Snow pack, forecasts point to an ‘active fire season’
By Ann McCreary
After last summer’s severe wildfire season, no one wants to hear that the coming summer could be just as bad.
But that’s what a fire weather consultant predicts, based on current weather patterns and long-term forecasts.
“We’re going down a path right now and the path is leading to an active fire season” in eastern Washington and the Pacific Northwest, said Paul Werth, a meteorologist who has a private weather consulting business.
Werth has developed a statistical model that incorporates several predictors of fire season severity, including Pacific Ocean sea surface temperatures, upper level pressure patterns, seasonal precipitation, long-term drought, projected summer rainfall, and mountain snowpack information.
His model “pretty strongly points to an above-average active fire season” in the Pacific Northwest in 2015, said Werth, who operates Weather Research Consulting Services in Battle Ground, Washington.
In particular, lower-than-average winter snowpacks, predictions of above-normal temperatures and below-normal rainfall, and warmer Pacific Ocean surface temperatures could contribute to conditions that lead to an active fire season, Werth said.
Werth worked for 36 years as a fire weather meteorologist for the National Weather Service and also worked in that capacity for the National Interagency Fire Center. He shared his observations last week at a meeting in Brewster focusing on preparing for future wildfires.
A Washington Water Supply Outlook report issued this month by the Natural Resources Conservation Service (NRCS) found statewide snowpack levels are at only 51 percent of normal. At this point in winter, Washington should have received about half of the total snowfall for the season. However, most areas are measuring only about one-fourth of the snowfall average, the report said.
Methow doing better
Some areas near the Methow Valley, however, are faring better in terms of snowpack than other parts of the state, said Scott Pattee, a water supply specialist with NRCS who prepared the Water Supply Outlook.
“You guys are the lucky ones. For the Methow River basin you are sitting at about 114 percent of normal” in terms of snowpack, Pattee said.
SNOTEL (snow telemetry) monitors show snowpack readings to be 133 percent of normal at Harts Pass and 108 percent of normal at Rainy Pass. The snow water equivalent (the water content of the snow) in the Columbia/Methow River basin is 91 percent of average.
This area appears to be an outlier, however. In contrast to readings in the mountains above the Methow Valley, the lower Columbia River basin has about 41 percent of normal snowpack, Yakima basin has 52 percent and Spokane River basin has about 57 percent, according to the water supply report.
The big snowpack measurements at Harts Pass and Rainy Pass are the result of “some kind of microstorm that hit from Rainy Pass through Harts Pass and dumped in the Conconully basin and then died, or tracked into Canada. It didn’t really hit anywhere else,” said Pattee.
“The Methow basin, with the current snowpack and rainfall, is forecast at 113 percent [of average] flow April through September,” Pattee said.
The prognosis for future snowpack accumulation is not encouraging, Pattee said.
“The National Weather Service climate prediction is calling for above normal temperatures and below normal precipitation for the Pacific Northwest,” Pattee said last week.
“The high temperatures are certainly true. We have sites at 5,000 to 6,000 feet [elevation] with temperatures of 40 degrees, about 15-20 degrees above normal,” he said. “As far as building the snowpack, that doesn’t bode well.”
Opposite of last year
This year’s pattern appears to be the opposite of last winter, when there was little snow at the beginning of the season, but lots after mid-winter. “Last year kind of ended up normal” in terms of snowpack, Pattee said. “The faucet turned on in January and didn’t shut off until March.”
However, it’s unlikely that the deficit can be overcome this year, he said. With every day that passes, the potential for additional snowpack drops, he noted. “Typically we should be receiving snow almost every day this time of year. January is one of our biggest snow months.” But that’s not happening, Pattee said.
“A persistent ridge of high pressure has blocked Pacific Ocean storms from penetrating the region,” Werth said in a snowpack evaluation issued this month. “Even though we have three months left in the snowpack season…the current snowpack is so far below normal that it is historically impossible to make up the deficit by April 1,” he said.
Werth has analyzed the connection between snowpack and the rate at which the snowpack melts to develop a “spring snowpack index” that indicates the severity of the coming wildfire season. He has studied the correlation between snowpack, snow melt rates and wildfires, examining statistics back to 1954.
“The spring snowpack index is the best predictor I have for the fire season,” Werth said.
“The state snowpack could drop to 40 percent of normal by April, and that could put us in a severe fire season,” he said.
Topography matters
The Methow Valley and similar narrow, rugged drainages are “really susceptible to hot, dry windy conditions” conducive to wildfire because of their topography, Werth said.
When marine air pushes up over the Cascade Mountains it drops down into the narrow valley and flows toward the Columbia River. As the air descends down the valley it compresses, warms and dries through a process called “adiabatic warming.”
“The Methow Valley is a wind tunnel that the air is getting forced down 4,000-5,000 feet, and getting hotter and drier as it moves down the valley. For every 1,000 feet [elevation loss] air warms 5.5 degrees,” Werth said.
“That’s why it’s really a hot spot for fire, just due to topography,” he said. The Entiat Valley, Wenatchee Valley and Lake Chelan see similar weather patterns, he said.
While his analysis points to a very active fire season, Werth offered this caveat: “Nothing’s 100 percent in weather.”
Even when indicators predict a severe wildfire season, “there are years where we’ve had fairly mild fire seasons,” Werth said. “The prudent thing to do is be prepared and watch how spring and summer progress.”
