Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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648 FXUS63 KJKL 291125 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 725 AM EDT Mon Apr 29 2024 .KEY MESSAGES... - Dry and warm again today with clouds gradually increasing by this evening. - Showers and thunderstorms arrive from west to east tonight and linger into Tuesday. - Dry and trending warmer midweek, followed by showers and storms Friday into the weekend. && .SHORT TERM...(Today through Tuesday) Issued at 342 AM EDT MON APR 29 2024 Very mild once again this afternoon thanks to lingering high pressure and mainly clear skies, at least in the first half of the day. High clouds will filter in from west to east this afternoon, followed by overcast skies after sunset. Primary item of interest in the short term forecast is the cold front approaching tonight, bringing a weakening line of showers and storms. Upper-level jet support will be fleeting tonight, as the 60- knot 500mb jet lifts northeast over the Great Lakes and weakens. What remains is the entrance region of a 40-knot jet at 500mb. HREF and other CAMs advertise MUCAPE near 500-750 j/kg with mid-level lapse rates near 6.5C/km; marginal for a thunder risk. CAMs generally advertise a weakening trend in this line of showers and storms, perhaps with very little rain reaching the far eastern KY border toward sunrise Tuesday. POPs were generally slowed with this forecast package and reduced some to account for the anticipated weakening. WPC continues to paint our area in an Excessive Rain Outlook. Overall rainfall amounts are unimpressive through Tuesday (0.50" to 1" in the greater London and Somerset areas; up to 0.50" elsewhere). This ERO is therefore primarily driven by unseasonably high PWATs of 1.8" (via 00z HREF) which is well above the 1.55" daily maximum per Nashville sounding climatology. Given the weakening trend discussed in the preceding paragraph, we are not overly concerned about excessive rain. Lastly, in the wake of this line of showers and storms, there is an opportunity for a few isolated storms Tuesday afternoon. This appears driven by weak, lingering shortwaves in the low-and-mid levels, with perhaps a surface influence via washed-out remains of the cold front (noted in CAMS surface parameters). Confidence is low in thunderstorms occurring, but signals are present and thus POPs remain in the forecast. Notably cooler, with highs in the low-to-mid 70s in the wake of the cold front, but right near normal for late April. .LONG TERM...(Tuesday night through Sunday) Issued at 355 AM EDT MON APR 29 2024 The 29/00z model suite analysis beginning Tuesday evening shows an upper level shortwave trough across the Mid-Ohio Valley down through the Southern Appalachians. A more substantial upper low/ trough is found over much the Canadian prairie provinces as well as over northern portions of the CONUS from Washington to the Dakotas. At the surface, the decaying remnants of a cold frontal boundary will extend southwestward into Kentucky from a weak low over the Mid-Atlantic states while weak high pressure is centered over the Tennessee Valley. Further west, weak low pressure is found over the northern Plains with an associated cold front extending southward into Texas. The first decaying cold front, will decay near/over the Commonwealth on Tuesday night, with any associated shower activity tapering off. Heights will begin to rise as the upper level shortwave trough exits to the east. Thus, skies should clear for the most part, setting the stage for efficient radiative cooling; which, combined with light winds and low-level moisture from any rainfall earlier in the day, will set the stage for fairly extensive radiation fog formation through the overnight. By Wednesday, the upper level low over the northwest CONUS will begin to amplify while a counterbalancing ridge begins to rise across the Ohio Valley and Southern/Central Appalachians, reaching peak intensity late Thursday. This will funnel very warm air mass northward across the eastern Kentucky Coalfields, especially on Thursday when 850mb temperatures may exceed 17C (40-60% chance south of I-64, less than 40% north). Given deep mixing, 850 mb temperatures of this magnitude would easily support temperatures warming to near record levels in the mid and upper 80s. The amplified pattern begins to break down on Thursday night and Friday, with the ridge being shunted southeast while the western upper low tracks toward the Hudson Bay. As this occurs,a surface low reflection will develop and track from the Plains into northern Ontario and push a cold front, and renewed rain chances, into eastern Kentucky on Friday into Saturday. Little in the way of forcing will leave the surface front hanging up near/south of our forecast area this weekend. Model agreement then diverges significantly with respect to the overall pattern, though there are suggestions that a disturbance could ride along the boundary and bring rain chances on Sunday as well. In sensible terms, the first day of May will likely start off foggy for many of the valley locales before yielding to ample sunshine area-wide. Wednesday will turn quite warm with high temperatures forecast to reach the upper 70s to lower 80s. Even hotter temperatures, in the middle to upper 80s, are on tap for Thursday under bright May sunshine. A few isolated 90 degree readings cannot be ruled out, most likely in the deep valleys of the Big Sandy river basin. Shower and thunder chances return on Friday as the next cold front arrives. However, temperatures are still forecast to jump into the 80s before the deeper moisture moves in. Periodic shower and thunderstorm chances are also in the forecast heading through the weekend as that front stalls and potentially becomes the focus for additional rainfall, at times, over the weekend, though forecaster confidence in the details is low. Daily maximum temperatures are forecast to drop back into the mid 70s to lower 80s for the both weekend days. Nighttime lows should mainly range between 52 and 67 through the period, coolest Tuesday night and warmest on Thursday night. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) ISSUED AT 724 AM EDT MON APR 29 2024 Majority of the TAFs were in excellent shape this morning amid quiet weather conditions. Detail was added late in this TAF period to account for -SHRA and falling ceilings. A weakening line of showers (and perhaps thunderstorms) is expected to move from west to east late tonight. Due to the weakening trend, and continued slower/later arrival in latest high resolution guidance, confidence is low for the arrival time of -SHRA. MVFR ceilings are favored just outside of this TAF period according to the in- house blend. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...BROWN LONG TERM...GEERTSON AVIATION...BROWN