Radar blind spot exposes Southwest Colorado to dangerous storms — The Durango Herald

Graphic credit Cliff Vancura via The Durango Herald and Rocky Mountain PBS.
Graphic credit Cliff Vancura via The Durango Herald and Rocky Mountain PBS.

From the Cortez Journal via The Durango Herald (Jim Mimiaga):

“We can’t forecast what we can’t see, whether it’s water supply or extreme weather,” said Joe Busto, a researcher with the Colorado Water Conservation District.

Weather conditions and forecasts for the region rely on radar installations in Grand Junction, Flagstaff and Albuquerque. None of the stations detect low-altitude, dangerous conditions in an area that reaches from Alamosa west to the Grand Canyon, and from Gallup north to Moab, said Jim Pringle, a meteorologist with the National Weather Service in Grand Junction.

“We would like to see a radar station in that area,” he said. “On the weather maps, you can see the gap in your area where radar does not hit.”

Over the past few years, several severe and damaging storms hit the Four Corners without warning. They include:

On Feb. 22 and 23, 2015, a winter storm hit San Juan County, Utah, with forecasts for 11-16 inches of snow. The storm dumped up to 3 feet of snow in the northeast Navajo Nation, leaving waist-high drifts in some areas. The Navajo tribe declared a state of emergency. Local roads became impassable and an estimated 350 families were snowed in. Multiple power outages were reported, and cellphone towers were inoperable. Schools in Bluff and Montezuma Creek were closed until March 2 and 3, respectively, and schools in Monument Valley were closed through early March.

In summer 2015 on Southern Ute land, a funnel cloud was reportedly witnessed by government officials, but faraway radar stations couldn’t detect it. Residents had no warning.
On Sept. 23, 2015, a severe hailstorm at Vallecito Reservoir caught residents by surprise. The storm produced hailstones up to 1.25 inches in diameter and killed a mallard duck.

On Dec. 23-24, 2015, more than a foot of snow fell during a blizzard that caused white-out conditions and closed U.S. Highway 491 from Cortez to Monticello for 17 hours. The storm caused a 19-car pileup and stranded motorists. The potential for significant snowfall was missed because weather radar couldn’t see the changing, low-altitude storm.

In radar blind spots, on-the-ground weather watchers such as meteorologist Jim Andrus of Cortez provide the eyes for the Weather Service’s real-time weather data.

“I’ve had several incidents where there were no radar echoes showing up on the weather channel, but it’s raining or snowing outside,” Andrus said.

The lanky, silver-haired apartment manager with a weather-science mission is constantly looking up, monitoring the skies where technology fails. For 19 years, he’s filed regular reports to the NWS using the internet at the Cortez Public Library.

His on-the-ground reports often fill gaps in forecasts. In summer 2014, Andrus alerted the service to a severe storm that approached Cortez from a blind spot near Ute Mountain. The storm had the potential for hail and high winds, and NWS issued a warning based on Andrus’ report from the ground…

Radar just one set of eyes

The National Weather Service relies on three levels of reporting to provide forecasts for Four Corners residents. If one falls short, the forecast does too.

Satellite images show cloud activity from above and are valuable because they show the reach and route of storms. Ground-based radar, such as a Doppler system, looks into a cloud to determine the potential for precipitation and the severity of storms.

Blind spots are caused in part by the curvature of the Earth. When straight-line radar beams reach Southwest Colorado from the closest station in Grand Junction, they’re too high to do much good.

“In Durango for example, the radar’s lowest angle is 23,500 feet, but the top of winter storm clouds is at 18,000 feet,” Pringle said. “We’re not seeing the whole picture.”

In Cortez, the radar’s lowest reach is at an altitude of 23,000 feet. At Bluff, Utah, it’s 27,000 feet, and at the Navajo Nation south of Bluff, it’s 29,000 feet. In Pagosa Springs, it’s even worse, an altitude of 39,000 feet.

Radar benefits water supply

Since 2009, the Colorado Water Conservation District has partnered with the National Oceanic and Atmospheric Administration to research the need for radar in Southwest Colorado for more accurate water supply forecasts in rivers and reservoirs.

The study placed a temporary Doppler radar at the San Luis Regional Airport in Alamosa during the 2014-15 winter and compared its water supply data with radar maps from the weather service’s faraway installations. “The forecast was four times more accurate,” said Busto, a water district researcher and an author of the study.

“We’re building a business case that the radar black hole is killing the water world because we’re not keeping track of how much water we have,” he said.

The temporary radar will return to the Alamosa airport next winter to continue the study.

“The benefits of better observations and forecasts are tremendous,” said Craig Cotten, a Division 3 engineer with the Colorado Division of Water Resources. “Our compact operations are based on stream flow forecasts. Inaccurate forecasts can cause unnecessary curtailment of ditches, over or under delivery of compact obligations and disruption of priority system.”

During a runoff period from the winter of 2013-14, for example, Grand Junction radar estimated 3,000 acre-feet of water for the southern San Juan Mountains, but the temporary radar in Alamosa showed 34,000 acre-feet of water supply.

Buston said local radar more accurately reads precipitation levels in low-altitude winter storms that tend to hug the mountains.

“In our part of the world, snowpack is our water bank, and people pay to lease shares, but when we are missing how much water there is, it’s like your banker not knowing how much is in your account,” Busto said.

For example, the study showed the 2013 water year forecast was 230,000 acre-feet, and the actual water supply was 344,000 acre-feet. The 2005 forecast was for 795,000 acre feet, but the actual water supply was 683,000 acre-feet.

Water forecasters say that by adding radar data to satellite images, Snotels and stream data in place now would improve local river runoff and reservoir forecasts.

What’s the cost?

In the water conservation board study, ideal locations for a permanent radar station were determined to be at regional airports in Alamosa, Durango and Montrose. Busto said the Cortez Municipal Airport is also a potential location for a Doppler radar station.

Depending on range capability, radar units cost between $2 million and $10 million, and are typically funded by state and federal governments. Portable units run about $500,000.

After the West Fork fires in 2013, a portable Doppler radar system was installed on Wolf Creek Pass to monitor flash flood conditions in the fire-damaged area.

Busto said it was effective in detecting storms capable of generating flash flood conditions, and warnings were issued. The same storms did not show up on radar systems in Grand Junction.

“Our mission is to protect lives and property, and the more resources we have to monitor weather, such as radar, then we can do that better,” Pringle said.

Busto pointed out that relying on satellite data to determine flash flood potential caused a “cry wolf” scenario for emergency managers. Every time satellite showed clouds in the area, erroneous warnings were sent out to residents, but nothing would happen.

Improved radar coverage would also improve airport operations, said Russ Machen, manager for Cortez Municipal Airport.

During winter storms, Machen relies on weather forecasts to plow the runways, and when the forecast is off, it can delay runway maintenance.

“The pilots would also appreciate more accurate regional radar to determine flight conditions,” he said.

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