612 FXUS63 KLMK 050833 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 433 AM EDT Sun May 5 2024 .KEY MESSAGES... * Isolated showers and thunderstorms are possible today, mainly south and east of the Western KY/Bluegrass Parkways. More widespread rain chances return tonight into Monday. * 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 433 AM EDT Sun May 5 2024 With multiple ASOS/AWOS sites now reporting below 2 SM visibility, have gone ahead and added patchy fog to the forecast across the CWA until 12Z. As usual, valleys and rural areas would have the greatest chance to see fog, as well as areas which have received rain over the past 6-12 hours. Updated products will be sent shortly. && .SHORT TERM /THROUGH TONIGHT/... Issued at 335 AM EDT Sun May 5 2024 Showers and thunderstorms have rolled across southern IN and portions of western and central KY over the past 3-6 hours in association with a weakening sfc cold front. At this hour, SPC mesoanalysis places the front just east of I-65, although the front loses definition the farther south you go. The front's eastward progression has been aided by convective outflows, as influence from mid- and upper-level troughing has subsided. With instability diminishing east of I-65, storms have largely fizzled over the past hour or so, with little more than light rain showers showing up on current radar. Between now and sunrise, a stray rain shower cannot be ruled out given the front's presence and ample low-level moisture; however, would expect these showers to be few and far between. The main thing to monitor between now and sunrise is the potential development of patchy fog or low stratus given light winds and ample low-level moisture. For now, we'll keep fog mention out of the forecast, but a subsequent addition may be needed depending on obs trends. Today, the aforementioned front is expected to wash out over the Ohio Valley, leaving a NW-SE oriented low-level moisture gradient across the region. Instability will vary in a similar manner, with HREF mean SBCAPE values ranging from 1000-1500 J/kg south of the Western KY/Bluegrass Parkways to less than 500 J/kg north of the Ohio River. Accordingly, the greatest potential for regenerating showers and storms late this morning and into the afternoon is south and east of a line from Bowling Green to Frankfort. Any storms which develop should be of the garden variety, as relatively weak deep-layer shear remains over the region. Temperatures this afternoon should reach into the upper 70s and lower 80s, with conditions feeling much muggier the further south and east you go. Tonight, a mid-level shortwave disturbance will eject northeastward from the mid-Mississippi Valley into the Ohio Valley. 850 mb theta-E advection downstream of this wave should facilitate the development of another wave of showers and thunderstorms, which should begin to lift from SW-NE across the region between sunset and midnight tonight. While several hi-res models show a band of thunderstorms surging into the region on the leading edge of this area of precipitation, the storms should arrive once instability starts to decrease in the hours post-sunset. As such, even though thunder is possible given elevated instability, severe impacts are not expected at this time. && .LONG TERM /MONDAY THROUGH SATURDAY/... Issued at 335 AM EDT Sun May 5 2024 ============== Monday ============== Ongoing rain showers with perhaps some embedded storms in the rain 'shield' will continue to push through the region Monday ahead of a compact shortwave trough. Elevated amounts of deep layer moisture ahead of the trough will result in poor mid level lapse rates, keeping instability levels fairly marginal through most of the day. Model soundings do show low level lapse rates steepening some by the afternoon in response to surface heating, helping to slightly increase the instability in the atmosphere, but weak deep layer shear will limit any sort of organized convective threat. Can't rule out an isolated strong wind gusts from a water-loaded downburst, otherwise, no severe storms are expected. ============== Tuesday through Thursday ============== A negatively tilted trough swinging from the Rockies into the central Plains will transition into a deep, broad upper level low (ULL) centered over the northern Plains by midweek. With weak/subtle upper level ridging stretching from the Mid-Atlantic into the Southeastern U.S., upper level flow over our region will shift to a more active southwesterly direction. This will result in multiple waves rotating around the base of the northern Plains ULL that will likely impact our region, before portions of the ULL get swept up in a trough by late Wednesday into Thursday. Severe weather parameters ahead of some of these waves warrant concern. By Tuesday evening, model soundings generally exhibit moderate amounts of instability in a strongly sheared environment supportive of organized convection. All severe weather hazards (tornadoes, hail, damaging straight line winds) would be possible. Localized flooding issues could also arise depending on QPF totals toward the end of the week. Unsurprisingly, models have some minor differences in the timing and evolution of these waves, but the best chances for severe storms will likely come Wednesday afternoon into Thursday AM as a surface low and cold front approach. Those living within the region will want to keep up to date with the latest forecast and make sure they have multiple ways to get warnings, especially since these severe storms could come through in the middle of the night when many are asleep. ============== Friday into the Weekend ============== Cooler air behind the cold front will likely arrive by Friday and persist into the weekend. 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 MONDAY/... Issued at 137 AM EDT Sun May 5 2024 An area of thunderstorms associated with a decaying cold front is located over SDF at this hour. These storms are expected to weaken over the next 1-2 hours, and are not expected to reach LEX/RGA. Temporary reductions in VIS and gusty winds would be expected with the thunderstorms. Later this morning, forecast confidence in ceilings decreases as model guidance tries to develop low stratus in the vicinity of the decaying cold front. The forecast uncertainty is mainly due to the fact that the depth of the low-level moisture is quite shallow, and cloud coverage may not be sufficient to produce a ceiling. Would expect ceilings to bounce around, especially between 12-18Z this morning before low-level moisture scatters out and high confidence in VFR conditions returns. This afternoon, showers and storms are expected to develop once again along what's left of the cold front, so TS potential will be determined by how far south/east the cold front pushes between now and then. Have removed TS mention at LEX/SDF for now, with higher confidence that SDF should remain thunder free this afternoon. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...CSG SHORT TERM...CSG LONG TERM...DM AVIATION...CSG