Sunrise 6:43 AM   Sunset 8:44 PM Moonrise 4:13 AM   Moonset 5:05 PM

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FXUS63 KLMK 051450 AFDLMK

Area Forecast Discussion National Weather Service Louisville KY 1050 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 1050 AM EDT Sun May 5 2024

The surface cold front is just east of the western KY parkway at this time. As the front continues through the region in the afternoon, moisture convergence along the front and growing instability will allow for showers and storms to develop along and east of the boundary. Around 1200 J/kg of SBCAPE, little shear, and ample low-level lapse rates will allow for an environment conducive for pulse storms. PWATs around 1.4-1.5 inches and DCAPE around 800 J/kg would suggest a chance for some heavy rain or a downburst in stronger storms. The limiting factor to this scenario is the weak mid-level lapse rates. The current forecast remains on track.

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 HRRR 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 /12Z TAFS THROUGH 18Z MONDAY/
Issued at 636 AM EDT Sun May 5 2024

Scattered areas of IFR/LIFR stratus will make the first 3-6 hours of the current forecast very challenging, with ceilings expected to bounce between categories at most if not all forecast sites. Later this morning, there should be a gradual rise in ceilings as daytime heating helps to mix out shallow moisture. This should allow all forecast sites to return to VFR conditions by 16-18Z, with VFR conditions expected to continue through the afternoon and early evening hours. Winds will remain light today across the area, as a decaying cold front will be stretched out across the region. Showers and thunderstorms will be possible this afternoon at BWG, with slightly lower confidence in SHRA/TSRA at LEX and RGA.

Tonight, another wave of more widespread showers and a few embedded thunderstorms is expected to move across the region from SW to NE.
The heaviest showers and storms would be expected to bring reduced visibilities and ceilings; however, confidence in timing is too low to mention in the current forecast.

LMK WATCHES/WARNINGS/ADVISORIES
KY...None.
IN...None.

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