A DOUBLE SHOT OF CHILL

terryswails1
38 minutes ago
3 min read

We've been talking about the coming shot of cold air for the better part of a week. Finally, the wheels are in motion for what ultimately will be a double shot of it. The first wave arrives Wednesday and the second surge, even colder than the first, will be here just in time for Friday. This animation Tuesday night shows the initial push of cold crossing North Dakota and NW Minnesota preceded by scattered showers and storms.

At 500mb you can watch the first wave of energy carve out a deep trough over the upper Midwest which allows a secondary wave of energy and cold air to dumbbell in around it. It's a very healthy looking system for this early in September.

Friday we are in the core of it with temperature departures 17–22 degrees below normal.

At 1:00pm Friday, the GFS shows readings that are only in the low to mid 50s in my northern counties.

As early as Thursday morning, wind chills of 38-43 are widespread.

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THE PARTY IS OVER...

As each surge of cooler air comes through, it will provide the forcing necessary to create some showers, generally on the light side. The first batch is already coming through early Wednesday, and the next round is due on Thursday night. Due to the showery nature of the precipitation, rain amounts vary considerably from little to nothing, to as much as 1/2 inch in some isolated spots. I'm thinking most areas get out of it with 1/10th of an inch or less. You can see how guidance is far from consistent, showing these totals through Friday night.

The GFS

The EURO

The 3K NAM

The 12K NAM

With the air aloft getting colder and colder, (the GFS showing 850mb temperatures crashing as low as -1 C in the NW Friday morning). If you can get precipitation to fall into that environment, snowflakes can reach the ground with the traditional benchmark needed for snow of 0 degrees C. That won't be a concern for us.

However, our Canadian friends in parts of western Ontario may see over a foot of the white stuff. Even there, that's early for such a high-end event.

The cold temperatures aloft will also generate quite a few clouds the next few days, especially Wednesday and again Friday. It sure looks like Friday is going to be a very frisky day with brisk winds, plenty of stratus, and perhaps a few spotty showers or sprinkles with the core of the cold air overhead creating strong lapse rates and instability. Wednesday will be blustery as well.

As for temperatures, Wednesday's readings will hold in the mid 60s north to the low to mid 70s far south. Thursday, 65 to 70 looks good from north to south as a brief period of warm advection occurs ahead of the next push of colder air. Friday, as shown above, should be quite brisk, with mid to upper 50s possible north of I-80 and low 60s south of that.

Both Saturday and Sunday morning have the potential to be quite cold, with widespread lows in the low 40s. A few upper 30s are possible in the north if we can settle the wind and keep skies clear. However, the daytime hours should be pleasantly cool both days, with passing cumulus and highs generally in the mid to upper 60s. Those readings are more typical of early October.

Next week, warmer temperatures are anticipated, with highs pushing well into the 70s by Wednesday. Some low 80s are even possible in the south as fall makes a hasty retreat. As it stands now, moisture and forcing appears limited after Friday and rain chances look meager through most of the coming week. CPC shows this for temperatures and precipitation in the 8-14 day outlook September 10-16th. Personally, I think they are too generous with precipitation, indicating normal rainfall in this part of the Midwest.