835 FXUS63 KLMK 261140 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 640 AM EST Fri Feb 26 2021 ...Updated Aviation Discussion... .Short Term...(Today and tonight) Issued at 325 AM EST Fri Feb 26 2021 Mid-level water vapor imagery shows a well-defined shortwave trough moving east over KS/OK early this morning. Just southeast of this feature, strong upper level divergence is occurring in the right- entrance region of a 160+ kt upper jet streak centered over the Upper Ohio Valley. A sfc boundary is draped from Texas eastward across the Deep South. A very moist airmass and robust isentropic lift are contributing to a band of showers and thunderstorms on the north side of the sfc boundary, from northeast TX across AR/northern MS and AL. Rain chances will increase today from south to north across central KY and southern IN, but the thunderstorms and heaviest showers will remain south of the TN border. The atmosphere remains fairly dry due to the proximity of the sfc high, with PW values around 0.4 inches. The upper wave currently over OK is forecast to cross the forecast area today, and low-level ridging quickly moves off to the east. 850 mb winds veer southerly today and increase throughout the day. Developing southerly moisture return will allow PW values to climb to 0.8 inches. Light to moderate rain is expected to spread into southern KY during the mid to late morning hours, with rain chances continuing to spread north across the rest of central KY and southern IN in the afternoon. Rain chances will generally be more scattered along and north of the Ohio River, with the highest rain chances further south and east. Daytime rainfall could reach a tenth of an inch near the WK/BG Parkways, with up to a quarter inch south of the Bluegrass Parkway. Highs today will be in the upper 40s to mid 50s. More focused, stronger isentropic lift arrives in southern KY late tonight into early Saturday on the nose of a 40 kt southwesterly LLJ. Strong low-level moisture transport occurs from southwest to northeast across Middle TN this evening, nosing into south-central KY late tonight. 1.2 to 1.3 inch PW values nose into south-central KY between 06-12z Sat. Heavier rain totaling 0.50-1.00 inches in a 12-hr period through 12z Sat looks possible south of a line from Scottsville to Columbia (highest QPF in the Lake Cumberland region). Lows tonight are expected to range through the 40s. .Long Term...(Saturday through Thursday) Issued at 335 AM EST Fri Feb 26 2021 ...Significant Heavy Rain Possible Over the Weekend... Saturday Weak area of high pressure builds in over Kentucky during the day Saturday. This will bring a brief "lull" in the heavy rain. There will be a few lingering rain showers across the southeastern portion of the county warning area along the Lake Cumberland region with precipitation amounts a tenth of an inch or less. Saturday night - Sunday night Ingredients remain in place for heavy rains for the second half of the weekend. Strong southwesterly LLJ of 50-60kts lifts in across central KY/southern Indiana under the right entrance region of the upper level jet. Model trends continue to push the heavier band of rain more northward along the Ohio River across southern Indiana and northern Kentucky Saturday night into Sunday morning. PWAT values will range from 1.25 to almost 1.50 across central KY into southern Indiana. This period looks to be where we experience our highest rainfall rates with a half an inch across southern KY to near 2 inches along the Ohio River for northern KY/southern IN by Sunday morning. While a rumble of thunder can't be ruled out, instability will be weak and the atmosphere remains very saturated. During the day Sunday, a cold front will slowly start to push the heavy rain band off to the south-southeast south of the parkways into the Lake Cumberland region. An additional three quarters of an inch to just over an inch is possible across southern KY. Rain showers will taper off Sunday night into Monday morning. Total rainfall will range from 1.5 inch in southern Indiana with around 2.5 to 2 inches across central KY and up to 3+ inches across our southeastern corner of our CWA. Monday - Thursday Models continue to differ on how to handle things going into next week. Other than some lingering light rain in the Lake Cumberland region early Monday morning, Monday and Monday night should be dry with high pressure building in from the northwest. Beyond Monday the models really diverge as the GFS wants to keep us dry for most of the week with the exception of a system coming in Thursday night into Friday. On the other side, the EURO has a system coming in Wednesday into Thursday but dry for the end of the week and into the weekend. For now, due to the uncertainty, keeping chance of precipitation in the forecast Tuesday and Thursday until we see a little more agreement in the model trends. Temperatures trend to be near or even slightly above normal in the low to mid 50s through the week for highs and mid 30s for lows with the exception of Tuesday morning where lows could be in the upper 20s to low 30s. && .Aviation...(12Z TAF Issuance) Issued at 640 AM EST Fri Feb 26 2021 VFR conditions likely to continue through the rest of the morning. Ceilings expected to drop to low MVFR/IFR from south to north this afternoon and evening. Light rain will spread into southern KY, including BWG, during the mid to late morning hours. Rain is likely to reach SDF and LEX during the early afternoon hours. Sct-Bkn light showers should reach HNB by mid-afternoon, and the rain duration at HNB will be shorter. A lull in precip looks likely through the evening hours once this first wave of light rain has pushed north of the terminals. A second wave and increasing southerly low-level winds and moisture transport will bring additional showers to the region tonight (mainly after 03z). The heaviest rain tonight will be across southern and eastern KY, especially east of BWG toward SME and LOZ. Expect poor flying conditions to persist overnight due to low ceilings, and lower vsbys in rain. && .Hydrology... Issued at 422 AM EST Fri Feb 26 2021 Antecedent conditions: The first two waves will have produced light to moderate rains. The snow pack is gone and Kentucky Mesonet data shows soil moisture briefly spiked, but has since stabilized below 50 percent (below 40 percent in some areas). Soil temperatures in the top 40 inches are all well above freezing, so absorption won't be hindered by frozen ground. Total rainfall from Friday through Sunday night should range from 1.50-2.50 inches in southern Indiana and 2-2.50 inches in central Kentucky. The Lake Cumberland region in south-central KY could see 3- 4 inches. Rivers... Smaller streams have crested, and the Ohio above Louisville has begun to crest, suggesting that the water from the snowmelt continues to work its way through the system. By the time the heaviest rain arrives, it will be almost a week since the last of the snowmelt, which should work in our favor. The most likely area for any minor flooding next week should be along the lower Green and Barren rivers where levels are already up and that's where the heaviest rain is currently predicted to fall. The Salt, Rough, and Kentucky will have to be watched closely as well. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Short Term...EBW Long Term...BTN Aviation...EBW Hydrology...13/EBW