Since my last post in eary August, the weather over the Mid-South has been typical of August — Boring!! However, the models are showing signs of an active pattern for much of the eastern United States over the next couple of weeks. Fall is here!
The current pattern shows a ridge/trough couplet over the western U.S. and a zonal split-flow over the eastern U.S. Hurricane Ike is approaching Texas and will be greatly involved in our weather in about a week. A cold front will approach the Mid-South over the weekend as Ike moves into southern Texas. An energetic jet streak will enable the surface low over the Great Lakes to deepen from 1004 mb to 988 mb in 24 hours on Sunday. This will allow some very chilly air to surge southward into the Great Lakes (The 0C line will dip into the U.P. of Michigan).
As yet another jet streak intensifies the trough over New England, the SE ridge will slowly bring the remnants of Ike into the central Plains and finally the Mid-South by the early-middle section of next week. What really impresses me is how much cold, arctic air is already in place over Canada. That’s a pretty mean-looking polar vortex for middle September. This type of pattern, with a deep, polar vortex directly north of a sub-tropical ridge, will result in a tight baroclinic zone with a fast zonal flow. Since this type of pattern is dynamically unstable, I would expect a couple of strong fall storms to spin up during the 10-14 day period. All three teleconnections patterns are forecast to move into phases ideal for unsettled weather in the Mid-South, although none of the indices are overwhelming.
My only concern in the long range is that the ECMWF is less bullish with the idea of a strong polar vortex over Canada. The GFS ensembles are 60-40 in favor of the vortex.