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Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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615 FXUS63 KJKL 230901 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 501 AM EDT Mon Sep 23 2024 .KEY MESSAGES... - A potential for showers and thunderstorms will persist through much of this week. - After high temperatures well into the 80s to near 90 earlier today, readings will trend downward through the week. && .SHORT TERM...(Today through Tuesday) Issued at 419 AM EDT MON SEP 23 2024 Aloft, flattened ridge continues to be broken down by shortwave energy associated with a trough moving out of the central Plains and into the Ohio Valley. This trough manages to make it into eastern portions of the Commonwealth by the end of the short term, just as another, deeper system drops southward into the Missouri Valley. At the surface, a nearly stationary frontal zone is positioned along the Ohio River just to our northwest. This feature, combined with passing disturbances aloft, will provide a focus for sporadic episodes of showers and thunderstorms across eastern Kentucky through the period. Sensible weather features a generally unsettled short term, with periods of showers and thunderstorms impacting different portions of eastern Kentucky, as well as the region, at times through the short term. H850 temps between 16-17C combined with the increased cloud cover and higher potential in PoPs will help keep afternoon highs in the upper 70s to mid 80s through the period, or about 5-10 degrees lower than the recent upper 80s to lower 90s we have been experiencing. The Storm Prediction Center has our area in a Marginal risk for severe weather today and again on Tuesday. In addition, the Weather Prediction center has our area in a Marginal risk for excessive rainfall. Overall, the risk for strong to severe storms will be conditional, as is often the case it seems. Today, we will see marginal instability, on the order of 500-1000 J/kg of MLCAPE and bulk shear is lacking, generally less than 25kt, though it does increase to around 30 kts tonight. Mid-level lapse rates are modest, climbing to around 6 C/km. However, there is a relative lack of triggers through much of the day as the better, more organized shortwave energy holds off until later tonight and Tuesday. Thus we will be dependent on the surface front to our northwest and differential heating to help initiate convection today. This suggest convection will be more isolated to scattered today, and less organized. But there are enough ingredients in place that a strong storm or two could not be ruled out. Tuesday appears more favorable for strong to severe storms with MLCAPEs on the order of 1000-2000 J/kg, and bulk shear of 40-50 kts. However, mid-level lapse rates are weaker. In addition, it is likely that there will be more cloud cover across the region on Tuesday. Consequently, severe weather potential will be increase with more sunshine...or heating. Shortwave energy appears more organized on Tuesday. Thus convection, as well as the potential for strong to severe storms appears more likely on Tuesday. Storm motions are decent through the period, 10-15 kts today, increasing to around 30 kts or greater by Tuesday. Freezing levels are generally less than 13 kft and PWATS max out at around the 75th percentile, climatologically. Thus conditions are not ideal for widespread flooding issues. Everything considered, feel that any hydro issues will be localized, and more dependent on how organized convection becomes and the potential of training and/or the back building of storms over specific locations. .LONG TERM...(Tuesday night through Sunday) Issued at 501 AM EDT MON SEP 23 2024 There are two large scale features which will interact with each other and dominate our weather during the long term period. One of these is a high amplitude upper trough which will start the period over the Great Lakes and Mississippi Valley. The other is a tropical system which will evolve from the area of unsettled weather currently off the east coasts of Honduras and Nicaragua. The upper level trough will be drawing on deep mid/upper level moisture being pulled north from a fetch along the western Gulf Coast. Precip is expected to be ongoing over at least part of the area at the start of the period. Models indicate, to varying extents, a dry slot wrapping around the trough. Because of this feature, a POP gradient is placed across the JKL forecast area Tuesday night and Wednesday, with the highest POP in southeast KY and the lowest in the Bluegrass region. Confidence in the exact placement of features at that time range is not high, so the POP pattern represents the best estimate based on the most recent model runs. The dry slot degrades on Wednesday and Wednesday night and a more generalized, decreasing POP blankets the area. This happens as the upper trough develops a pronounced closed upper low to our west. By the time we get to Thursday, models suggest the tropical system will be a hurricane moving north through the Gulf of Mexico, with its moisture starting to get drawn north around the extratropical upper low to our west. Both the ECMWF and GFS have the upper low capturing the tropical system and track its remnants north through KY on Friday. Have used an increasing POP on Thursday night as it approaches, with a peak of 60-70% on Friday. This is influenced by the latest available model runs of the GFS and ECMWF, and is higher than the latest available national blend of models. Once the weakening tropical system departs to the northwest, models show another dry slot wrapping around the upper low and reaching us Friday night and Saturday. This results in a relative minimum in the POP. By the time Sunday rolls around, model solutions begin to diverge more. The GFS weakens the upper low and tracks it east over KY, while the ECMWF weakens it but lets it meander further west. Either way, the dry slot influence would be waning and the POP creeps a bit higher once again. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) ISSUED AT 157 AM EDT MON SEP 23 2024 Surface cold frontal zone is draped along the Ohio River just to our northwest. Subtle disturbances continue to track through the Ohio Valley, producing additional shower and thunderstorm activity, some of which is redeveloping just upstream of our forecast area at TAF issuance time. The strongest of this activity will impact mainly KSYM, KSME, and possibly KLOZ. Otherwise, some light showers are also moving through the area. Thus far activity could be described as sporadic and diverse in nature, making it more of a forecast challenge with respect to predominant weather groups at any given location. Overall this leads to a lower than normal confidence level with respect to flight categories at any given period of time. In general, feel VFR conditions are a reasonable bet, but there will be drops in flight conditions, particularly VSBYS where showers and thunderstorms do pass. Model guidance, and especially higher resolution short term convective allowing models show an overall downward trend in activity through the remainder of the overnight. Thereafter, expect convection may redevelop and overspread eastern Kentucky from southwest to northeast by around mid-afternoon. Once this activity dies down, fog will likely redevelop late in the period. Winds will be light and variable through the period, except in the vicinity of any thunderstorms where winds could become gusty. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...HAL LONG TERM...RAY AVIATION...CMC/GREIF/RAY