091
FXUS63 KLMK 182325
AFDLMK

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

...Updated Aviation Discussion...

.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 /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 725 PM EDT Sat May 18 2024

Diurnal Cu from this afternoon has thinned and will continue to
thin through the evening. With sunset, winds will become calm to
light. Guidance is still not catching on to much fog development,
however given persistence, fog ingredients, and meeting the cross
over threshold, have opted for some 1-3SM fog in the early morning.

Sunday will be a pleasant day with SCT diurnal Cu in the afternoon
and light northeasterly winds.

&&

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

&&

$$

SHORT TERM...RAS
LONG TERM...CSG
AVIATION...SRM