Since my last post on October 10th “Interesting pattern last two weeks of October” the jet stream has indeed been as progressive as predicted with a number of recent storms. The next storm on the horizon should bring beneficial rainfall to much of the Mid-South for much of next week.
The 10/10 post centered on the evolution of the storm system that is now approaching the Pacific Northwest. I discussed that a zonal flow is unstable over time and will likely result in a deep trough over the Rocky Mountains. This is precisely what will happen this weekend. Southerly flow will again push temperatures in the Mid-South to near record levels in the 80s on Sunday and possibly Monday.
By Monday afternoon, the storm will be cut-off from the jet stream which will cause the system to slow down and also limit any arctic air from mixing into the system. Divergence aloft combined with a moist southerly flow should allow for numerous showers and thunderstorms over the Mid-South from Monday afternoon through late Tuesday. With such a large cold-pool aloft (1000-500 mb thickness around 5400m just to the west) there should be widely scattered showers and thunderstorms through the remainder of the workweek with temperatures in the low 60s. As the storm departs over the weekend, a ridge will build from the departing high which will make for a warm and dry start to November.
There is strong model agreement that a cut-off low will exist across the central United States next week. However, there is some variability in the GFS ensembles and among some of the other models as to exactly where the cut-off will be located. The exact placement of the low will determine whether or not the Mid-South gets appreciable rainfall or spotty amounts.
While any 336 hr forecast on any given model run is mere speculation, the Day 14 run of the 12z GFS has the first major winter storm of the season for the northern plains. Winter is not far away.