Friday snow: Winter storm watch posted

Get ready snow fans. We're roughly 48 hours away from the next significant winter storm in the Upper Midwest.

Winter storm watches are posted as of this morning.

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN

405 AM CST WED DEC 14 2016

...DANGEROUS WIND CHILLS EXPECTED TONIGHT INTO THURSDAY MORNING...

...SIGNIFICANT SNOWSTORM POSSIBLE FRIDAY AFTERNOON THROUGH SATURDAY MORNING...

TEMPERATURES BETWEEN 10 AND 20 DEGREES BELOW ZERO ALONG WITH 5 TO 10 MPH WINDS THROUGH THE NIGHT WILL PRODUCE DANGEROUSLY COLD WIND CHILLS OF NEAR 25 TO 30 DEGREES BELOW ZERO ACROSS ALL OF CENTRAL AND SOUTHERN MINNESOTA AND WESTERN WISCONSIN.

SNOW WILL OVERSREAD THE AREA DURING THE DAY FRIDAY AND BECOME HEAVY FRIDAY AFTERNOON INTO FRIDAY NIGHT BEFORE TAPERING OFF SATURDAY MORNING. SNOWFALL AMOUNTS IN EXCESS OF 6 INCHES ARE EXPECTED WITH THIS STORM. THE RISK FOR SEEING 6 OR MORE INCHES IS GREATEST ALONG AND SOUTH OF A LINE FROM BENSON...TO CAMBRIDGE...TO LADYSMITH WISCONSIN...WHERE A WINTER STORM WATCH IS NOW IN PLACE FROM FRIDAY AFTERNOON THROUGH SATURDAY MORNING.

Cold first

Another Arctic front races south across Minnesota today. You'll notice the winds picking up, as wind chill values fall through the day and especially this evening. Watch temperatures plunge behind the front and bottom out around -10 in the Twin Cities and closer to -20 up north by Thursday morning.

The Arctic high pressure cell glides over the Upper Midwest Thursday. The first band of light snow develops as warmer air pushes north ahead of the next storm system late Thursday night into Friday morning. The main event gathers to the west.

Southerly storm track

Today's early forecast models still favor a southerly storm track south of Des Moines and Chicago. That should lay the heaviest snow bands out south of the metro in southern Minnesota and Wisconsin. Milder air overrunning the cold dome should still favor significant snow for the Twin Cities. Here's the GFS model version of events.

Efficient snow maker

With plenty of cold air to work with, Friday's snow system will be another efficient snow producer. Snow to water ratios will run in the 16:1 to 18:1 range once again. That means another light fluffy snowfall that can pile up inches over time.

The overnight Euro cranks out .44" liquid for MSP. That's 7 inches of snow at a 16:1 snow to water ratio. NOAA's GFS is leaning lighter, closer to 4".

In all honesty it's still to early to express high confidence in snowfall totals. But at this early phase the guidance would seem to suggest a general 4" to 8" range for the metro is probably the most likely scenario, with the potential for 6" to 12" across southern Minnesota and Wisconsin.

Two different scenarios here. Here's NOAA GFS model on the lower end of guidance, a 3" to 5" snow shot for the Twin Cities.

Here's the same model but with so called Kuchera method, which accounts for a higher snow to water ratio. This is on the high end of guidance, approaching 8" to 9" for the Twin Cities with some prolific totals south.

Bitter weekend blast: A shot at -20 in Twin Cities?

One thing for sure, the coldest air of the yet young winter season arrives behind the storm this weekend. Both the Euro and NOAA's GFS are cranking out temps colder than -20 for MSP by Sunday morning.

Air temps of -25 close to the metro by Sunday morning? We'll see if it gets that cold, but I think -20, and the coldest air mass in nearly 3 years is a real possibility.

50 degrees warmer next week

A progressive Polar Vortex means a glancing blow of the worst of the sub-zero cold this time. After about 36 hours of sub-zero pain Sunday and Monday, temperatures moderate quickly as Pacific flow returns next week.

Temps should make the lower 30s again by next Wednesday and Thursday. It may feel downright tropical around here after this weekend's bitter blast.

Hang in there Minnesota.