‘Life is like a box of chocolate. You never know what you’re gonna get.’ -Forrest Gump
Yes, April weather in Minnesota is like Forrest Gump’s proverbial box of chocolates. We savor sunny skies and 69 degrees on Monday. And peer out from inside a snow globe Thursday.
And so it goes.
Some distinct forecast model trends emerged Monday for this week’s evolving out-of-season winter storm. There has been a slight southward drift in the storm track. A a slower storm suggests less impact Wednesday, with the bulk of wind and snow Wednesday night and Thursday. A drier air mass feeding into the northern side storm has trimmed snowfall potential.
That said, this still looks like a high-impact wintry weather event Thursday.
Forecast model trends
Monday’s model runs feature later precipitation onset. Forecast model consensus seems to be evolving around a rainy-sleety to snowy mix spreading northward across southern Minnesota Wednesday. That would mean Wednesday morning’s rush hour would see few if any impacts in the Twin Cities.
Heavy and persistent snow bands look likely to set up across southern Minnesota Wednesday night through Thursday. Strong updrafts may initiate convective thundersnow. Snowfall rates of 1-2 inches per hour look possible. Throw in a tight pressure gradient and winds over 40 mph and you’ve got a potentially serious weather situation for most of Thursday.
NOAA’s GFS model captures the essence of the current forecast model consensus.
Snowfall Totals: Still a plie?
The overall trend on snowfall totals has been down Monday. But that’s like saying you only have to jump off a 20-foot cliff instead of a 40-foot cliff.
The American (GFS) and European (ECMWF) models suggest about a foot of snow around the Twin Cities area. Higher totals over 20 inches are still showing up (especially on the Candian model) in western Minnesota in a zone surrounding Canby, Marshall, and Willmar.
It’s still too early for reliable snowfall projections. But the notion of a foot of snow for much of southern Minnesota looks more reasonable by the hour.
Here’s NOAA’s GFS model snowfall output.
Let’s see what tomorrow’s model runs bring.
Models gone wild
Forecast models sometimes wildly overpredict snowfall totals in collar-season storms. The Twin Cities NWS has a great description today of why many in the meteorological community don’t post predictions of 20 to 30+ inches of snow days in advance.
Here’s the excerpt from the Twin Cities NWS forecast discussion.
One element that most don`t understand about models and the output
of high snowfall totals well in advance of the storm, is the fact
of seasonal variation of snowfall ratios, and the added affects
of higher sun angle and a warm ground cause errors/unrealistic
values. Therefore, models try to forecast snowfall amounts of 20
to 40 inches, but you need to deal with the possibility of mixing
of other precipitation types, rates, time of day and the overall
isolation during the daytime period per ground type (grass vs.
concrete, etc). Snowfall amounts through Thursday evening look to
range from nearly 20 inches over west central Minnesota, where
local terrain could lead to higher totals, to around 6 to 17
inches where the current Winter Storm Watch has been issued.
Winter storm watches
The winter storm watch has been expanded to include the Twin Cities starting late Wednesday.
Including the cities of Morris, Glenwood, Madison, Benson,
Montevideo, Willmar, Litchfield, Granite Falls, Olivia,
Hutchinson, Gaylord, Redwood Falls, New Ulm, and St Peter
442 PM CDT Mon Apr 8 2019
…WINTER STORM WATCH REMAINS IN EFFECT FROM WEDNESDAY EVENING
THROUGH FRIDAY AFTERNOON…
* WHAT…Blizzard conditions possible. Total snow accumulations of
greater than 8 inches possible along with widespread blowing and
drifting snow. Winds could gust as high as 55 mph.
* WHERE…Portions of central, south central, southwest and west
* WHEN…From Wednesday evening through Friday afternoon.
* ADDITIONAL DETAILS…Travel could be very difficult to
impossible. Areas of blowing snow could significantly reduce
visibility. The hazardous conditions could impact the morning
or evening commute.
April snow events
Minnesota is no stranger to heavy April snow events. Last year we recorded two of the top 10 April snow storms.
A look back at historic April snowstorms in Minnesota – Remember last year? The Twin Cities saw two significant storms (April 2-3 & April 13-16), and both made the top 10 list for largest snowstorms in April. Additional info: https://t.co/HgCekUUf4y #mnwx #snow pic.twitter.com/sFgsElUSze
— NWS Twin Cities (@NWSTwinCities) April 8, 2019
The big melt
The good side of April snow? It doesn’t last long. Most of it should be gone next week.