Rain expected to change to snow; cold temperatures on the way

It seems that there would be no problem this far north, this late in December, to expect snow over rain, but the climate it is a-changin'.

A steady rain fell much of the day over the landscape of central and southern Minnesota. It was even raining as far north as Crane Lake late this afternoon.

If the precipitation had fallen as snow we would likely have accumulated an inch or two increasing the odds of a white Christmas.

As I read the National Weather Service forecast discussion I found myself in agreement with their assessment of the short term forecast. There is a general consensus of uncertainty of snow accumulations tonight and Tuesday. I present this graphic of the National Weather Service's latest thinking.

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The Weather Prediction Center paints this graphic of the probability of greater than two inches of accumulation  later tonight and Tuesday.

prb_24hsnow_ge02_2014122300f024
Image:Weather Prediction Center.

The track of the surface low coming out of Iowa through southern Wisconsin would typically favor a nice snow accumulation from Mankato to Hayward, but we are challenged by the new normal. The timing of the precipitation changing to snow will determine snow amounts.

kowtrack
Forecast low pressure track from the National Weather Service.

Precipitation is fractured with this system and essentially the rain will change to snow directly overhead, rather than from west to east.

Here's the how the National Weather Service in Duluth expects the snow to play out:

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE DULUTH MN

336 PM CST MON DEC 22 2014

...ACCUMULATING SNOW EXPECTED OVER PORTIONS OF NORTHWEST

WISCONSIN LATE TONIGHT THROUGH TUESDAY NIGHT...

.A LOW PRESSURE SYSTEM WILL MOVE ACROSS THE UPPER MIDWEST TONIGHT

THROUGH WEDNESDAY AND BRING ACCUMULATING SNOW TO PORTIONS OF THE

NORTHLAND. SNOW WILL DEVELOP OVER NORTHWEST WISCONSIN TONIGHT...

AND CONTINUE THROUGH MUCH OF TUESDAY BEFORE DIMINISHING TUESDAY

NIGHT. THE AXIS OF GREATEST SNOWFALL ACCUMULATIONS...3 TO 5 INCHES

IS EXPECTED OVER PORTIONS OF NORTHWEST WISCONSIN.

This screen capture of regional radar from just before 4:30 p.m. CST shows the rain changing to snow (blue color) in central Minnesota.

420pmcpcpn
Radar image 420 p.m. CST. Image:Wunderground.com

Once this system pulls east on Tuesday night, dry conditions are seen for Wednesday and into Christmas day. Temperatures will be slightly above normal for daytime highs.

MaxT3_minnesota (1)
Maximum temperatures on Thursday.

Historical data puts the odds of a white Christmas well above 50 percent in the Twin Cities. The State Climate Office of Minnesota presents this statement:

In 115 years of snow depth measurements in Twin Cities, a white Christmas happens about 72% of the time.

white_xmas
Image:Minnesota Climatological Working Group.

I'm thinking the odds of one inch or more of snow on the ground in Minneapolis-St. Paul on Christmas morning is about 50 percent.

Nationally, the National Oceanic and Atmospheric Climate office presented this graphic of the historical probabilities of a white Christmas:

WhiteChristmasProbabilityBinned_620_hat
Image;Climate.gov

The next weather system is something to keep an eye on for Friday as a strong wind maximum in the jet stream dives down the west coast before turning north through the mid-Mississippi Valley.

namUS_500_spd_084 (1)
Jet stream from North American Model valid

Looking ahead to the weekend, arctic air will sink south over the northern states. Much colder temperatures are likely into early next week.

DAY7_MAX_filled (1)
Maximum temperatures forecast for Monday, December 29th. Image:NOAA