THE PENDULUM OF WEATHER....

3 minutes ago

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In five short weeks winter officially arrives. To that end, the days keep getting shorter and the suns rays less direct. We've lost a lot of daylight since July and without that energy, cold air continues to build at northern latitudes. So far, just bits and pieces of that have made it into the Midwest, but it appears around November 22nd or 23rd, we'll be in line for an air mass that packs a bigger punch.

Since the target date for the cold air arrival is still 9-10 days out, models will vary from day to day and run to run with the intensity. Additionally, phasing (the merger between the northern and southern branches of the jet) is also problematic. Models have a very difficult time portraying the success of the process, but at least have shown some consistency bringing a noteable change that brings colder air into the air pattern just before Thanksgiving.

At 500mb, the GFS shows a deep cold core cut-off low and associated trough centered over northern Illinois. It's opened the door for cold air to make a healthy push south.

The temperature departures the morning of the 23rd are substaintial over the center of the nation running 15-25 degrees below normal.

A mile up at 850mb., temperatures are shown at -16 to -17C. That's really cold, especially considering 0C. is the threshold necessary for snow.

THE PENDULUM SWINGS MIGHTILY...

Meantime, after a couple of chilly days recently, the pendulum is set to swing back the other way as another burst of mild Pacific air arrives late in the weekend. It has the potential to skyrocket highs over 60 degrees towards the end of next week. After that, it swings abruptly the other way with highs dropping over 30 degrees!

The last thing I will say is that what the GFS is showing is probably the worst case scenario for cold. I would expect to see a warmer solution, particularly if the amount of phasing shown fails to materialize, and that is on the table.

THE WEEKEND AND BEYOND...

Circling back to the weekend, it appears to be seasonally crisp with abundant sunshine. If you are up and at it early Saturday, expect the coldest temperatures of the year with readings of 20-25 degrees that should put an end to some of the hardy vegetation that has managed to survive. Eventually, the dry air should heat up sufficiently tin the afternoon allowing highs to reach the low to mid 40s. Sunday should be a bit warmer with 45 to 50 expected from north to south. After that, it's steadily up-up and away for readings next week.

One common aspect of our weather that will be missing is precipitation. Rain chances are pretty much non-existant through Thursday of next week. The national blend of models has this for rain totals through Thursday morning November 19th.

Once again I will leave you with the ensemble mean of the EURO weeklies which shows this for snowfall November 26th through December 27th, a consistent daily look on the weeklies that's been evident for nearly two weeks. I'm very curious to see how accurate the weeklies are when all is said and done around Christmas.