Forecasts in flux for Monday’s snow storm

Update 11:15 pm Sunday evening

Late evening (0Z) GFS run is in. It's sticking with the notion of an overall 4" to 8" metro snowfall range, and a further southeast storm track. Let's see what the morning model runs, satellite and radar trends reveal.

*Update 9:10 pm Sunday evening

The late evening (0Z) NOAA NAM model run has upped the ante significantly on metro snowfall potential. The NAM is cranking out 12" to 18" snowfall totals very close to, if not in the Twin Cities area.

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Keep in mind the NAM can be overly aggressive with snow totals. It's also just one model and one run, but a couple of other models support the idea of more snow for the metro. Awaiting tonight's GFS run for a sanity check in the next two hours.

Stay tuned for possible forecast changes.

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Twin Cities NWS

There's still a lot we don't know about Monday's impressive looking inbound winter storm.

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NOAA

Here's a breakdown of what I think is highly likely, and what we still don't know.

What we know with high confidence

  • Winter storm warnings are in effect for southeast Minnesota and western Wisconsin. (100%)

  • Winter storm watches include the Twin Cities metro and may be upgraded to warnings. (100%)

  • Widespread snowfall and wintry travel conditions develop Monday afternoon and evening. (100%)

  • A strong low pressure system heads for Chicago-Milwaukee late Monday night. (95%)

  • The precise storm track is still uncertain. (95%)

  • Heavy snow will fall on the northwest side of the storm. (100%)

  • The heaviest snow band of 6" to 12" will likely center either side of an Albert Lea-Rochester-Winona-Eau Claire axis. (75%)

  • The Twin Cities metro rides the northwest edge of the heavy snow zone to the southeast. (75%)

  • Lesser totals are likely in the Twin Cities, especially the northwest metro. (75%)

  • Snow will spread from south to north Monday afternoon in southern Minnesota. (85%)

  • Snow should arrive in the Twin Cities late Monday afternoon or early Monday evening. (80%)

  • The heaviest snowfall should occur Monday night. (90%)

What we still don't know - lower confidence forecast parameters

  • Precise storm track still uncertain. Models have show a slight southeast trend shift.

  • Twin Cities on the edge of heavy snow zone to the southeast. (60%)

  • Metro snowfall totals still uncertain depending on storm track.

  • Best metro estimate seems to be 4" to 8" at this time. (65%)

  • Those totals could fall some (2" to 6" range) if storm shifts any further southeast. (25%)

  • Heaviest snow totals likely in southeast metro, less northwest. (60%)

NOAA supercomputer
NOAA supercomputers

Searching for consensus

Meteorologists want consensus in model forecasts. Forecast models are a little like people. Everyone has an opinion, and a bias. I don't need 60 different models with 60 different answers. Most times I just need one trustworthy model I can count on, who's biases I understand.

NOAA's NAM model is not always the most reliable in snow. It tends to have a northward bias. It's on the high end of snowfall totals for the metro with around 8+". NOAA's GFS has trended further southeast with this system and paints a picture of closer to 5".

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NOAA via Iowa State University

The ECMWF (Euro) model has done especially well with the past two storm systems. The usually trusty Euro is cranking out about 7" for MSP.

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Norwegian Meteorological Institue

The reasonable forecast at this point seems to be a metro snowfall range of 4" to 8" with the heaviest totals favoring the southeast metro. The "bust" scenario is that the storm track shifts even further southeast, and snowfall totals in the metro drop into the 2" to 6" range. I give that about a 25% chance of happening.

Here's the latest Twin Cities NWS view. They have trimmed metro totals slightly base on the southeast shift.

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This is why meteorologists get prematurely gray.

Bottom Line: Be prepared for snow Monday night into Tuesday. Slick roads and difficult winter travel will be widespread across southeastern half of Minnesota, northern Iowa and western Wisconsin.

Stay tuned for updates.