Models Differ From Oct 2-9

Okay. My last forecast based on the GFS and ECMWF was a bust. But, even the NWS office in Louisville could not get those high temperatures right for the week either. The dry ground made it difficult even one day in advance much less several days out.

Now, for the upcoming forecast period. Instead of the GFS and the ECMWF agreeing like this past week, there are significant differences by the time we get into the beginning of the work week.

Both models agree that after a balmy Thursday, temperatures will be quite cool come Friday night through Sunday morning. The GFS is actually colder for its highs on Saturday than the ECMWF.

Granted, cold air advection can make a mess of a computer model's idea of what surface temperatures will be like. Cyclonic flow will advect colder air into the region on the heels of stiff northwest winds by Friday night as temperatures will fall throughout the day on Friday.

Saturday looks very cool, cold compared to the 80's. GFS shows 52 degrees for Louisville while the ECMWF shows 56. I think those numbers sound reasonable as we will not be under the influence of high pressure but continued cyclonic flow around low pressure. That means more clouds than sun during the heat of the afternoon, putting a lid on rising temperatures.

Saturday night into Sunday morning raises a question mark. Will the winds relax enough and skies clear enough for patchy frost formation?

Generally, under cyclonic flow, there is normally a measure of some wind and some clouds. However, I have seen when winds relax and skies clear a couple of hours before sunrise. And I think that will happen in this instance for many locations.

Look for several areas with readings in the mid and upper 30's. With calm conditions, expect patchy frost confined mainly to rooftops, windshields, and iron rails. Some tender vegetation may be impacted, but this should not be a killing frost ending the growing season for many of us. But, I would not be surprised in valley areas or higher elevations of the Bluegrass and eastern KY that widespread frost may potentially damage plants.

If clearing should occur, expect the NWS offices to put out Frost advisories for areas generally east of I-65 for the Sunday morning time frame.

By the beginning of next week, the models differ on how things will progress for the rest of the time period through Thursday.

The Euro shows a reinforcing shot of cooler air arriving by early next week while the GFS maintains that temperatures will be steady and slowly rise throughout the forecast period.

According to the Euro, Louisville's temperatures would slowly recover from highs in the lower 60's on Monday to possibly mid 70's by next Thursday while the GFS has upper 60's rising to the mid 70's during the same time. I am siding with the ECMWF.

MS