FXUS63 KLMK 040558 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 1258 AM EST Wed Dec 4 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Freezing sprinkles possible between 3am and 9am. Confidence in this is low, and any precipitation would be very light. * Windy conditions expected Wednesday with gusts of 35-40 mph possible. * Cold wind chills in the teens Thursday. * Light winds but cold temperatures Thursday night, with the traditional cold spots dropping into the single digits. && .UPDATE... Issued at 956 PM EST Tue Dec 3 2024 Satellite imagery is starting to show the persistent low cloud cover we've had all day and evening finally eroding out of the area as it continues to slowly lift off to the northeast. This will provide a brief period of clearing and allow for temperatures to fall into the low/mid 20s shortly after midnight before the next wave of clouds associated with a strengthening LLJ and isentropic lift work in over the area in the pre-dawn hours. We will also start to see slow WAA advection both at the surface and between 900-800mb. The one thing we continue to watch is the possibility of some sprinkles that could occur just before sunrise tomorrow morning. We currently have a mention of freezing rain, but more likely freezing sprinkles in the forecast and decided to keep them in. Confidence remains low as many models outside of the NAM3K want to keep this time period dry. With a good amount of dry air at the surface and a shallow saturation level between 3000-5000ft, it is likely that most if not all of the precipitation would evaporate before reaching the sfc. Even with the low confidence, seeing that neighboring WFO's have similar mention of freezing rain/drizzle in their grids, decided to maintain consistency and not change the current forecast. The rest of the going forecast looks to be on track. && .SHORT TERM /THROUGH THIS AFTERNOON/... Issued at 326 PM EST Tue Dec 3 2024 Low clouds will continue to break up this evening, with mostly clear skies from mid-evening to shortly after midnight. This period of time after we lose the low clouds and before winds begin to increase overnight will be the window in which temperatures will fall the most, bottoming out around 20 degrees around midnight. A new area of clouds and increased SSW winds will move in during the pre-dawn hours, causing temperatures to rise 3-5 degrees between midnight and dawn. The clouds moving in before sunrise may be thick enough to produce some very light precipitation across southern Indiana and far north central Kentucky. Lift is expected to be weak, and soundings and atmospheric cross-sections are showing significant dry air beneath the cloud layer, so any precipitation would be very light. However, sounding progs suggest that any hydrometeors that do fall to the ground may be liquid. With very cold ground temperatures, these drops would freeze on contact. At this time, confidence is low in the occurrence of any wintry precipitation, and anything that does fall should be quite light...in the form of freezing sprinkles. However, the freezing sprinkles would roughly coincide with the morning rush. So, will go ahead and add them to the forecast, but will keep PoPs very low and restrict them to the region of greatest likelihood across southern Indiana and north central Kentucky north of a Leitchfield-Bardstown-New Castle line. During the day on Wednesday deepening low pressure near Lake Superior will pull a trailing cold front reaching down to the Ozarks. Between this system and a dome of high pressure slipping off the Georgia coast, a tightening pressure gradient and brisk sfc- 925mb flow beneath a low level inversion will lead to a breezy, gusty day under partly/mostly cloudy skies. Wind gusts of 35-40 mph seem like a good bet. Temperatures will warm well into the 40s, with some low 50s expected near the Tennessee line. && .LONG TERM /TONIGHT THROUGH TUESDAY/... Issued at 326 PM EST Tue Dec 3 2024 Wednesday Night - Thursday... Wednesday evening, a stout shortwave disturbance will be moving across the Great Lakes, pivoting to the east-southeast toward the northeastern US by Thursday morning. A sfc cold front associated with this upper disturbance will drop from NW to SE across the Ohio Valley Wednesday night, bringing a strong blast of cold advection in its immediate wake. As previous discussions mentioned, the moisture along and ahead of this system is fairly shallow, with the greatest saturation contained within the sfc-800 mb layer. However, lift along the sfc front should help to spark light precipitation, especially as you go farther to the north and east where there is deeper moisture. The main intrigue with this system will be the potential for wintry precip as the cold air intrudes from the northwest. Analysis of soundings depicts a classic "cold air chasing moisture" setup, with only a narrow window where temps are cold enough for snow while there is sufficient moisture depth for precipitation. The main window for a transition from rain to snow would be from around midnight north of the Ohio River to around 4 am along the TN border. If there are heavier bursts of snow, a quick dusting would be possible, primarily across the KY Bluegrass region. By sunrise Thursday, temperatures will have plummeted into the teens across southern IN and north central KY, with low 20s expected across southern KY. Cold advection will continue during the day on Thursday, suppressing diurnal warming in spite of what should be clearing skies. Persistent breezy NW winds will make temps feel like the single digits Thursday morning, with apparent temps remaining in the teens during the afternoon. Near record cold highs are likely Thursday, with highs ranging from the mid 20s across southern IN to the low 30s across southern KY. Thursday Night - Sunday... There is high confidence in gradually warming temperatures Friday through the weekend as the upper trough over the eastern half of North America ejects into the North Atlantic. High pressure will move across the region on Friday and will be centered over the southeast US during the weekend. This will return our area to a pattern favoring warmer return flow, though this return flow will be somewhat limited by split flow across the western CONUS, which will prevent amplification of the synoptic pattern until late in the weekend. This should also keep the bulk of the moisture to the south and west of the region, and dry weather is expected from Thursday through most of the weekend. By Sunday, temperatures should return to near or slightly above normal levels, with highs making it back into the 50s. Sunday Night into Early Next Week... Upper level energy from the aforementioned low over the southwest US will finally be able to eject eastward Sunday into Monday as it is expected to phase with a northern stream wave coming in from the Gulf of Alaska over the weekend. There is still only modest forecast confidence in this solution given the amount of lead time and the requisite phasing in the upper level pattern; however, it is looking increasingly likely that next week will start off mild and wet across the Ohio and Tennessee Valleys. Once the two pieces of upper energy phase, deep SW flow and enhanced moisture return is expected to approach from the lower Mississippi Valley. 3/00Z ECMWF ensemble mean PW begins to exceed the 90th percentile of model climatology by Monday morning, and strengthening low-level SW jet will promote the onset of precipitation Sunday night into Monday morning. While most ensemble members have some precipitation Sunday night into Monday, there is still considerable spread in expected precipitation amounts. ECMWF Extreme Forecast Index shift of tails shows some potential for a heavy rainfall event, and about 25% of ENS members exceed 1" 24-hr QPF next Monday. Model soundings generally show a saturated profile, limiting the potential for any instability and thunderstorms. Temperatures will continue to warm into next Monday, with highs expected to reach the upper 50s and lower 60s. && .AVIATION /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 1255 AM EST Wed Dec 4 2024 Impacts: * Marginal LLWS at HNB/SDF this morning. * Gusty winds from the SSW, especially after 15Z. Discussion: Mostly VFR conditions during this forecast period. The primary aviation impact will be wind. Southerly sfc winds will gradually increase through the early to mid-morning hours as a strengthening SW LLJ overspreads the area. This will produce brief marginal LLWS conditions mid-morning, but sfc winds will also be increasing out of the SW. SW winds are forecast to gust to 30+ kts between 15-21Z today ahead of a strong cold front. We will stay mainly dry during the daytime due to limited moisture depth. SCT showers are likely to develop late this evening and overnight as the cold front sweeps through the region. Highest confidence in prevailing SHRA is at LEX/RGA. A brief changeover to snow showers will also be possible late tonight near the end of this TAF period. && .CLIMATE... Issued at 326 PM EST Tue Dec 3 2024 ================== Near-Record Cold Max Thursday ================== Thursday 12/05/2024 Max T Fcst/Cold Max (Year) Louisville: 29/27 (1895) Bowling Green: 30/32 (2008) Lexington: 27/22 (1895) && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...BTN SHORT TERM...13 LONG TERM...CSG AVIATION...EBW CLIMATE...CSG