Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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986 FXUS63 KLMK 060536 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 136 AM EDT Mon May 6 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Waves of showers and thunderstorms are expected today. * Potential for multiple rounds of strong to severe storms next Tuesday through Thursday. Although confidence in timing remains low, all severe hazards will be possible. * Localized flooding potential will exist where repeated rounds of heavy rainfall occur next week. && .UPDATE... Issued at 830 PM EDT Sun May 5 2024 Skies were partly cloudy across the region this evening with temperatures in the the lower 70s. Regional radars show an arcing line of convection from Paducah southeast to just south of Nashville, TN. This activity has been steadily moving northward through western TN this evening. The convection has shown a slight decrease in intensity over the last half hour with CG lightning rates continuing to diminish. Airmass out ahead of the front is still slightly unstable, but with the onset of nocturnal cooling, continued boundary layer stabilization is likely to take place leading to this convection to become more elevated with time. Nonetheless, activity is forecast by the high resolution models to continue to hold together while moving northward overnight resulting in most locations seeing some rainfall overnight. Overall character of the convection overnight looks to be more showery in nature with some embedded thunder here and there. Current forecast has this well handled at this time. Updated products have been sent. && .SHORT TERM /THROUGH TUESDAY/... Issued at 305 PM EDT Sun May 5 2024 This afternoon... The cold front will continue to push through the region. Along and ahead of the boundary, showers and storms have developed due to moisture convergence and instability growth. With sunset, these showers and storms will dissipate. Heavy rain, gusty winds, and lightning are the main threats with stronger pulse storms. Tonight and Monday... A mid-level shortwave trough will move over the Ohio Valley bringing some additional moisture, cyclonic vorticity advection, and a weak LLJ. These conditions will allow for widespread showers and embedded storms to move into the region from southwest to northeast. Given that these storms will occur in the overnight hours and have quite limited instability, there will be little to no severe weather threat tonight. Low temperatures will be similar to the previous night in the low-mid 60s. Showers and storms will continue through Monday. Instability will grow into the afternoon hours, however, values will remain mostly marginal given weak mid-level lapse rates. Very little shear, 1.6- 1.8 inch PWATs, and DCAPE values around 600-800 J/kg will lead to a pulse thunderstorm environment where strong wind gusts are possible with a water-loaded downburst. Given high PWATs and high low-mid level relative humidity, efficient rain production will lead to around 0.75 - 1.25 inches of rainfall through Monday afternoon. Some localized areas that see strong storms or a downburst may see higher QPF. Main threats with strong storms will be gusty winds, heavy rain, and lightning. Winds will be light and veering from the northeast to the southwest through the day. High temperatures will be in the upper 70s and reaching 80 in southern Kentucky and the metro areas. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Issued at 305 PM EDT Sun May 5 2024 Monday Night - Thursday... Main Message/Broad Overview... Active mid week timeframe shaping up as several waves eject out over our region from a broad western CONUS trough. Expecting to have periods of moderate to strong instability coupled with sufficient deep layer shear to support organized convection, including potential for some supercells. As a result, all severe modes will be in play at times, along with a potential flooding threat that could develop later in the mid week time frame, especially with repeated rounds of heavy rain. Damaging winds and large hail are expected to be the most common threat throughout, but again, all severe modes could come into play at times. Current focus is on three main waves. The first would be mid to late morning Tuesday into early afternoon mainly across the northern half of the CWA. Additional convective development is then expected later Tuesday evening into Tuesday night, mainly along and south of the Ohio River. The third wave would then be expect Wednesday evening into Wednesday night. Wave 1 Late Tuesday Morning/Early Tuesday Afternoon... A warm front will lift north of our area Monday night, with scattered showers and storms possible in the warm advection regime over our area. Forecast soundings would suggest this convection will be elevated in nature, with perhaps some hail with the strongest cells. Overall, severe threat would be quite low outside of an isolated hail instance, and most of that is dependent on mid level lapse rates steepening toward dawn. By sunrise Tuesday, upstream convection ahead of a cold front extending from a strong northern Plains surface low will be poised to enter our western CWA. Will be interesting to see how this plays out as the ongoing convection could outrun the best shear profile, especially if it gets a good lower level cold pool going. Another plausible scenario would be an ongoing severe weather threat as a line of showers and storms enters the CWA amid an increasingly favorable vertical shear profile beneath the exit region of strong mid/upper level jetting and a modest low level jet. Main threat would be damaging winds along with a hail and tornado threat, mainly across the northern half of our CWA. Another wave of severe storms could redevelop across our region later Tuesday night as the cold front impinges upon the area. Low confidence in exactly how this plays out as previous convection could play a factor. Nevertheless sufficient instability, sufficient deep layer shear, and an approaching cold front all suggest that severe weather would be possible. Certain models develop convection across our area for much of the nigh, so something to watch. A final, and probably the most concerning, round of severe weather then looks to be on for later Wednesday evening into Wednesday night. The main shortwave energy begins to eject out into the upper Midwest on Wednesday night with an associated surface low moving from the mid Mississippi River Valley to the Wabash River Valley. Strong instability on the order of 2500-3000+ J/KG (even on GFS soundings) will likely build during the day, and then be available (at least MUCAPE values above a slight near-surface inversion) as upstream convection builds and then moves through our region. The 05/00z run of the C-Shield model depicts a strong linear feature diving through the CWA that would likely carry a widespread damaging wind threat, large hail, some embedded tornadoes possible as well. Forecast soundings are ominous as they show big CAPE profiles in the presence of strong deep layer shear (both speed and direction) yielding curved hodographs (Effective SRH 300+ M2/S2). Supercell structures could easily accompany any linear feature, either embedded or more discrete. Depending on how many waves of convection materialize before this, we could see a Flash Flooding threat evolve by this time as well. Alternate scenario offered by the 05/12z ECMWF would suggest convection will continue across our southern CWA into Wednesday, and continually be convectively reinforced. This would limit the northward progression of the warm front, and shut down much of our severe chances across the northern half of the CWA for Wednesday night into Thursday AM. Instead, severe and flood threat would continue across our south CWA into TN. Meanwhile, the best forcing and triple point would be across central IN where more severe weather would develop. This bi-modal solution has happened in the past with southern convection robbing our region, and meanwhile a secondary and likely tornadic event unfolds to our north. This secondary solution will continue to hurt confidence a bit in exactly how this all plays out, at least for this forecast cycle. Overall, still a lot that has to happen between now and then, but concern is growing for what could be a significant event late Wednesday/early Thursday if some of the current data verifies. Stay up to date of the latest forecasts. Thursday - Sunday... Confidence lowers significantly in the late week/weekend time frame as a messy upper pattern likely swings a couple more disturbances through our area. Overall, temps be cooler in the 60s/70s with best chances for a shower or storm on Friday and Saturday night/Sunday. Quite a few ensemble members point to Saturday being one of the `coolest` days we`ve had in a while as highs struggle to climb into the upper 60s and overnight lows fall into the 40s. && .AVIATION /06Z TAFS THROUGH 12Z TUESDAY/... Issued at 134 AM EDT Mon May 6 2024 A band of showers and embedded thunderstorms is moving from SW to NE across the region at this hour. This area of rain will approach SDF/HNB/LEX/RGA over the next 1-3 hours, with the precipitation expected to be heavier at SDF and HNB, potentially resulting in temporary MVFR/IFR visibilities. While the band is expected to weaken as it moves northeast, amendments may be needed to add thunder mention if the weakening trend is slower than expected. Later this morning, an area of MVFR stratus is expected to move across the region from the west. Model guidance has been struggling with its timing as well as how low ceilings get within the area of stratus, so forecast confidence remains low. Later today, several waves of showers and embedded thunderstorms are expected to move across the region. Timing of each individual wave will likely have to be handled by short-fuse amendments, with reduced ceilings and visibilities likely in the heaviest showers/storms. Outside of showers and storms, winds should gradually increase out of the S/SW late this morning and through the afternoon. Toward the end of the forecast period, a return to VFR conditions is favored, though low stratus may try to linger tonight at SDF/LEX/RGA. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...MJ SHORT TERM...SRM LONG TERM...BJS AVIATION...CSG