Dry, warm soils expected to reduce runoff, decrease chances of flooding
The NWS in Bismarck issued a flood potential outlook Thursday, March 9.
JAMESTOWN — Even with the area receiving more snow than average this winter, the latest flood potential outlook says dry and warm soils are expected to substantially reduce runoff during the spring-melting season, decreasing the potential of flooding.
The National Weather Service in Bismarck issued a flood potential outlook Thursday, March 9, for March 11 through June 9 that says the James River and Pipestem Creek above Jamestown remain at a slightly below to near-normal risk of flooding. The outlook says the risk of flooding rises for areas below Interstate 94 to slightly above normal at LaMoure on the James River.
The NWS in Bismarck will update the flood risks on March 23.
Jamestown has received 67 inches of snow from November to 6 a.m. Friday, March 10, according to measurements taken at the North Dakota State Hospital. According to the State Hospital’s data, Jamestown received 13 inches of snow in November, 27 inches in December, 3 1/2 inches in January, 3 inches in February and 20.5 inches in March as of 6 a.m. Friday.
The Jamestown area typically has around 39 inches this time of year, said Allen Schlag, hydrologist with the NWS in Bismarck.
More snow was expected in the Stutsman County area Friday and Saturday, March 10-11. A blizzard warning was issued Friday morning from midnight through 4 p.m. Sunday for Burleigh, Dickey, Foster, Kidder, LaMoure, Logan, McIntosh, McLean, Sheridan, Stutsman and Wells counties. The NWS forecast for Friday and Saturday called for 5 to 11 inches of snow.
Most of Stutsman County is abnormally dry, meaning the areas are not in drought but are experiencing abnormally dry conditions that could turn into drought or are recovering from drought but are not yet back to normal, according to the U.S. Drought Monitor.
The flood potential outlook says dry and warm soils are still expected to substantially reduce runoff from melting snow under all but the most extreme conditions, including a scenario of rain on snow.
“When I start talking about extreme melt conditions, I’m talking about … today we are in the 20s and tomorrow we are in the upper 40s and the day after that we are 55 degrees with rain. That’s a pretty extreme melt pattern,” Schlag said.
Because of last year’s dry conditions, the soils are very warm and very dry underneath the existing snowpack, he said. He said the soils from 2 to 5 inches below the bottom of the snowpack are above freezing temperatures.
“That is fairly incredible for this time of year,” Schlag said. “Normally we are looking at frost depths that go down to a minimum of 16 inches, more likely an average of between 24 and 30 inches, and then really severe winters, we will see frost depths in the Jamestown area go down to maybe 4 feet, 48 inches or better.”
Since the Jamestown area had 13 inches of snow in November, he said the snow insulated the soil from the very low temperatures in December.
“When we finally get into the spring melt season here, and we start seeing melt water being generated from that snowpack, our expectation is that a large fraction of that is going to go right into the dry and warm soils,” he said.
Currently, a good portion of the James River Basin has a snow-water equivalent of 4 inches, but some places south of Jamestown have more, Schlag said. He said Marion has a snow-water equivalent of more than 6 inches and other places have close to 7 inches.
“All we’ve seen since then is more snow, so there is a large water content in the existing snowpack,” he said.
The flood potential outlook says the region has experienced well below-normal temperatures for quite some time. Depending on the area, temperatures in December were about 10 degrees below normal, Schlag said. But he said temperatures in January were above normal and February had slightly above-normal temperatures.
“For the last couple of weeks we’ve been cooler than normal, and that is the expectation going forward is that we are going to stay cooler than normal going forward for … the foreseeable future,” he said. “ … The spring, it sure looks like we are going to stay cool well into the middle, maybe the latter part of spring.”
He said March is the month when outlooks of spring melt are initiated. He said March is historically the month when temperatures rise quite a bit. For example, he said Bismarck's average high temperature on March 1 is around 30 degrees but rises to about 49 degrees on March 31.
“At this juncture in the game, cooler than normal still includes temperatures that will encourage melting of snow,” he said.
As summer hits the region, there is an increased chance for an El Nino climate pattern to move into the U.S. and for the La Nina to move out, Schlag said. He said the El Nino climate pattern historically produces a daily warm and dry pattern for much of the U.S.
During El Nino, warm water pushes toward the West Coast of the U.S., causing the Pacific jet stream to move south of its neutral position, according to the National Oceanic and Atmospheric Administration. The NOAA says the shift causes areas in the northern U.S. and Canada to be drier and warmer than usual.
During La Nina, warm water gets pushed toward Asia, causing cold waters in the Pacific Ocean to push the jet stream northward, according to the NOAA. The NOAA says the northern U.S. and Canada tend to be wetter and colder during La Nina winters.
The La Nina climate pattern has been in the U.S. for the third consecutive year, which is an “enormous rarity,” Schlag said.