Eyeing Thursday night snow chances, Canada snow cover favors wintery forecast

Here comes winter.

That's what virtually all the weather maps are saying as we look forward in the next two weeks. All signs point to increasing cold, and possibly snow in the coming days.

It's no big shocker, and it happens every year around this time. Thursday we cross the one month threshold until the winter solstice on Dec. 21. The sun angle now is as low as Jan. 21, and it just doesn't pack enough power to fend off increasingly cold air masses coming south from Canada.

Speaking of Canada, most of our neighbor to the north is now covered in snow. In the blog today I explain why that's important to our forecast, and why that wintry landscape is coming south.

Speaking of winter, is that snow I see on the weather maps later this week? I'll update our growing chance for turning the landscape white later this week. Here's a hint. It might stick around for a long while this time.

Where's my rake? Where's my shovel??

Nov. 22 - average date of first inch of snow cover in the Twin Cities

Last 50 degree day today?

Get out and enjoy this afternoon if you can. Today and Wednesday may be the last time we see temps near 50 degrees until March.

A milder southerly flow and some filtered sunshine help boost temps toward 50 today in southern Minnesota. The best chance of your car thermometer flashing 50 today in the metro? Probably in Chanhassen or Chaska as warmer air nudges into the southwest metro by 4 p.m.  Pipestone, Worthington and Mankato should enjoy mid-50s today.

The mild air lingers Wednesday, before the next polar front dives south by Thursday.

Thursday night snow?

I'm still watching a system that could bring accumulating snow to Minnesota Thursday night into Friday morning.

The forecast models are spinning up a low pressure system and tracking it toward Chicago by Friday. This is not an ideal track for heavy snow in the metro, but advancing arctic air is notorious for 'paving the way' for advancing cold waves with some snow cover.

The timing looks to favor snow from suppertime Thursday night into early Friday morning. If current trends hold, the heaviest snow would fall either side of midnight Thursday night/Friday morning. If this pans out most of the snow could favor the hours between Thursday afternoon and Friday morning rush hours. Here's the European Centre for Medium-Range Weather Forecasts breakdown on snowfall timing.

It's still too early for a credible inches forecast, but some early trends suggest this may not be '"he big one." Still it could be enough to shovel and maybe to plow for parts of  Minnesota.  Here's the overnight output for snowfall, via the National Oceanic and Atmospheric Administration's Global Forecast System model .

The Twin Cities breakdown for potential snowfall totals still varies from run to run, but most models suggest a few inches possible. Iowa State has a nice way of charting successive model runs snowfall output. This is raw data, but worth looking at.

When to pull the trigger on snowfall forecasts?

Snowfall forecasts are among the most difficult and humbling forecasts we make as meteorologists. Now you know why my hair gets prematurely gray in winter.

My feeling is that it's best to pull the trigger on inches about 24 hours before the snow flies in winter storms. This is usually where the best convergence of model accuracy and useful notice of specific snowfall totals occurs for the general public.

Some forecasters will toss around multiple and ever changing snowfall forecasts days in advance. My experience and training from some of the best snow forecasters I have worked alongside at Chicago's Weather Command and the WGN Weather Center tell me it's important to stay consistent and not issue multiple, sometimes conflicting snowfall forecasts in advance of winter storms.

Some forecasters around the country give probabilities associated with different snowfall ranges. My experience is that this can lead to confusion. So I usually give an overall snowfall range and talk about the most likely alternate scenarios of the forecast goes awry. What happens to snowfall totals if the surface low track shifts or the dreaded dry slot moves in, etc?

It is interesting to note that an area as large as the Twin Cities metro often receives snowfall ranges of several inches in individual storms. The 'Domebuster' snowfall range was literally from near 10 inches to around 20 inches across the Twin Cities.

Forecasting a snowfall range indicates two things.

First, we expect a variation in snowfall totals across the metro with any given storm. Snowfall totals typically vary over just a few miles...and sometimes heavier snow bands can be just a few miles wide. Secondly, a snowfall range indicates the inherent uncertainty and limitations to the precision of the current state of the models and snowfall forecasts. No model or forecaster has the ability to pinpoint snowfall totals days in advance with every storm.

A forecaster might get lucky every so often a few days ahead of an incoming storm, but eventually will lead the public astray and damage the credibility of our profession by implying more accuracy than the science allows. Plain and simple nobody is that good all the time, in spite of what they may be selling you.

So enjoy the snow babble leading up to winter storms...but know that while I will do my best to characterize incoming system with some useful information days in advance... my 'inches forecast' will usually come about 24 hours before the snow flies.

Canada snow cover favors cold ahead

Most of Canada is now snow covered. In fact there's a good 4 inch to 8 inch base just north of Minnesota in southern Ontario and Manitoba these days.

The extensive snow cover and longer nights mean incoming air masses from Canada pack more cold potential. The GFS and Euro hint at some very cold air the next two weeks with temps mostly in the teens by Saturday even in the Twin Cities.

Enjoy the warm up today and keep an eye out for the possibility of snow Thursday night!