Column: Some brief chilly periods in this week's forecast, but no prolonged cold

Our next quick hit of arctic air will arrive Tuesday and last through Thursday. While it won’t be extreme cold, it will be sufficient to spray around some lake-effect snow Tuesday night and Wednesday.

Here's a model examination of timing and placement for the snow. No problems are indicated for the Tuesday commutes. With a windy start to the day, a few lingering rain showers will turn to snow showers.

Temperatures will tumble during the day, approaching the upper 20s by the dinner hour. By late in the day, the arctic air will deepen, with sparse coverage for any developing lake snow on a west-northwest flow. You can see the upstream connection with the upper Great Lakes and Lake Huron to our north.

By the predawn hours Wednesday, lake-effect snow begins to organize over the hilly terrain well to the south.

However, by 8 to 10 a.m., a disturbance will back low-level winds to a more southwest fetch, sending the band of lake snow up to the metro area. Wind speeds will also be increasing, producing some blowing snow with modest accumulations.

The band may even pay a short visit to some of the nearby Northtowns and northeastern 'burbs. The winds will begin to veer back to more west-southwest and west by mid- to late afternoon. This high-resolution model depicts the organized band to be south of the metro area by mid- to late afternoon. Gusty winds of 20-30 mph with a few stronger gusts will assure some reduced visibility wherever the band is for drivers.

If these models are accurate for timing of wind shifts, what we call the “residence time” for this lake snow band to set up over any location near the metro area will be relatively brief. This would mean lower accumulations due to the lack of duration. This is reflected in the model’s projected snow totals, which are anything but impressive.

It appears to come down to a relatively short burst of nasty driving conditions moving from south to north across the metro area and then dropping quickly back toward ski country. For pedestrians, the wind chill will be nasty, running in the low teens by afternoon with actual temperatures mainly in the mid- to upper 20s.

By Thursday, it will still be cold but much more tranquil, with some sunshine to help with the upper 20s. As far as the wintry cold goes, that will do it for awhile as a quick pattern reversion returns. This depiction of the Friday upper-air pattern in the European ensemble was posted by Michael Ventrice of IBM’s the Weather Co.:

This pattern favors a west-to-east flow from the Pacific, cutting any true arctic air off far to the north and assuring a return to above average temperatures across much of the continental United States. Following that, the European ensemble runs a train of brief warm-ups followed by brief cool downs with more of the same to follow. Looking further out into the less reliable two-week time frame, the American ensemble mean depicts a similar pattern with no lasting cold periods, as seen here by around Dec. 22-23.

As I’ve explained, probably ad nauseum, uncertainty increases with time. This progressive Pacific flow could still be shaken up in the ensembles over the next week, so nothing so far out in time can be called a high-confidence forecast. By way of a second opinion, the Climate Prediction Center also favors probabilities for above average temperatures eight to 14 days out.

Below is a NOAA graphic showing the climatology of White Christmas probabilities based on past records. On their website, you can actually point and click on particular locations and view the exact probabilities based on past records.

This past climatology doesn’t tell us much how things will work out in this particular year, based on current and future patterns in December. The quick hits of cold I’ve described could still allow for a White Christmas, especially if the timing is close to the holiday.

However, if the pattern now showing in the ensembles out to the days preceding Christmas — that's a big if — comes to fruition, I would project our probabilities for a White Christmas this year to be lower than the above climatology. I’m not saying prohibitively low chances; just lower than average.

Naturally, I will keep you updated.