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Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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054 FXUS63 KJKL 182050 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 450 PM EDT Thu Jul 18 2024 .KEY MESSAGES... - Showers and thunderstorms will impact the region at times through the middle of next week. The lowest probability of rain occurs tonight and for much of Friday. Probabilities then increase as we move into the new week. - A welcomed relief from hot temperatures is underway through the middle of next week. However, after a drop in humidity this evening and Friday, the moisture will make a comeback heading into next week. && .SHORT TERM...(This evening through Friday night) Issued at 345 PM EDT THU JUL 18 2024 19Z sfc analysis shows cooler and drier high pressure starting to build in from the northwest in the wake of a slowly departing cold front. With this pattern change the clouds are clearing from northwest to southeast as that drier, and more stable, air arrives. This is most evident in the dewpoints that currently range from the mid 50s northwest to around 70 in the far southeast. Meanwhile, mostly based on returning sunshine in the wake of the front, temperatures vary from the low 80s north to the mid and upper 70s in the southeast. At the same time, winds have turned more northerly through this part of the state and are running at less than 10 mph. The models, and their individual ensemble suites, are in excellent agreement aloft through the the short term portion of the forecast. They all depict a seemingly persistent troughing through the Great Lakes and Ohio Valley downstream of a nearly perpetual dome of high heights over the Four Corners region. This keeps eastern Kentucky in zonal, to slightly southwesterly, mid level flow through Saturday morning. Mainly weak impulses will track through the area aloft in this flow pattern even as local 5h heights tick up a bit to end the work week. Given the small model spread have gone with the NBM as the starting point for the forecast grids with little adjustment needed aside from some incorporation of the latest CAMs guidance for PoPs for thr latter portion of the period. Sensible weather features a welcomed cooler and less humid night on account of high pressure`s semi-push into the region. This ends by mid-day Friday, though, when the cold front to our south starts to work back north as a warm front - guiding our next chances of convection into this part of the state into Saturday morning. Did allow for some terrain distinction tonight, but mainly for just the northwest portion of the area that will have the best shot at being mostly clear the longest. Did also include a touch of river valley fog to account for more limited cloud cover and radiational conditions for a good portion of the CWA tonight and perhaps the northwest portion on Friday night. Otherwise, shower and thunderstorm chances creep back in Friday afternoon and will work deeper into the state from the south through that night. The main changes to the NBM starting point consisted of adding in some PoPs details from the CAMs for Friday and Friday night. Did also tweak northwest parts of area for some terrain distinctions tonight and again for a lesser amount on Friday night. .LONG TERM...(Saturday through Thursday) Issued at 450 PM EDT THU JUL 18 2024 Pattern aloft is relatively amplified, and anything but progressive across the CONUS through the extended. Wind fields are generally quite weak across North America through the period as well. A mean trough...low sets up over the Upper Midwest at the start of the extended and remains in place through the entire portion of the extended window. The trough does extend generally south-southwest into the Ark-La-Tex. A series of disturbances of varying strength track around the base of this mean trough before lifting northeast across the southeastern CONUS. At the surface, a nearly stationary frontal zone has established itself across the southeast, oriented from southwest to northeast, roughly from around Vicksburg, MS to Pittsburg, PA. This feature waffles north and south a bit as weak surface waves track along it. Each passing disturbance will tend to enhance shower and thunderstorm activity across the Tennessee and Ohio Valleys. This frontal zone will gradually dissipate, but the remnants appear to maintain enough definition to keep the threat of rain in the forecast for the entire period. Sensible weather features a stormy extended as a series of disturbances track through the region. Based on model solutions and guidance, there will likely be a diurnal flavor to convection through the period. The additional cloud cover and rainfall associated with each passing round of convection will tend to keep daytime temperatures down, slightly below our normal mid 80s. Overnight lows will tend to remain up due to lingering cloud cover and moisture. Thus diurnal ranges will not be typical and tend to be more muted with each passing day. Did tweak temps towards a slightly smaller diurnal range from the NBM initialization. More interesting will be the potential for rain. Eastern Kentucky could use some rain and this pattern may provide that much needed rainfall. Overall probabilities for heavy rainfall are low based on ensemble probabilistic data. PWATS for this type of pattern are relatively low, generally running below 2 inches through the period. Freezing levels are not that impressive either, generally around 13 kft or lower. Shear remains low through the period as well, less than 30 kts and for the bulk of the time well below that. Better moisture does appear to remain further south through the Tennessee Valley. However, with the extended time of unsettled weather, the potential for significant amounts of precipitation are quite high. Ensemble probabilistic data shows a high probability of reaching an inch or more of rain throughout the entire forecast period, basically 60 percent or higher for the entire area...and 80 percent or higher for areas along and south of a Berea to Campton to Paintsville line. The probability of a total of two inches along and south of the Hal Rogers/Highway 80 corridor is between 60 and 80 percent. Thus average rainfall totals for the extended period could be as high as an inch north of I-64, between 1-2 inches south of I-64 but north of the Hal Rogers Parkway, and around 2 inches south of the Hal Rogers. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) ISSUED AT 205 PM EDT THU JUL 18 2024 Residual shower activity has basically exited the bulk of the area. This departure is taking the MVFR/IFR CIGs out along with the PoPs. As a result, just about all terminals have turned VFR with the rest to follow shortly. Winds will be mostly out of the north to northeast yet generally light at only 3 to 7 kts into the evening. Outside of that, winds will be light and variable. Any fog tonight will likely be confined to the valleys not impacting the TAF sites. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...GREIF LONG TERM...RAY AVIATION...CMC/GREIF