Sunrise 6:41 AM   Sunset 8:37 PM Moonrise 3:17 AM   Moonset 2:34 PM

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FXUS63 KLMK 030129 AFDLMK

Area Forecast Discussion National Weather Service Louisville KY 929 PM EDT Thu May 2 2024

KEY MESSAGES

* Widespread showers and scattered thunderstorms Friday, mainly in the afternoon and evening. Brief heavy rain and lightning.

* Probability of thunder is 15-25% in the morning, 40-50% in the afternoon.

* Rain and storm chances decrease for Saturday, but forecast confidence is still low.

UPDATE
Issued at 929 PM EDT Thu May 2 2024

Partly cloudy skies were noted across the region this evening. Mid- high level cloud cover continues to push in from the west.
Temperatures were in the upper 60s to the lower 70s across the region. Regional radars show some light returns coming northeast out of TN. Not seeing much in the way of reports of rain at the surface, likely due to the antecedent dry airmass in place. The atmosphere should continue to moisten during the remainder of the evening and showers will become more widespread from west to east overnight. Current forecast has this well handled, and only minor adjustments to the weather elements were required.

SHORT TERM /THROUGH FRIDAY/
Issued at 327 PM EDT Thu May 2 2024

========== Tonight and Friday Morning ==========

Dry weather will continue for this evening and tonight, but clouds will be on the increase as our next system approaches. A mid-level wave will eject out of the ArkLaTex region and track northeastward into the lower Ohio Valley tonight, resulting in a moisture advection axis ahead of an extensive cold front associated with a sfc low that will be over the Great Lakes. We should begin to see radar returns after midnight, but dry low levels will likely delay precip making it to the ground until after 06z. A few isolated embedded rumbles of thunder may be possible overnight, but instability will be very limited and elevated above the nocturnal inversion.

Shower activity will continue to spread eastward through the pre- dawn hours, and may peak in overall coverage between 10-15z as our PWATs maximize for the day around 1.5". PW values this high would be among the daily max for sounding climatology from BNA. Model soundings do show some limited instability in the morning hours after sunrise as well, so some embedded thunder will be possible then too. Overall though, the morning appears to be a soaking rain with an isolated thunder chance. The probability of thunder in the morning hours will be between 15-25% chance.

========== Friday Afternoon and Thunderstorm Potential ==========

By the early afternoon hours, the cold front will be approaching the I-65 corridor. With numerous to widespread showers in the morning, skycover guidance does not suggest much clearing out for the afternoon, which is good news for keeping severe potential low.
However, temps will still warm into the low to mid 70s with dewpoints in the mid 60s, leading to some sfc based instability.

According to our DESI tool, 70% of HRRR members support SBCAPE values greater than 500 J/kg tomorrow afternoon north of the Kentucky Parkways, and 40% of members above 750 J/kg. After 18z, the CAMs begin to show more a convective nature to precip along or just ahead of the front as the marginal instability is realized.
Fortunately, soundings show very weak flow through the column, so there won't be much shear for storms to work with. Regardless of the weak flow, our probability of thunder increases to 40-50% during the afternoon hours with scattered garden variety thunderstorm likely.

LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/
Issued at 327 PM EDT Thu May 2 2024

Synopsis...Quasi-stationary weather pattern is expected during the medium-range period as mid-level ridging extends roughly across the East CONUS and a couple of northern-stream, shortwave troughs swing by the western and central portions of the country. The resultant southwesterly mid-level flow will drag southern-stream, mid-level vorticity waves from the South towards the Lower Ohio Valley, promoting daily rain/storm chances this weekend into next next. A low risk of strong to severe storms cannot be ruled out during the Tuesday/Wednesday timeframe.

Model Evaluation/Confidence...Overall, forecast confidence for Saturday remains relatively low with some improvement regarding the evolution of the second northern-stream trough across the central US early next week. For Saturday, the wettest models (NAM-12 and some runs of the GFS, ECMWF, and UKMET) depict stronger, convectively- enhanced shortwave energy from earlier convection in the Deep South moving further west and north while the dry/drier model solutions represent a weaker wave quickly ejecting to the east. One thing to notice is that CAM guidance, including NAM 3km, support decreasing shower activity in the afternoon with perhaps isolated coverage. For next week, global guidance has started to converge on a similar output regarding the position of trough axis with some differences in the timing and structure of embedded shortwave energy. Given the aforementioned trend and continuing severe weather probabilities highlighted in the CSU and NCAR ML algorithms, a low risk of strong to severe weather is still on the table for Tuesday and/or Wednesday.

Fri Night - Saturday...Weak frontal boundary will slowly translate through the forecast area overnight while slowing down as it approaches south-central Kentucky in the morning hours. Uncertainty in the convective evolution further south will play a key role in the precipitation and storm chances during the day on Saturday, especially in the afternoon. Should a wetter solution materializes, mid-level shortwave forcing along the stalled frontal boundary will enhanced storm probability and coverage. Taking into account a consensus of the 12Z model data, decided to support a dry solution reflecting decreasing rain chances towards the afternoon with a 20- 30 percent chance of thunder as sufficient BL moisture and convective temperatures (amid some residual boundary interaction)
could force isolated convection. Lightning and brief heavy rainfall are the main hazards with any storm. Last but not least, there will be a renewed chance of showers and storms late in the afternoon and early evening as another frontal boundary approaches from the NW.

Sunday - Next Week...Daily rain and possibly storm chances will continue from Sunday and onwards as enough instability combines with southern-stream shortwave forcing. Best chance for strong, organized convection is still anticipated for Tuesday and Wednesday as the better dynamics and stronger mid-level winds spread over the forecast area. Based on available guidance, there is a low chance of severe weather without ruling out possible minor flooding if unsettled weather extends during several days.

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/
Issued at 705 PM EDT Thu May 2 2024

VFR conditions are expected this evening at the terminals. Cold front will approach from the west later tonight which will result in clouds increasing and cigs lowering. Will start to see some light precip at KHNB/KBWG/KSDF by 03/05-06Z, eventually reaching KLEX/KRGA by 03/12-13Z. We expect showers to occur through the morning hours with cigs dropping into the MVFR range after 03/12Z. Cigs may drop to IFR at KHNB tomorrow morning with some improvement later in the afternoon. For KSDF, will keep showers with MVFR cigs through the morning hours and will continue the VCTS mention after 03/20Z.

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

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