Sunrise 5:34 AM   Sunset 7:55 PM Moonrise 3:23 PM   Moonset 3:04 AM

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FXUS63 KLMK 181927 AFDLMK

Area Forecast Discussion National Weather Service Louisville KY 327 PM EDT Sat May 18 2024

KEY MESSAGES

* Scattered showers and a few thunderstorms across southern Kentucky through early evening.

* Dry weather arrives Sunday with unseasonably warm temperatures Monday and Tuesday.

* Unsettled weather returns by Wednesday, with rounds of showers and thunderstorms possible through the end of the week. Severe storm potential remains uncertain, with somewhat higher confidence in the potential for localized flooding.

SHORT TERM /THROUGH SUNDAY/
Issued at 326 PM EDT Sat May 18 2024

Low-level air mass remains quite muggy today even in the face of light E-NE flow, and the extensive sct-bkn Cu field over the Ohio Valley appears thickest from Louisville over toward Lexington. Upper low has nearly closed off over western Tennessee, and continues on a due eastward trajectory. Even with the moist air mass, the deeper moisture is not as plentiful as it was Friday, with PWAT values down to about 1.3 inches across southern Kentucky, and more like 1 inch along/north of the I-64 corridor.

Precip chances continue a downward trend from what was previously advertised, though scattered showers and isolated thunderstorms are still in play south of the Western Kentucky and Bluegrass Parkways until about sunset. Given modest instability and weak shear, not expecting much in the way of intensity or organization, but it's worth noting that any storm that does develop will likely move in the "wrong" direction, i.e. toward the south or even southwest.

Fog is in play again overnight, given near-calm winds and temps likely crossing over the afternoon dewpoints. Not expecting a repeat of this morning's dense fog, but at least some shallow fog with modest reduction in visibility is possible.

Very warm and dry Sunday with a breaking upper ridge across the Ohio Valley. Temps look to climb well into the 80s in the afternoon.

LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/
Issued at 326 PM EDT Sat May 18 2024

Synopsis:

A mid and upper-level ridge axis will orient SW-NE from the southern Plains into the Ohio Valley Sunday into Monday. A broad area of sfc high pressure will initially extend across much of the Mississippi and Ohio Valleys on Sunday, working off to the east of the region Monday into Tuesday. During the first few days of the upcoming week, the overall pattern across North America will amplify as the synoptic trough along the west coast of the U.S. digs southward. While shortwave disturbances within a broader SW flow pattern will bring active weather to the upper Midwest and Great Lakes Monday and Tuesday, positive height anomalies and warm temperatures aloft should suppress most if not all convection that tries to develop across central KY and southern IN.

Monday night into Tuesday, western CONUS troughing is expected to eject northeastward across the central Plains and into the upper Midwest by Wednesday morning. Ahead of this trough, a Colorado Low will develop and move northeast in a similar fashion, dragging a cold front along with it as it moves east of the Great Plains.
Medium-range model guidance is relatively consistent is suggesting that this cold front will struggle to make it through the Ohio Valley on Wednesday as it loses support from the upper trough which will lift into central Ontario. The residual frontal boundary should remain in the vicinity for the second half of the week, with additional disturbances keeping things active across the Ohio and Tennessee valleys. Model agreement has improved with the 00Z/12Z ensemble guidance showing another system moving close to the region for Friday into Friday night, though confidence in details remains low at this time.

Sunday Night through Tuesday:

High pressure at the surface and warm temperatures and subsidence aloft will combine to suppress convection during the day on Monday and Tuesday. With the center of sfc high pressure fairly close to the region on Monday, winds should remain light, increasing out of the S/SW on Tuesday as the high pushes further to the east. The main weather impact during the early week period is expected to be above normal temperatures, with highs and lows expected to be 5-10 degrees above normal through Wednesday. Recent rainfall and soil saturation may help in reducing the high-end heat potential; however, Monday and Tuesday should still feature highs in the mid-to-upper 80s across much of the area.

Tuesday Night through Friday Night:

The first wave of precipitation chances is expected to arrive late Tuesday night into Wednesday morning as ongoing convection to the northwest of the region helps to advance the cold front eastward.
With showers and storms expected to reach western portions of the CWA just before sunrise Wednesday, the general depiction in model guidance suggests that storms should be weakening by the time they reach our area. A pool of higher moisture ahead of the cold front with PW values ranging from 1.4-1.7" should assist in the regeneration of showers and storms Wednesday into Wednesday night.
However, by this time, the stronger upper and lower jet forcing will be north of the Ohio Valley, reducing the overall potential for organized severe convection. With this being said, CSU Machine Learning severe probabilities and CIPS severe analogs (both of which receive GEFS inputs) both outline a 15% probability of severe weather on Wednesday. Model soundings and wind profiles would suggest that gusty winds and hail would be the main severe threats, as veered low-level winds would limit low-level shear and helicity.

Ensembles continue to diverge somewhat for Thursday into Friday, with the main differences related to how far south the cold front makes it. If the cold front sags farther south (favored by the GEFS), drier weather would be expected for the end of the upcoming week. On the other hand, the more northern EPS solutions would favor continued waves of showers and thunderstorms (with little to no severe threat thanks to weak wind shear) through at least Friday night. The wetter solutions would also lead to an elevated flooding threat for the late week period, though confidence in any one solution remains low at this time.

AVIATION /18Z TAFS THROUGH 00Z MONDAY/
Issued at 118 PM EDT Sat May 18 2024

Earlier fog has lifted into a MVFR stratus deck that continues to diminish. SDF has already gone VFR, as has HNB, while LEX/BWG will probably initialize MVFR and either lift to VFR or scatter out by 20Z. There's a small chance for afternoon showers or thunderstorms in our south and east, so will include VCSH til 00Z at BWG and RGA.

Fog potential tonight is another question, as the models aren't hitting it at all, but it looks like temps will cross over current dewpoints. For now will include a TEMPO for MVFR vis in LEX, and IFR at BWG and HNB on Sunday morning. A slightly drier low-level air mass should be a mitigating factor, so would not expect it to sock in quite like what we saw this morning.

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

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