718 FXUS63 KLMK 301200 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 700 AM EST Fri Dec 30 2022 ...Updated Aviation Discussion... .Short Term...(Today and tonight) Issued at 305 AM EST Fri Dec 30 2022 Deep SW flow will dominate our weather today and tonight as a southern stream upper wave marches eastward across Texas, and a sfc cold front slowly makes its way from its current position extending from southern Wisconsin across western Illinois and farther SW into northwest Arkansas, to just short of the Ohio River in southeast Indiana by Saturday morning. As a result we will be unseasonably mild through the period, with rain chances increasing west of I-65 today, and overspreading all of southern Indiana and central Kentucky tonight. Precip shield for now is focused just ahead of the front, and not very efficient as the low-level jet is oriented almost parallel to the front, limiting convergence. Southern Indiana will see mainly passing showers at times through the day, until the steady rain moves in late in the afternoon. Overnight QPF will be a half to three quarters of an inch for most of the area, and with little or no CAPE to support more than a few embedded T-storms across south central Kentucky, it will be more of a soaking rain so the flooding threat is very low. Temps across the region currently range from the mid 50s to around 60 in the traditionally warmer spots, and won't change much from there through the day today. Could see a few degrees of warming from Lexington southward to Lake Cumberland, and we could see a bit of a drop over parts of southern Indiana if the rain settles in. A bit steeper drop is expected in southern Indiana with frontal passage tonight, but still looking at mid 40s there by Sat morning, solidly above normal for the end of December. Central Kentucky won't drop below the lower/mid 50s. Higher confidence exists in above normal temperatures over the next 24 hours as southerly low-level flow keeps temperatures mild across the region. With cloud cover in place overnight, expect temperatures to only fall into the upper 40s and lower 50s. On Friday, continued low-level warm advection will send readings up into the low-to-mid 60s, and occasional breaks in the overcast along and east of US 127 may allow for a few upper 60s across the Lake Cumberland region. With the front approaching from the west, southerly winds will remain in place overnight tonight into tomorrow morning between 10- 20 mph before gradually weakening Friday afternoon with the front in the vicinity. .Long Term...(Saturday through Thursday) Issued at 340 AM EST Fri Dec 30 2022 Key Messages... - Unseasonably mild through middle of next week. - Rain showers end during the day Saturday - Drying out Saturday Night into Monday morning - Strong T-storms possible Monday night into Tuesday Discussion: Saturday... Sfc cold front will work into central KY and southern IN at the start of the forecast period as an upper shortwave and associated sfc low work across the Ohio Valley and Great Lakes. Rain showers and even some embedded thunder from Friday night will continue into Saturday morning ahead of the cold front. There will still be plenty of moisture ahead of the cold front with PWATs still above an inch. Some showers could still produce brief heavy rain, especially in any embedded thunderstorms across our southern tier of counties along and south of both the Western KY and Bluegrass parkways. Rain will end from west to east during the morning into the afternoon. An additional tenth to up to a half inch is possible with the highest amounts east of the I-65 corridor. Even with the passing of the cold front, temperatures will remain fairly steady through the day in the low/mid 50s along and east of I- 65 and the low 50s/upper 40s to the west. Saturday Night - Sunday Night... Drier air works in behind the departing surface boundary Saturday night into Sunday as an area of sfc high pressure builds in over the Ohio Valley. The upper air pattern becomes more zonal giving us about a 36 to 48 hour period of dry weather. As was mentioned in the previous discussion, this will allow for soils to dry out before the next system arrives late Monday into Tuesday. Lows Sunday morning will be cooler than previous nights but still ranging 10 to 15 degrees above climatological normals in the upper 30s/low 40s. Fair weather will be in place for the end of the weekend with partly sunny skies and temperatures still mind in the mid/upper 50s to near 60 in the afternoon. Monday - Wednesday... Upper air pattern turns more amplified for the start of the week. This will feature a deep trough over the southwest US and ridging over the eastern half of the US. Sfc low will develop at the base of the trough over the central plains on Monday working northeastward into the Upper MS Valley. This will push a warm front north of the area on Monday putting us in the warm sector behind the boundary. As the trough works eastward deep southerly flow along with a very strong LLJ (60-70 kts) will pump very warm moist Gulf moisture into the Ohio Valley. PWAT values will climb to around 1.25 to 1.50" during the day on Monday as temperatures warm into the 60s with mid to upper 60s by Tuesday. Some of these values start to get with in 5 degrees of record values. A negatively tilted shortwave trough will work out of the central plains Monday night and across the region into Tuesday. This along with the strong forcing associated with the LLJ will bring increased rain chances Monday afternoon into Tuesday. There remains uncertainty in the deterministic models on the associated sfc low track and even its timing. Even with the uncertainty, there is growing confidence that a very warm spring-like airmass will be in place over the Ohio Valley. With this in mind we will continue to message the idea that strong to potentially severe storms could be possible. Model soundings show plenty of shear and a wind profile the would support some spinning storms. The question will be timing of the forcing as well as the development of any instability. The SPC in their last update from Thursday afternoon had parts of western KY southwest across the Lower Mississippi Valley for the possibility of severe storms Monday into Tuesday. I am in agreement and even with CAPE values into the low/mid hundreds, that could be enough given the shear and wind profile for strong to severe storms in this setup. The other concern will be additional rain amounts of 1.50" to 2.00" of rain on top of the rain we will receive Friday into Saturday. As mentioned above, we will have about 36 to 48 hours of drying but given the convective nature of this potential activity and the high moisture content, potential flooding would also have to be monitored with this system. Wednesday - Thursday... Given the uncertainty and timing of the Monday/Tuesday system confidence is low for this period. Lingering showers can't be ruled out Wednesday morning before clearing out Wednesday night into Thursday. Cooler air will work in dropping temperatures into the 50s on Wednesday and 40s with some potential upper 30s for highs on Thursday. && .Aviation...(12Z TAF Issuance) Issued at 655 AM EST Fri Dec 30 2022 Impacts/Confidence: - LLWS ongoing, mixing out around mid-morning - high confidence - Deteriorating ceilings and visibilities in rain tonight - medium to high confidence Low-level jetting continues to keep 2000 ft winds near 40 kt, and is expected to persist until mid to late morning. After 14-15Z we mix out, but mixing-related increase in wind gusts will be partly offset by the front edging closer. VFR conditions with mainly mid-level ceilings, but some lowering in the afternoon at HNB and BWG. Conditions start to deteriorate late afternoon/early evening as the precip shield moves in from the west. SDF will drop into MVFR during the evening, going below 2000 feet by midnight and IFR before daybreak as the rain settles in. BWG will show a similar trend/timing compared to SDF, while LEX remains VFR until midnight or a bit later, but drops quickly below 2000 feet before daybreak. Frontal position will make the difference for HNB, where we expect IFR by early evening and LIFR by midnight. Winds also go light/variable with the front, as opposed to the steady south winds at the other terminals. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Short Term...RAS Long Term...BTN Aviation...RAS