bats and birds at night. It can even pick up swarms of insects — and can identify all those flying critters from rainfall.

While the Duluth radar is out of order during the changeover, Duluth forecasters will rely on radar in Minneapolis; Grand Forks; Green Bay; Marquette, Mich.; and Thunder Bay and Dryden, Ontario, to help monitor weather systems moving across the region.

Tags: news, weather, duluth, technology, fccnetwork