Sunrise 6:27 AM   Sunset 8:53 PM Moonrise 6:18 PM   Moonset 4:05 AM

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FXUS63 KLMK 211042 AFDLMK

Area Forecast Discussion National Weather Service Louisville KY 642 AM EDT Tue May 21 2024

Updated Aviation Discussion

KEY MESSAGES

* Dry weather and above normal temperatures continue today.

* Unsettled weather returns Wednesday, with on and off chances for showers and storms through the weekend.

* Strong to severe storms possible Wednesday afternoon into Wednesday night, with an increased risk for localized flooding Thursday through Monday.

SHORT TERM /THROUGH TONIGHT/
Issued at 300 AM EDT Tue May 21 2024

Overnight satellite imagery shows a bit of mid-high level cloud cover pushing through the region this morning. Area radars were devoid of echoes and temperatures ranged from the lower 60s in the valley locations to the mid-upper 60s on the ridges. The local warm spot was down in the Bowling Green area where temperatures were in the lower 70s. For the remainder of the overnight period, no significant weather is expected.

For today, we expect a similar weather day across the region. A mid- level ridge axis will push east of thee area and the pressure gradient will tighten up a bit. Our surface winds will veer from the south-southeast to the southwest and become gusty from the late morning through the afternoon hours. We'll see another diurnally driven cumulus field develop. The latest guidance is a bit drier than in the last several runs as the models are resolving the poor mid-level lapse rates across the region. It is still is possible that a few renegade showers/storms could develop this afternoon. If so, the most probable area would be over in the Bluegrass region and the probability of coverage would be 10 percent or less. High temperatures will be in the mid-upper 80s.

For tonight, winds will diminish toward sunset. Widespread convection should be in progress across the MO Valley into the Midwest with a significant outbreak of severe weather likely over the upper Midwest. Most convective allowing guidance shows a line of showers/storms pushing across eastern MO/IL and eventually into IN/KY a few hours after midnight. This convection will initially be rooted in the surface layer, but as it moves into our region late tonight, it will become increasingly elevated and will be moving into an environment that is more hostile for sustaining it. With that said, a few showers and storms will get into our region late tonight with the best chances in areas along and west of I-65. Lows overnight will be in the upper 60s to around 70.

LONG TERM /WEDNESDAY THROUGH MONDAY/
Issued at 300 AM EDT Tue May 21 2024

Wednesday through Wednesday Night...

A vertically stacked low pressure system will be centered over the northern Great Lakes on Wednesday morning. This system will send a line of storms through the Midwest and into the Ohio River Valley.
By Wednesday morning, this line will weaken while moving through the region. The line will have outrun the best instability and dynamics, therefore, dissipating over the Ohio Valley. A moist airmass with low 60s dew points and PWATs around 1.5 inches, could lead to heavy downpours and gusty winds with stronger storms.

Guidance trends continue to suggest atmospheric recovery for convective initiation potential along the approaching cold front by Wednesday afternoon and lasting into the overnight hours.
Destabilization will bring SBCAPE values into the 1000-1500J/kg range. 40% of LREF and NBM ensembles exceed 1500J/kg. Low-level lapse rates will slowly increase, while mid-level lapse rates will be in the 7-7.5 C/km range over the northern third of the region.
90% of ensembles agree on at least 25-30kts of sufficient, but marginal deep-layer shear. Moderate moisture advection into the region will bring surface dew points into the mid 60s and PWATs around 1.75 inches. These conditions could lead to heavy downbursts/wet microbursts, damaging winds and marginal hail.

Greatest threat area is over the northwestern half of the region, which is primarily along the parkways and northwest. Storms may initiate along the Ohio River and move ENE as the front pushes into the region. Areas in the SE half of the region are forecasted to see 0.25-0.5 inches of rain, where the NW half of the region is forecasted to see 0.5-1.0 inches of rain, with locally higher amounts possible.

Thursday through Monday...

The cold front will likely stall over the Ohio Valley, and coupled with multiple shortwave systems and continued southwesterly flow, will lead to increased chances for showers and storms through Monday. Temperatures will warm each day from near normal to above normal. Dew points will also remain in the mid-upper 60s, which will lead to warm and muggy conditions through Monday.

Strong to severe storms are possible, however, this will likely be determined on a day-by-day basis to assess mesoscale evolution and recovery for convective initiation. Moisture is present through the weekend and instability recovery looks possible each day, however, shear remains weak-marginal.

Given multiple days of rain and possible training of cells, flooding and flash flooding is possible. Current QPF for this timeframe is 2.5-3.5 inches, with locally higher amounts possible.

AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
Issued at 641 AM EDT Tue May 21 2024

VFR conditions are expected through the upcoming TAF period.
Scattered to broken deck of Cu will be possible through the period with bases around FL050. Winds will pick up out of the southwest with speeds of 8-10kts and gusts of 15-21kts at times during the afternoon hours as the pressure gradient tightens up. Winds are expected to diminish toward sunset. Late in the period, a line of convection will move into the region from the west. Showers and a few storms will be possible after 22/06Z. These storms will outrun the instability gradient and weaken as they cross the region. KHNB may see some thunder out of this and will include a mention of VCTS late tonight.

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

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