Major winter storm shifting slightly north? GFS indicates metro snow potential

Major Winter Storm still on track for southeast Minnesota, Iowa & Wisconsin Wednesday night & Thursday

Slight northward shift? The GFS model (the most reliable with the past 2 systems) now brings several hours of light snow into the metro.

6″ to 12″ heavy snow band still likely south from Des Moines to La Crosse & Tomah

Tuesday Clipper: some 2″ to 4″ snowfall totals in southern Minnesota Tuesday with productive “I-90 Clipper”

PUBLIC INFORMATION STATEMENT

NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN

336 PM CST TUE DEC 18 2012

…SNOWFALL TOTALS FROM TODAY ACROSS SOUTHERN MINNESOTA…

SNOW REPORTS LISTED BY AMOUNT

INCHES LOCATION ST COUNTY TIME

—— ———————– — ————– ——-

4.20 1 NE FAIRMONT MN MARTIN 1245 PM

4.00 3 WSW SHERBURN MN MARTIN 1000 AM

3.00 ALBERT LEA MN FREEBORN 1129 AM

2.60 FAIRMONT MN MARTIN 0830 AM

2.00 WELLS MN FARIBAULT 1135 AM

1.90 1 S BLUE EARTH MN FARIBAULT 0805 AM

Updated Twin Cities quick look forecast

207 ql.PNG

GFS: Not soooo fassst?

Some late breaking model trends late Tuesday could cause changes in the metro forecast for Wednesday night & Thursday.

The basic elements remain the same for the Upper Midwest.

-A major winter storm is heading for the Upper Midwest.

-Snow will be widespread in Iowa, southeast Minnesota & Wisconsin Wednesday night and Thursday.

-The heaviest snow band of 6″ to 12″+ looks to be along and surrounding a Des Moines-La Corsse-Tomah-Green Bay line.

-Snow and increasing winds will create difficult to impassable travel conditions in these areas Wednesday night & Thursday.

Metro riding the (snowy?) edge:

All of the models still keep the heaviest snow bands well south & east of the Twin Cities with this system.

Until Tuesday PM, most of the models have kept most all the snow away from the metro.

But Tuesday the GFS showed a trend toward extending the northern edge of the snow shield a little further north…into the Twin Cities Wednesday night & Thursday AM.

207 gfs earl.PNG>

Image: NOAA GFS snowfall output via wxcaster.com

The oft (and appropriately) maligned GFS has been one of the better models with the past few systems coming through Minnesota.

The Euro model is now also indicating some (lighter) snowfall for the metro Wednesday night & Thursday.

Heres’ a look at the liquid moisture (QPF) laid out by the models.

GFS: .18″

Euro .10″ (2.7mm)

The totals are not that impressive, but with cold air around the snow:liquid ratios in Minnesota with this system could be quite high…maybe as high as 15:1 or even 25:1.

25:1 is like winning a long shot at the track.

Here’s what the paltry .18″ of liquid (the going GFS forecast) translates to as snowfall at various ratios.

15:1 = 2.7″

20:1 = 3.6″

25:1 = 4.5″

That could translate into some “shovelable” and even “plowable” snow and greasy roads for parts of the metro…especially the southeastern parts.

207 metty.PNG

Image: Iowa State University

The Twin Cities NWS shows some interest in this trend in their Tuesday PM forecast discussion, especially for southeast Minnesota.

THIS STORM SYSTEM HAS MOVED INTO THE SW U.S. EARLIER TODAY…WITHSNOW ALREADY DEVELOPING IN THE CENTRAL ROCKIES. THE MAIN FORECASTCONCERN IS QPF AMTS WHICH COULD MEAN HIGHER SNOWFALL TOTALS IFHIGHER SNOWFALL RATIOS DEVELOP TO THE NW OF THE STORM SYSTEM. THIS MORNING SYSTEM HAD RATIOS OF 18-1 TO 25-1. EVEN WITH A CONSERVATIVE SNOWFALL RATIO OF 15-1 COULD PRODUCE 3.5 INCHES OF SNOWFALL WITH ONLY A QUARTER INCH OF LIQUID WATER. BASED ON THE LATEST MODELS HAVING AS MUCH AS 0.50 INCHES OF LIQUID WATER BY THU AFTN…THIS WOULD BE EQUAL TO 7.5″ OF SNOW.

If the GFS trend is right, the metro may see a period of light snow from around 6pm Wednesday evening to 6-9 am Thursday. Snowfall under this scenario could produce 1″ to 2″+ for parts of the metro…with 3″+ or more very close to… or possibly sneaking into parts of the metro.

Also higher snowfall totals (6″+) may shift into southeast Minnesota including Rochester, Albert Lea and Winiona. It’s quite possible Twin Cities NWS will expand winter storm warnings northward by Wednesday AM.

Stay tuned as we see what the overnight & Wednesday AM model runs bring, but be aware that the snowfall forecast for the metro may change in the next 12-18 hours.

PH

Comments are closed.