Weather, climate and public safety agencies are going all out to keep flood concerns front and center across the north-central United States ahead of spring 2020. The latest round of publicity was issued over the Jan. 24-25 weekend from the NOAA Central Region Operations Center. The bulletin has a dual focus: saturated soils and snow pack.
The following are the text details.
PRECIPITATION AND SOIL MOISTURE
Well-above-normal rain and snowfall throughout 2019 has led to record flooding, record-high river levels, and abnormally wet ground for the winter season across the Missouri River Basin. Through the end of December 2019, the Missouri River Basin has had its third-wettest year in 124 years of modern record keeping. Across the Missouri River Basin, North Dakota, South Dakota, Nebraska and Kansas recorded their top five wettest years (January 2019-December 2019). The Upper Mississippi and Red River basins had their wettest years in 125 years of modern record keeping. In the Mississippi basin, Michigan, Minnesota, the Dakotas, Wisconsin and Illinois had their top five wettest years.
The seasonal snowpack continues to build across the headwaters of the Missouri. The Plains' snowpack across the eastern Dakotas is already at 8-20 inches of snow depth, which is holding 2-3 plus inches of water. Elsewhere across the Plains, the snowpack varies. However, with the potential for below-normal temperatures and above-normal precipitation anticipated for the month of February, there is a chance to increase snowpack in areas that have little to none currently.
In the Upper Mississippi and Red River basins, snow depth as of Jan. 22 was from 10-25 inches, with isolated 30-inch snow depth. Water content ranged from 2 to 8 inches, with highest amounts in eastern North Dakota to the arrowhead of Minnesota and the Upper Peninsula of Michigan.
Overall, the mountain snowpack is running about average at this time. We still have a few months left to accumulate additional snow as we are only a little over halfway through the season.
OUTLOOK (based on the NOAA 90-day forecast)
We are heading into the spring with wetter-than-normal soils and a healthy snowpack, and the latest guidance shows that several rivers and streams are running higher than normal.
The latest 2020 (NOAA) Winter Outlook suggests that odds favor a normal to wetter-than-normal February through April across much of the Upper Missouri River basin, with higher odds farther north. We are also expecting cooler-than-normal temperatures as we head farther north, which could hold on to the snowpack longer into the spring. This increases the chances for a sudden and high-impact thaw in the spring.
INGREDIENTS OF A SIGNIFICANT FLOOD SEASON
A repeat of 2019 is not a guarantee. There is still a lot of time factors that would need to come together before we will know just how bad, or how uneventful it will be.
FACTORS THAT WOULD IMPROVE THE (FLOOD) SITUATION:
A period of dry, warm weather allowing soil to drain and evaporate existing moisture; little to no additional snowfall with no extreme cold snaps; a gradual transition out of winter into spring with mild daytime temperatures and nighttime low temperatures below freezing -- to allow snow to ripen and melt off a little bit at a time.
FACTORS THAT WOULD LEAD TO SIGNIFICANT SPRING FLOODING:
Above-normal snowpack across the basin; a long-lived, widespread cold snap on bare ground that freezes the soil deep below the surface and builds a thick layer of river ice; sudden transition from winter to spring that melts the snowpack rapidly and increases the chance for ice jams on the rivers (this happened with the mid-March bomb cyclone in 2019); a significant rain event on top of snowpack that releases the water in the snow rapidly.
Unusually high streamflow, water levels and abnormally wet soil suggest the following potential impacts for the upcoming spring flood season: widespread ice jams, including on some rivers that are not usually affected by ice jams; widespread major flooding again this spring; delay or prevention of crop planting; long-term soil damage; travel impacts due to road, dam, levee and bridge damage.
Bryce Anderson can be reached at firstname.lastname@example.org
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