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FRIDAY'S FEATURE POST:
When it comes to cold, we've got double trouble here in the Midwest. One batch of modified Arctic air is on its way out but not before producing another very frisky night with lows in most spots well into the teens. In this graphic showing surface pressure anomalies, you can see the cold high that's slowly departing perched over Nebraska. You can also see a second Arctic high sprouting up near Alaska.
Short term we'll enjoy a return to southerly winds on the backside of the high and warmer temperatures, especially Saturday. Friday will still be plenty cold in the 30s but at least a good 8-10 degrees warmer than Thursday. Saturday is ripe for a nice jump in temperatures as compressional heating and brisk SW winds develop ahead of the next cold snap. I could see highs reaching the low 50s over the southern half of my area.
In this next graphic valid Saturday evening, you can see the the first high has weakened and drifted into south Texas. High number 2 is growing into a beast as it makes a push southward into Canada.
Finally, Monday morning the new Arctic high (1050mb) is into Montana and its game on for what could be record cold in some parts of the Midwest.
When I say that 1050 high mean business I'm not kidding. Below you are looking at the temperature departures for next Tuesday. Some are as low as 31 degrees below what's normal. By then a typical high in my area ranges from 44 to 48. You do the math and you come up with highs that very well could hold in the teens, especially if we can get a little dusting of snow in the ground which seems possible.
The new found cold will be a factor much of next week too. These are the 5 day departures Monday-Friday, averaging roughly 16-21 degrees below normal per day.
All the area in red has a 100 percent chance of being below freezing next Tuesday. Almost to the Gulf of Mexico!
These are the odds of temperatures of at least 20 below normal next Tuesday. 100% chances in red.
The odds of temperatures 30 below normal next Tuesday. Again, 100 percent chances in red.
These are the chances of a low temperature below 10 degrees.
We all know the colder the air, the less moisture it can sustain and the drier it will be. These are the forecast water vapor levels (PWATs). The total amount of water vapor available for precip in this air mass is 0.06"
That's bone dry as you can see in the PWAT departures from norm. 5 to 10 percent of normal!
That creates humidity levels as low as 25 percent. Get the humidifier going.
The last issue to discuss is the potential for snow as the Arctic front plows through Sunday night. At this point I don't see a real organized wave or spoke of vorticity to get anything real vigorous to develop. However, the air is so cold and the baroclinic boundary so tight that a post frontal band of snow is likely to develop. Snow ratios look high enough that 1 to perhaps 2" of snow could fall. If we get an inch of snow that really improves the chances for record cold so that needs to be watched for a couple of reasons. As it stands now. here's what the models are showing for snow Sunday night into early Monday. As you can see there's quite a range in solutions.
The 12k NAM
Plenty of time to figure out the snow situation and I would think by Friday night, Saturday at the latest I should have a good handle on of how the flakes fly. Meantime, get ready for a Saturday warm-up. Finish up those outdoor projects, raking, winterizing, Christmas lights, etc. The other shoe (a big one) drops Sunday night with the Arctic front. Roll weather... TS