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TJ Jerke, Forum Communications, Published August 10 2012

High pressure, dry months created drought

GRAND FORKS – A high-pressure system causing a shortage of rain and excessive heat is to blame for the drought conditions that have plagued the central plains states, according to drought experts.

Brad Bramer, science and operations officer with the National Weather Service, said the high-pressure system has been sitting over most of the central parts of the country all summer and isn’t likely to move out for several more weeks.

“The system causes air to sink, which prevents clouds and rainfall from forming,” he said. “So as the air sinks in, the atmosphere also warms up.”

The Red River Valley is sitting on the north end of the system that stretches south to Kansas and Oklahoma, he said.

The system contributed to the hottest 12 months in the country and hottest July on record for North Dakota, according to the Weather Service.

Bramer said it will take a big shift in the jet stream pattern over the northern hemisphere to push the entire system out of the area.

A shift that may come as the region moves into cooler temps in the fall, according to Brian Fuchs, a climatologist with the National Drought Mitigation Center at the University of Nebraska-Lincoln.

“When you have a strong dome of high pressure established over a region, it’s very hard to break that down,” he said. “We see systems out of Canada that will touch off some storms, but the dome of the high-pressure system deflects all that and storms ride over the top of it.”

The mitigation center produces a weekly map, known as the U.S. Drought Monitor, which tracks drought conditions using about 375 officials in multiple agencies from around the country, Fuchs said.

The map rates various areas of the country based on the scope and the severity of the drought conditions they are in.

Short and long term

According to the mitigation center, current conditions are not indicative of a long-term drought in this area.

A compilation of records dating back 110 years indicate that today’s dry conditions will let up in the future.

“It shows most of the dryness is shorter-term and on a longer-term scale, things are looking fine,” Fuchs said.

But preliminary data through Oct. 31, 2012, says Grand Forks could continue to see dry weather, with western and central portions of the state likely to continue as well.

The drought goes back to November, when little precipitation fell and warm temperatures didn’t go anywhere, Bramer said.

A mild, dry winter then made matters worse followed by warm spring and summer temps that increased the evaporation of the little moisture that was in the ground, which led to dryer conditions.

“That cascaded into the summer months as well as late-May onward when the warming trend was in full force,” Bramer said.

Another drought

Bramer compared this year’s drought to 1988.

He said a similar high-pressure system sat over the central Plains states, but was shifted farther north, leaving North Dakota right in the core of it.

“It was the last major one that affected a fairly large portion of the country, similar to our current one,” he said. “It shifted north so we were impacted more severely than this year.”

In 1988, the region was dryer but not as warm overall, he said.

This year, the high-pressure system led to the warmest summer on record, with little rainfall.

The Weather Service found June’s average maximum temp hit 79.6 degrees, 3.5 degrees warmer than normal.

July saw 10 days above 90 degrees, and had a monthly average temp of 74.8 degrees, six degrees warmer than normal.

Fuchs said the temps played a huge component this year, increasing water demands as plants and humans alike scrounged and consumed more water.

“The dry episodes really compound the problems,” he said.

But while dry, the central Plains states still received some rainfall.

In Grand Forks, June had 2.38 inches, 1.1 inches below normal. July, however, saw an above-average rainfall of 3.35 inches, 0.20 above normal.

“Two–tenths is still not going to put a dent into relieving a drought,” Bramer said.

Conditions

Cass and Traill counties in North Dakota first began experiencing symptoms of the drought in November and were labeled a “moderate drought” area by the U.S. Drought Monitor.

According to the drought mitigation center, the conditions in the fall slowly made their way north into Grand Forks County.

On July 26, 2011, the center said North Dakota did not suffer from dry conditions. By March 20, 2012, a majority of the state was considered abnormally dry before cool temperatures and some rainfall came into the region, Bramer said.

July 17, 2012, found the southeast parts of the state in “severe” conditions while the majority was only “abnormally dry.”

Information released Thursday said only 13 percent of the state is listed as not having problems while almost 87 percent is “abnormally dry,” 38 percent is “moderately dry” and 16 percent is “severely” dry.

Today, a percentage of southwest Grand Forks County is listed as, “severe,” with the remainder listed as “moderately” dry.

The drought mitigation center uses data from soil moisture, reservoirs, winter snow, ground water levels, crop reports, satellite information, among others in its determination.

“We don’t see a clear-cut line,” Fuchs said of the data maps. “But we have a spectrum of indicators in multiple categories.”


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TJ Jerke writes for the Grand Forks Herald