The outlook for spring flooding is pretty likely in much of South Dakota, according to the National Weather Service report issued last week.
Pierre and Fort Pierre are right on the edge of the area with the most potential for spring flooding, with little or no snow cover to the west and southwest, mostly, but significant snow cover to the north and east.
“You guys are sitting pretty good out there,” is how Amy Parkin put it on Sunday, about Pierre and Fort Pierre.
Parkin is a lead forecaster at the National Weather Service office in Aberdeen. On Sunday, Feb. 16, she was looking the colored maps showing snow depth and snow/water equivalence across the state that were issued Feb. 13 by the weather service.
On the snow depth map, Pierre and Fort Pierre are touching an area of red to the northeast that indicates snow depths of 2-4 inches. To the southwest of the sister cities, is white on the map, which indicates — maybe with irony — no snow cover to speak of.
In large part, because of the very wet conditions across eastern and central parts of the state last year, the outlook for flooding this spring is above normal, Parkin says.
“The James River has been above flood stage all winter, it froze above flood stage,” Parkin said of the main waterway that goes through Aberdeen and by Redfield and points southeast. “That’s much wetter than normal.”
It means, the saturated soils around it and the flooded stage of the river already, as well as snow depths now of 16 to 30 inches around Redfield, that there is a greater than 95 percent chance of major flooding there between now and May 15, according to the weather service’s outlook, Parkin said.
Meanwhile, the Bad River that empties into the Missouri River at Fort Pierre after its long, wending way from the Black Hills, has less than an 8 percent chance of minor flooding and less than a 5 percent chance of major flooding, Parkin said.
Parkin said there is no sign of major storms bringing any precipitation to the area over the next week.
The weather service’s Spring Flood Outlook, which gives a different level of prediction than more near-term forecast, says of the state: “The outlook for the next two weeks is for higher chances for below-normal precipitation and for higher chances for above-normal temperatures. The 90-day outlook through the end of April shows higher chances for above-normal precipitation and temperatures.”
Per usual, the Black Hills is its own kind of weather area and it has much more snow and snow-water equivalent than the rest of western South Dakota.
“There are 40 inches or more of snow over parts of the Hills,” Parkin said. The water-equivalent of that snow ranges from 8 inches to more than a foot, according to the weather service’s maps.
Just what happens flood-wise this spring across the state depends, as always, on how much precipitation falls from now until then, and the pace of the spring melt.
The soils that were saturated pretty much all of last year haven’t done much drying out over the winter, Parkin said.
“If they are fully saturated like they were last fall, that’s the way the freeze and they just stay in that frozen state,” until spring thaw, whether fast or slow, depending on the weather, Parkin said.
Frost depths are mostly in the range of 1 foot to 2.5 feet. The fact the soils across much of the state froze up in such a saturated states “will make them much more impervious to soaking up much of the snow melt as it occurs,” according to the Spring Flood Outlook.