193 FXUS63 KLMK 240712 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 312 AM EDT Wed Apr 24 2024 .KEY MESSAGES... * Lows in the middle and upper 30s tonight from southern Indiana into the northern Bluegrass region, and the typical cold spots. Patchy frost possible in these areas. * Isolated to scattered showers expected for Friday. A few rumbles of thunder also possible. Can't rule out some isolated showers for southern Indiana on Saturday either. * Weekend will feature temperatures in the 80s and breezy S winds. Wind gusts 30-35 mph possible both Saturday and Sunday. && .SHORT TERM /THROUGH TONIGHT/... Issued at 312 AM EDT Wed Apr 24 2024 High pressure over the Great Lakes will build southward into the Ohio Valley today, sending drier air into the region on NNW breezes. Despite the northerly component to the wind, the heart of the cold air mass associated with the high will stay off to our north, allowing the late April sun to still pull temperatures into the upper 60s and lower 70s for many, which is only a few degrees below normal for this time of year. A possible spoiler to the MaxT forecast, however, is the chance of more widespread morning cloudiness than is currently forecast. Clouds developed just to our north from southern Illinois to central Ohio overnight. Confidence in the evolution of these clouds is low, and if they become more widespread or long-lived than currently expected, temperatures would be suppressed. Tonight the Great Lakes high will strengthen and continue to build into the Ohio and Tennessee Valleys. Northeast breezes will bring chilly air and lower dew points into the area. Though skies will be mostly clear, we won't quite have ideal radiational cooling conditions with the center of the cold dome of high pressure remaining off to our northeast near Toronto, and a breeze of 6-9mph here. The deterministic forecast calls for lows tonight ranging from the mid 30s in southeast Indiana and the Kentucky Blue Grass to the lower 40s near the Tennessee line. HREF mean indicates a greater than 50% chance of slipping below 36 degrees by 7am in rural areas northeast of a Jasper-Bardstown-Stanford line, and a 40% chance of briefly dipping to or below the freezing mark northeast of a Salem- Paris line, especially in the usual sheltered cold spots. Near- surface dew point depressions will be on the order of 3 to 5 degrees. So, for now will just include patchy frost in the forecast, which is in general agreement with neighboring offices, and will continue to evaluate frost chances and the need for any headlines. Though widespread fog is not expected for much the same reasons as for holding off on more widespread frost, river valley fog will be a possibility by dawn, especially along the Kentucky, Licking, and Ohio. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 312 AM EDT Wed Apr 24 2024 Thursday - Friday... Sfc high pressure will be centered over Lake Erie for Thursday, with deep NW flow aloft and cool easterly flow at the sfc to support temps near climate normals or slightly cooler. Temps will be cooler to our north, with areas north of I-64 expected to only reach the mid 60s. In contrast, slightly warmer conditions will be confined to our south, with south-central Kentucky counties possibly reaching the low 70s. It's possible we could see a temperature difference greater than 10 degrees from north to south in our CWA on Thursday. While all is quiet in the Ohio Valley, to our west we will see an upper level low pressure system deepen as it pivots from southern California to the Colorado Rockies throughout Thursday. By Thursday night, the upper low and associated sfc low will be tracking into the High Plains. At the sfc, an extensive warm front will stretch from Nebraska to the Southeastern US and pushing northward towards the TN/OH Valleys. Isentropic lift will support rain chances as early as late Thursday night, but the better chances will come Friday during the daytime hours as that'll be when our better overall forcing arrives. Precip coverage will be mostly scattered for the morning hours, but should become more isolated by the afternoon hours. Certainly not a washout by any means with QPF under a quarter of an inch for the day. Model soundings still show unimpressive instability, so only expecting some isolated embedded thunder throughout the day. The overall best moisture transport and instability will be well west of our area, located with the core of the low level jet across Missouri and Illinois. By Friday night, the aforementioned LLJ will be spreading eastward, and combined with a tightening sfc pressure gradient, should see an uptick in sfc winds for the overnight with not much of a nocturnal inversion expected to keep winds aloft. Moisture axis will be greatest from eastern Arkansas/western Tennessee and stretching into central Indiana, so our precip chances will be mainly focused along and north of the Ohio River. Weekend... Warm and breezy is the main story for the weekend. As the upper low that brought rain chances for Friday weakens and tracks north of the Great Lakes, a secondary upper low will be tracking into the Plains from the southwestern US. This will keep the core of LLJ winds stuck across the mid-Mississippi/Ohio Valley due to the upper low across the Plains and a broad upper high across the East Coast. Additionally, the sfc pressure gradient will be getting squeezed between the sfc high over the East Coast and the sfc low to our west, so this will further support WAA and gusty sfc winds. With deep SSW flow, strong WAA will support temps surging into the 80s for both Saturday and Sunday. Forecast is looking drier for the weekend now, with the only chance for isolated showers being across southern IN within that persistent moisture transport axis. PoPs basically follow the Ohio River, so just about all of central Kentucky is expected to remain dry for Saturday and Sunday. The main challenge will be nailing down the wind gusts. The probability of wind gusts around 30-35 mph is high, but confidence of 40+ mph gusts is medium. Certainly could see some isolated 40+ mph gusts, but the current data does not support widespread gusts of that magnitude. Early Next Week... PoPs will be making a return to the CWA by Sunday night and Monday morning as a cold front approaches from the west. Better chances for anything severe will be well off to our west, and essentially we'll have a low CAPE high shear environment by the time the cold front and associated precip arrives Monday morning. Some elevated thunder will be possible, but soundings do not suggest any sfc-rooted convection. && .AVIATION /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 117 AM EDT Wed Apr 24 2024 Areas of light rain from a VFR ceiling associated with a nearby cold front will taper off during the pre-dawn hours as the front pushes through. An area of low stratus and patchy fog has developed from southern Illinois to central Ohio. The future of this area of fog and cloud is uncertain. Recent satellite trends show little if any southward progression of the clouds, though some new cloud development has taken place over south central Indiana in the last hour. Right now confidence is not high enough to introduce a sub-2k' ceiling into the TAFs, but will include SCT low clouds in an effort to take a tentative step in that direction, and to account for the scattered low clouds that have recently popped up between IND and SDF. Northwest breezes should stay up enough to reduce chances of fog at the 06Z TAF sites, but will be something to keep an eye on. High pressure building into the region from the Great Lakes today and tonight will otherwise provide quiet weather with NNW breezes and partly cloudy skies for the bulk of the daylight hours, and mostly clear skies with light NNE breezes tonight. There may be some river valley fog by sunrise Thursday but SDF will stay VFR. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...13 LONG TERM...CJP AVIATION...13