OK, I know I’m changing gears from the more immediate interest in the tropics this week, and looking a long way out (one week), but I see some consistency in at least two consecutive runs of the GFS that interests me.
As Brian discusses in the video, the upper troughs and cold fronts this week will stay north of Alabama. But, by the weekend, a deeper trough may form in the western U.S., helping a strong low pressure area to develop east of the Rockies.
Weather systems are fascinating. One of the big things that comes into play here is known as “baroclinic instability”. Basically, whether or not an upper trough and its associated cold front intensify or just weaken and lift out is related to the temperature gradient along the front. There’s a fine line, and once you cross it, the low at the surface with the front pulls cold air south and pushes warm air north, strengthening the upper trough. This, in turn, strengthens the low at the surface and the front, starting a positive feedback. The system is unstable, and grows rapidly!
OK, enough of that. The low in the Rockies by next weekend may have enough temperature gradient associated with it to at least keep it together into the Ohio River Valley, instead of it going north into Canada. That would mean a cold front makes it all the way through Alabama next Sunday, bringing rain, and our first actually cold air.
If the model is right, we could see highs only in the 60s by next week (October 8), and lows near 40.
That is all, of course, if the model is right! But, I’d give it a decent chance, as cold air is building in the arctic regions and sun angles are getting lower and days are getting shorter quickly over North America.
We’ll see. Surface temps for next Sunday morning attached.
