Wednesday storm: Grazes metro, heavier snow S & E

The forecast models are getting a better handle on snow prospects for Wednesday, and it looks like a glancing blow for the metro.

Here's the latest thinking, and my forecast snow totals as of Monday for our Wednesday system.

The system:

A moderately strong low pressure system will form in the Texas Panhandle early Tuesday and begin to track northeast.

The track:

The last few model runs are coming into closer agreement on a more southerly track. This would take the surface low from the Texas Panhandle early Tuesday, then south of Kansas City Tuesday evening to near Chicago by Wednesday evening.

This southerly track should place the heavy snow band in northern Iowa, southeast Minnesota and central Wisconsin. It appears the Twin Cities will be on the northwest edge of this system, meaning any further southward shift in the low track could mean snowfall misses the metro.

Timing:

Look for snow to spread north during the day Tuesday in Iowa and into southern Minnesota later Tuesday night. It appears snowfall that does reach the metro will not get here until after midnight Tuesday night/ Wednesday, making this a mostly Wednesday system.

Snowfall should continue (with peak intensities) much of Wednesday south and east of the metro, but snow may end by 6pm in the Twin Cities. The event duration should be under 12 hours in the metro, with a longer period of snowfall to the south and east.

Snowfall totals:

The storm is still nearly 40 hours away, but I think we have a handle on some projected snowfall totals with this system. It appears the heavy snow band with this storm will set up through Ames, Decorah, Albert Lea, Rochester, La Crosse, Tomah, Eau Claire to Wausau.

NAM lays out heavy snow band through Iowa, SE MN & Wisconsin.

If you are in or planning travel to southeast Minnesota, Iowa or central Wisconsin

(I-35 south or I-94 east) late Tuesday night and Wednesday expect heavy snow in those areas.

Heavy snow band: 6" to 10" possible (Ames, Mason City, Decorah, Albert Lea, Rochester, La Crosse, Tomah, Eau Claire to Wausau.)

Further north & west: 2" to 5" This includes a swath from Mankato through the far SE metro to Hinckley and Duluth.

Northwest fringe of storm: 1"- 3" possible. This includes a swath from near New Ulm to Glencoe into the northwest half of Twin Cities, St. Cloud Lake Mille Lacs into the Iron Range.

The best snowfall "range" for the metro looks like 1" to 4" with the best chance of 4" in the southeast metro near Hastings and Lakeville, 2" to 3" in the central metro and closer to 1" in the northwest. The NAM & GFS are printing out 2.5" for MSP Airport Wednesday. That seems like a reasonable snowfall total to me at this point barring any track changes. Expect some variation in model snowfall output between now and Wednesday.

*Again any further southward shift in track could reduce snowfall totals accordingly.

Bottom line: Expect snow after midnight Tuesday night/Wednesday. Snow should taper by around 6pm Wednesday in the metro, but will last into the night to the east into Wisconsin. The heaviest snow band will likely set up south and east of the Twin Cities.

NAM prints out 2.5" for MSP Airport Wednesday.

Impacts:

It looks like Wednesday morning rush hour could be the first to be impacted by the snow in the metro. Travel south (I-35) and east (I-94) will become difficult all day Wednesday as the storm ramps up. While I do not expect any "blizzard" conditions, there will be winds of 15 to 25 mph with this system, and it will produce some blowing and drifting in open areas.

Storm character:

This will be a relatively wet snow compared to many of the storms we've seen this winter. Snow:water ratios should be between 9:1 and 12:1 with this storm.

Temperatures will be in the low to perhaps mid-30s with the system Wednesday. Roads may be slushy at times, but compacted snow in many areas will make for slick travel.

This will be a classic wet slushy early March storm in many areas. There could be "thundersnow" in southeast Minnesota and Wisconsin with this system.

Additonal snow "chances" Friday night & Sunday night?

A note on forecasting snowfall in advance of storms.

This is the first actual snowfall "forecast" with projected totals I've made for this system. There are very good reasons why it's prudent and responsible to wait until 24 to 48 hours prior to an event to make snowfall forecasts.

-The medium range forecast models may identify the possibility of a storm a week or more in advance, but the errors are just too great 3 to 7 days out to make accurate, reliable or useful snowfall projections.

-Models don't really "lock on" to approaching storms until they track into the North American upper air (weather balloon) and surface observation network. The higher data density provided by the network allows better "sampling" of the storm properties as systems move ashore, and leads to better track and intensity forecasts.

-Model accuracy for snowfall totals in Midwest storms improves in accuracy dramatically within 48 hours of a storm.

-There is a window in which improved forecast accuracy and the need to plan and take effective action for an approaching storm meet. 24 to 48 hours in advance of a snow event is still plenty of time for most people to plan accordingly for the coming event.

Issuing specific (& likely unreliable) snowfall forecasts several days in advance can result in wild forecast ranges (2" to over a foot?) which are ultimately of little "value" to weather consumers.

Taste of Spring: A shot at 40 Thursday & Friday?

It looks like the weather will mellow and turn milder with a taste of spring Thursday into Friday. Thursday should feature plenty of bright, strong March sun, with temps making a run through the upper 30s to near 40 in southern Minnesota including the metro.

A surge of milder air Friday may help temps push into the lower 40s Friday, before another cold front (with a few rain and snow showers) brings us back to March reality this weekend.

Let's see what the next set of model runs does with the system today and tonight, and enjoy a quiet Monday and Tuesday!

PH