The National Oceanic and Atmospheric Administration (NOAA) released its spring 2014 flood outlook this week -- and to I'm sure no one's surprise, it calls for a moderate risk in the mid-Mississippi Valley, lower Missouri Valley, Red River Valley of the North, portions of the Great Lakes, and the Black Hills of South Dakota. That's a big chunk of country to have such a forecast.
A conference call that I listened to about the spring forecast for the NOAA Central Region this week highlighted this situation. In fact, Jim Angel, Illinois State Climatologist, suggested that a theme song for the conference call might be a classic jazz hit sung by Ella Fitzgerald that is titled "Spring Will Be A Little Late This Year."
The big reason for this large moderate-level flood risk is, of course, the harsh winter we've seen in the central and eastern U.S. NOAA's description of the situation notes that this winter season "...produced an above normal amount of water in the current snowpack and a deep layer of frozen ground much further south than typical. With significant frozen ground in these areas, the flood risk is highly dependent on the amount of future rainfall and the rate of snowmelt this spring." These factors, along with expected seasonal spring temperatures and rainfall, are the reasons behind the moderate flood risk for southern Wisconsin and southern Michigan, along with portions of Iowa, Illinois and Indiana.
In the lower Missouri basin across much of Missouri, there has been some minor flooding already. The NOAA forecast notes that "flood potential will be driven by individual convective rain storms typical in the spring." I would add that convective rain storms are produced many times by dynamics associated with a cold air-warm air frontal boundary. This is a hint that the cold north (Canadian Prairies-origin chill) may actually set up precipitation events that lead to heavier rains than expected and could up the ante on flooding in the Mississippi and Ohio valley basins as well.
(A big detail here -- NOAA said that the "large quantity of water in this remaining snowpack is highly unusual for this time of year.")
For the Red River valley of the North, along with the Souris River in North Dakota, moderate risk for flooding is due to river ice jam issues along with significant frozen ground. In the Black Hills region of South Dakota, saturated soils comprise the main reason for moderate flood risk. It should be noted that there is limited snow cover in this area.
(By the way -- as of Thursday, March 20, 2014, there was an 80 percent chance of exceeding moderate flooding at Fargo, N.D., and a 45 percent chance of Fargo exceeding major flooding.)
There is also a great deal of interest in what the situation will be for flooding in the upper reaches of the Missouri from Montana into North Dakota. In this area, minor flood potential is indicated, but NOAA also notes that "A potential for exceeding minor flood levels exists for the northern Rockies and northern Great Plains in portions of Montana and Wyoming. Wet soils and high river levels prior to the winter freeze combined with above average mountain snowpack are the drivers for this flood risk. Localized flooding due to ice jams has already occurred, and will remain a threat through the spring thaw."
So, the refrain "Spring Will Be A Little Late This Year" comes back again.