Updraft: December 12, 2012 Archive

Moderating temperatures; warm enough for liquid precipitation

Posted at 6:22 AM on December 12, 2012 by Craig Edwards
Filed under: Rainfall, Winter 2012-13

It's that time of year when surges of arctic air into the upper Midwest battle it out with a return push of milder air from the central plains. Temperatures can climb nicely, particularly where the landscape is free of snowcover.

Snow depth in inches for December 11th:

Source:NOAA

There will be melting snow in southern Minnesota today as temperatures top out in the upper 30s. At daybreak temperatures were already near 20 degrees in the Twin Cities, where peeks of sunshine today will boost temperatures above the thawing point.

Patchy cloud cover invaded the upper Midwest during the nighttime hours. What a difference cloud cover can make to halt raditional cooling from snow cover, especially when accompanied by a moderate push of milder air. St. Cloud saw the temperature rise from 8 below zero before midnight to 12 above by 6 a.m.

Enhanced IR satellite image from 530 a,m. CST. Colder, high cloud tops shown in light blue. Light snow was moving across far northern Minnesota this morning:

Source:NOAA/Unisys

A couple inches of fresh snow can be expected in far northern Minnesota this morning. There is a chance for a ribbon of light snow to fall in northern sections of Minnesota later tonight as well.

Good news for motorists! Warmer temperatures today will partner with the chemicals to melt some of the ice on the heavier traveled roadways. It will take a little longer to see bare/wet pavement on the side streets.

Today's expected high temperatures:

Source;NOAA/NWS

We are still tracking the potential for snow and a mixture of rain and snow for Friday night and Saturday. Precipitation amounts and type are still questionable due to the uncertainity of the low pressure track and intensity.

Remember the previous blogs have been showing a low center reaching southeast Iowa at dusk on Saturday. Here's the overnight GFS predicting a little faster movement, placing the low pressure center at 6 p.m. Saturday in southeast Wisconsin.

Precipitation could begin late Friday and will continue into Saturday. A refinement to the forecast of rain and possible snow amounts will be a work in progress.

The latest thinking from the NWS forecast staff in Chanhassen for the weather maker moving toward the upper Midwest later in the week:

A bright spot in this approaching system is much needed moisture coming on Friday night to parts of Nebraska and Iowa.

NOAA's forecast of precipitation potential for Friday and Friday night.

Happy motoring. Don't forget to fill up with window washer fluid!

Craig Edwards

Temperature tops 40 in Twin Cities; Saturday's precipitation could be mixed bag

Posted at 4:06 PM on December 12, 2012 by Craig Edwards
Filed under: Winter 2012-13

The thermometer overachieved in southern Minnesota this afternoon. A push of milder air on southwest winds to 25 mph combined with a couple hours of sunshine to boost the mercury to 48 F at Fairmont and 41 F at Minneapolis - St. Paul International Airport.

Lack of snow cover and frozen soil in Iowa allowed the mild south winds to usher in quiet a warmup. Ames, Iowa topped out at 50 F this afternoon. Note on the map below the chilly readings in the teens in northwest Minnesota.

Click on map for larger view. Valid at 3 p.m. CST. Temperatures in red. Wind barbs in knots. Source:NOAA

The milder temperatures melted considerable snow on the side streets. Some refreezing later tonight will result in slick spots. Be cautious when traveling outside the Metro late tonight.

Perhaps the easy part is predicting moisture late Friday and Saturday for much of central and southern Minnesota and Wisconsin. While the storm track looks favorable for snow in the Twin Cities, relatively mild surface and low-level temperatures will result in the potential for mixed rain, snow and freezing rain.

NOAA's precipitation, liquid content, for Friday night and Saturday, issued on Wednesday afternoon.

Based on an estimate of one to eight, for liquid to snow and expecting some of the moisture to fall as mixed rain and snow, I come up with about 4 inches of snow on Saturday somewhere in central Minnesota. We are still a long way from noon Saturday. There will be several computer runs to help define the potential snowfall.

The National Weather Service forecast discussion from Chanhassen this afternoon has this to say about the Saturday's precipitation:

SNOWFALL TOTALS FOR SATURDAY ARE CURRENTLY IN THE 3- TO 4-INCH RANGE FROM THE REDWOOD FALLS/MONTEVIDEO AREAS ON NORTHEAST THROUGH ST CLOUD AND MORA AND THEN EAST ACROSS HIGHWAY 8 IN WEST CENTRAL WI. TWO TO 3 INCHES INDICATED FOR THE TWIN CITIES.

One of the forecast tools is the vertical profile of the atmosphere. The GFS model shows temperatures slightly above 0 degrees Celsius in the Twin Cities at the surface on Saturday morning. If this forecast holds, we could experience a mixture of rain and snow and an air temperature in the lower 30s.

GFS sounding valid at 6 a.m. CST Saturday. If you click on image, reduce to 75% to view temperatures in Celsius. Temperature lines run diagonal.
Source:NOAA and Twisterdata.com

As the surface low tracks from Iowa into southern Wisconsin on Saturday it will carry the bulk of the precipitation east of Minnesota Saturday night.

GFS valid at noon CST. Precipitation from 6 a.m. to noon. Surface pressure pattern and wind with low pressure center in Iowa. Source:NOAA/College of Dupage.

Paul will be back on Thursday to track this weathermaker. A blast of arctic air is not expected to follow in the wake of Saturday's precipitation.

Craig Edwards