Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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358 FXUS63 KLMK 260754 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 354 AM EDT Sun May 26 2024 .KEY MESSAGES... * Multiple waves of strong to severe storms possible today and tonight. Widespread damaging winds are possible, and tornadoes and large hail cannot be ruled out. * Repeated heavy rainfall could result in flash flooding, especially over south-central Kentucky. * The greatest risk for severe weather and flooding will be after dark. Have multiple ways to receive warnings, and be aware of the dangers of nighttime flooding. && .SHORT TERM /THROUGH THIS AFTERNOON/... Issued at 353 AM EDT Sun May 26 2024 Multiple opportunities for severe weather over the next 24 hrs, with the impacts of each impulse dependent on the one before it. Because of that interdependence, confidence in the severe threat is limited. However, with multiple waves of storms to bring copious rainfall, confidence is increasing in a flash flood threat, especially over south-central Kentucky. The general idea remains the same with at least two, perhaps three waves of storms. First wave will be a warm advection wing, currently reflected by convection over the Ozarks, and will be pushing eastward across Kentucky during the morning hours. Look for that to arrive in south central Kentucky by mid-morning, but likely in a weakened state. Could see some rejuvenation as it makes its way into an increasingly unstable environment toward midday, which would support a damaging wind threat. Tornado threat will remain low in the early part of the day as the shear isn`t that strong yet. Perhaps the biggest question mark in the process is a MCV, which we expect to develop from the activity currently over NE Kansas, and how closely it will follow the initial wave of storms. This impulse could provide another opportunity for strong convection in the afternoon, if it isn`t moving into an already overturned atmosphere. The third impulse is the one that prompts the most confidence, and is expected to initiate convection shortly before sunset over southern Illinois. By this time low-level and deep-layer shear will be much more favorable, and the environment will be moderately unstable after a few hours of late afternoon heating. Expect this convection to grow upscale into a large squall line caprable of producing widespread damaging winds as it pushes ESE across southern Indiana and central Kentucky. A few segments could become oriented perpendicular to the shear vector, leading to mesovortex development and at least some tornado risk, but it will be limited by higher than ideal LCLs. Potential limiting factor in the wind threat is the timing, especially as the line pushes south and east after dark, with increasing chances for a low-level inversion to keep momentum from mixing down. All severe threats are still on the table. Flash flooding is an additional threat, and confidence is increasing that we will see at least a few locations that pick up excessive rainfall with a potential three separate waves of convection. Threat is the greatest across south central Kentucky, where recent heavy rains have lowered Flash Flood Guidance, and the late-night squall line will be most prone to hang up, potentially resulting in training storms. That area is now highlighted by WPC in a Moderate Risk for excessive rainfall, with the rest of Kentucky and southern Indiana in a Slight Risk. Didn`t want to slice things too fine, so we have hoisted a Flood Watch for the entire CWA, from 12Z today through 12Z Monday. The greatest threat will be with the final round of storms tonight. && .LONG TERM /TONIGHT THROUGH SATURDAY/... Issued at 353 AM EDT Sun May 26 2024 Monday through Tuesday Night... Deep low pressure is forecast to reach Lower MI by 12Z Monday, with a trailing cold front advancing through central IN and western KY. A trailing upper level shortwave trough will swing across the Ohio Valley Monday morning as the cold front moves through the region. This could touch off a few weak showers and storms early in the day, though most will see a dry start to the day in the wake of severe storms late Sunday. There is a slightly greater chance (30%) for showers and storms in the Bluegrass/Lake Cumberland regions in the afternoon. Slightly richer moisture and a bit more time for the airmass to destabilize prior to fropa results in the slightly higher rain chances. However, precip will be sparse overall. Expect a mostly cloudy start to the day, with lower clouds thinning during the second half of the day. It will be breezy with gusts of 20-30 mph. Highs will range from the mid 70s to around 80 F. Notable upper level troughing lingers over the Great Lakes and Upper Midwest through Tuesday night, keeping deeper moisture bottled up to our north. An amplifying upper level ridge builds from the Rockies to the Plains as sfc high pressure strengthens over the northern and central Plains. Largely dry weather is expected with lows in the 50s and afternoon highs in the mid 70s to near 80 F. Wednesday through Saturday... Ridging builds east across the MS and OH Valleys through late week, resulting in a stretch of pleasant weather. Highs will be in the 70s Wednesday and Thursday with comfortable humidity levels. Morning lows will generally be in the 50s, though some spots will see readings in the 40s Thursday and Friday mornings. Temperatures will warm back to around 80 degrees Friday afternoon. A highly meridional flow pattern will be in place heading into next weekend. Ridging slowly drifts to the east as a Plains low pressure system moves toward the region. Rain returns to the forecast for late Saturday or Sunday, though timing remains uncertain. && .AVIATION /06Z TAFS THROUGH 12Z MONDAY/... Issued at 131 AM EDT Sun May 26 2024 Impacts/Confidence: - High confidence in two or more waves of thunderstorms with heavy rain and gusty winds Sunday afternoon and evening, medium confidence in specific timing. - Medium to high confidence in gusty southerly winds Sunday afternoon Discussion... Sfc boundary draped near the Ohio River, with light easterly winds to the north and some moisture pooling just to the south. Front will begin to lift northward as a warm front overnight, with some concern about fog toward morning, mainly at LEX. However, with cloud cover, and the boundary layer trying to mix a bit before sunrise, not confident enough to include any vis restrictions at this time. By late morning, the first of at least two waves of showers and storms will push across the area from west to east. This convection will be in a weakening state, so impacts will be mostly limited. Did include a PROB30 for IFR vis in the heaviest precipitation. Once the first impulse moves through, winds will increase out of the south with gusts near 20 kt through the afternoon. Could see another wave of showers and storms in the mid-late afternoon, but not sure there is enough opportunity to destabilize. Either way, expect a break from roughly 21Z until 01-02Z, after which a line of gusty, possibly severe storms moves across the terminals ahead of the incoming cold front. Covered this activity with VCTS for LEX and BWG, but since it will most likely reach SDF first, did include a wind shift with gusts to 30 kt, and IFR vis with the TS/CB mention in the late evening. This will continue to be massaged in later TAF issuances. Suffice to say there will be intervals of stormy weather, but with periods of dry/benign weather and VFR conditions in between. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...Flood Watch from 8 AM EDT /7 AM CDT/ this morning through Monday morning for KYZ023>043-045>049-053>057-061>067- 070>078-081-082. IN...Flood Watch from 8 AM EDT /7 AM CDT/ this morning through Monday morning for INZ076>079-083-084-089>092. && $$ SHORT TERM...RAS LONG TERM...EBW AVIATION...RAS