The latest run of the ECMWF model shows three distinct areas of convection ongoing as of 14:00EDT Halloween afternoon.
The convective line in eastern Arkansas would then work northeastward into central Kentucky during the late evening. The timing on the main push of weather looks to be between 20:00 and midnight for the Lexington area. This doesn't mean it won't storm before then as pre-frontal cells pop up, but the main batch should come through around that time.
Following the main squall line, there may be a second line come through overnight as the airmass driving this system plows through the state.
Ahead of this system, it's going to be very windy tomorrow during the day. A Wind Advisory is posted currently by the NWS for most of the state. The ECMWF model predicts sustained winds of 18-24 MPH! This should mean that gusts will exceed 40 at times. You should tie down trash cans, loose outdoor furniture, jack-o-lanterns, and anything else that you don't want to blow away tomorrow.
Additionally, there is still a high-end Slight Risk of severe weather posted for all of Kentucky roughly west of I-75 tomorrow. Tornado spin-ups along the squall line are a possibility. If any tornadoes do spin up, these will be the type that are very hard to detect with radar and will hit quickly. These types of tornadoes have a much smaller warning time. Therefore, it is critical that even if a Severe T-storm Warning is issued for your location tomorrow, you should still take shelter (as always) as if it were a Tornado Warning instead.
Obviously, most towns have changed trick-or-treat to Friday to protect the children in case of severe weather moving in sooner. I think this is a great call. Safety first!
Previous discussion follows:
-Shawn
Right on cue, the wild ride I talked about in my last update has arrived. We had some of the hottest weather of the year early in October, and that went straight into winter-like temps this past week with lows below freezing and highs that didn't get out of the 40s. We even saw a few snow flakes mixed in with plain rain for a brief time that did not accumulate at all but for some it was neat to see.
As we head into the final week of the month the roller coaster continues. Temps early this week will moderate back to normal with highs in the 60s. The weather actually looks to be quite pleasant, so enjoy it! By Wednesday the next weather system will start to draw closer and by Halloween it will be upon Kentucky with rain and thunderstorms likely. This is not looking like a good forecast for treat-or-treat at all according to the GFS model.
The GFS model brings the heavy part of the storm in during the evening Thursday and pushes it through during the night. It shows a 110 knot jet streak overhead so there will be some decent upper air support. RH values look to be decent for this time of year also. The real question will be how much instability can we achieve during the day Thursday?
If we get some good insolation and increase in instability we could potentially see a round of stronger storms push through. The tornado threat at this point looks low, but we will have to watch model trends over the next couple of days to see how this evolves. The Storm Prediction Center currently has areas just to our south highlighted for severe weather but they do mention that Kentucky could potentially end up being included in the outlook area in later forecasts. Also, it was looking like a flooding threat from heavy rains might occur but now that is looking less likely.
The ECMWF model is slower and brings the main push of weather through overnight Thursday into Friday morning. As a result, it shows even less instability and meager CAPE values of a few hundred joules per KG at best.
If this model verifies, the threat of severe weather would be much lower. It would be possible that some areas in central KY might possibly squeeze in some dry weather during the early evening for trick-or-treat before the rain hits.
It'll take a couple more runs before we can put a finger on the exact timing of this storm system for Kentucky. The bottom line right now is this: beautiful fall weather tomorrow will slowly degrade this week and turn into rain by Thursday. Cooler air will once again spill into Kentucky next weekend behind the cold front and we'll start the cycle all over again.
-Shawn
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