Here is a wire service rundown of spring flood risk assessments from Midwestern National Weather Service offices released late last week. The forecast appears to be a bit too optimistic, which I detail in some comments following the article.--Bryce
Midwest faces minimal risk of spring floods
JIM SALTER Associated Press
ST. LOUIS (AP) --- Despite the snow still covering the upper Midwest, National Weather Service experts are optimistic that come spring, flooding will be minimal in the nation's Heartland.
Several Midwestern branch offices of the National Weather Service released spring flood outlook reports late Thursday. None project significant flooding--- even the risk of minor flooding is below normal in many places.
That's a bit of a surprise considering how snowy the winter has been. Parts of Minnesota, Wisconsin and Iowa still have up to 3 feet of snow on the ground.
The snowfall has been offset by unusually low river levels and drought, National Weather Service hydrologist Mark Fuchs in suburban St. Louis said. He said that when the snow melts, much of it is expected to go into the parched ground.
"There is a fair amount of snow up north but there is also a drought up north," Fuchs said Friday. "That's the one thing that's going to mitigate the flood potential."
Long-term rainfall projections call for around average precipitation in the spring. Fuchs said if that's accurate, minor flooding could be expected in parts of the Mississippi River from southern Iowa to the Missouri River confluence near St. Louis. Mississippi River tributaries could also see mostly minor flooding.
Some rivers in Missouri, Illinois and Indiana are already out of their banks, though the flooding is expected to be minor and brief.
This week's unusually warm temperatures caused significant snow melt in northern Missouri. Combined with up to an inch of rain in the middle of the week, a few rivers spilled over their banks. Ewing, a tiny community about 120 miles north of St. Louis, was hardest hit, but damage was mostly limited to farmland and county roads.
Spring flood predictions for the region south of St. Louis are difficult to project because the National Weather Service hasn't yet developing flood modeling for the Missouri River, which plays such an important role in Mississippi River depths below the confluence.
The spring outlook from the weather service's Sioux Falls, S.D., office calls for a lower than normal chance of flooding over much of the Dakotas and into Nebraska. The Des Moines, Iowa, office projects near-normal flood risks over most of Iowa, saying that below-normal soil moisture offsets deep frost that often raises flood concern.
The Rock Island, Ill., weather service office projects near-normal flood risk on the Mississippi River in most of Iowa and Illinois, but a slightly elevated risk from Dubuque, Iowa, south to the far northeastern Missouri.
Fuchs cautioned that a strong and extended storm or two could wipe out all the hopeful predictions.
"The bottom line is how much rain do we get," he said.
It looks as if this forecast is too optimistic when you consider both the pattern that appears likely to set up for spring and the recent underperforming of the National Weather Service's seasonal forecast. Let's get the recent forecast performance out of the way first--NOAA basically busted on the winter forecast for 2013-14, calling for "equal chances" on both temperature and precipitation for most of the central U.S. We all know what happened since, with the coldest conditions in memory for many, and for those of us with a bit longer memory, the coldest in some 35 years or so, going back to the late 1970s. Winter precipitation has also been much heavier than forecast in the northeastern through southern Midwest as well.
But now to the major reason why it looks to us like such a forecast carries a bit too much hopefulness--the ability of the upper-air pattern to stay cold and stormy. We know that another brutal cold wave is poised to cover the central U.S. during this final week of February, which will do nothing to hasten warming of soils for spring field work. And, of course, late last week saw some bitter-cold air and a swath of heavy snow in parts of the northern Midwest flood concern area as well.
The thing is, this week's cold wave does not appear to be the end of the chill. Forecast maps for the first part of March have a big, broad upper-level low (trough) sprawled across the Canadian Prairies, with the southern edge of that trough--or, in other words, the boundary between the cold northern trough and milder upper-atmosphere high pressure (ridge) in the southern U.S.--running through the north-central U.S. between Interstates 80 and 90--the Iowa-Minnesota corridor. In air-mass discussion, the term "boundary" is code for "surface front". And, with such a big difference between cold north and warm south, that frontal presence gives a strong hint at stormy conditions--rain, snow, possibly sleet the way this winter season has been.
The point is, there is every indication that the atmospheric patterns that we have been dealing with for quite some time now are going to stay with us--and their performance gives a strong reason to be concerned about spring flood chances being more than "minimal" in Spring 2014.
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