More snow and rain! Spring flooding potential worsens
As Minnesota’s snowpack deepens, weather officials are fretting the spring thaw.
With lots of snow on the ground and more on the way, Minnesota weather officials are looking with increasing trepidation toward the spring thaw, with better-than-even chances of “major flooding.”
When it comes to flooding potential, it’s all about snow depth, saturation, and how quickly it melts.
Up until February, Minnesota had seen a relatively snow-free winter. But then a series of vortex blasts hit the region, blanketing it with record-breaking accumulation for the month.
The end result: February snow depths are solidly in the top 10 on record, as of Feb. 28. Especially in key regions that feed into the Mississippi and St. Croix rivers.
Take Minnesota’s Mississippi headwaters region. Grand Rapids, as an example, had 26 inches — putting it in a tie for the fifth highest on record. St. Cloud had 21 inches, its eighth deepest on record. Along the St. Croix River, St. Croix Falls had 18 inches of snow — its fourth highest on record. The Twin Cities region is also in the top tiers. At the Minneapolis-St. Paul International Airport, they had 16 inches — the sixth highest on record.
The National Weather Service said in a report released Thursday, Feb. 28, that substantial snowpack in late January and February means that “widespread, above normal” runoff is now likely, with ultimate levels likely to depend on the rate of runoff and precipitation in March.
The February snow cover in Minnesota was 5 inches above the 13 inches that was on the ground in February 1965, the year of some of the most damaging floods in southern Minnesota history.
Another punch of heavy wet snow hit Saturday and early Sunday; more than enough to shovel and plow. A significant storm system brought heavy snow and hazardous travel over the weekend. Springfield received 1.27 inches precipitation Saturday — .78 inch in rain and .49 inch that came from 4.1 inches of very wet snow, according to local weather observer, Russell Rogotzke.
In its latest spring flood outlook on March 7, the National Weather Service drew a grim picture for potential flooding. They noted that precipitation (the water equivalent in snow) in February was 200 to 400 percent above normal.
“Depending on spring precipitation and temperatures in the coming months, we may see a rapid melt of the snowpack, leading to widespread flooding,” the NWS reported.
It said the continued snowstorms across the Upper Midwest have left the region with a water content in the snowpack of up to 6 inches across much of Minnesota.
The NWS said models show a continuation of colder-than-normal temperatures across the entire region and there is a likelihood of above-normal precipitation through this month.
“This outlook suggests we may see a delayed snowmelt from these colder-than-normal temperatures in March.” They said the pattern for April and May shows normal temperatures and precipitation patterns.
Perhaps the only good news for flooding potential is that the frost is not very deep into the ground, meaning that it will thaw out relatively quickly once the snowcover disappears, allowing the soil to absorb some of the rain in the spring. But on the downside, the soil was heavily saturated last fall, leaving the ground less able to absorb snowmelt and rain.