071
FXUS63 KLMK 171946
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
346 PM EDT Fri May 17 2024

.KEY MESSAGES...

*   Widespread showers and scattered storms today and Saturday, with
    locally heavy downpours possible.

*   Drier Sunday with hot temperatures Monday and Tuesday.

*   Showers and storms return Tuesday with increasing potential of
    strong to severe storms on Wednesday.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 344 PM EDT Fri May 17 2024

Rain shield across the lower Ohio Valley is diminishing in coverage
as an upper impulse departs, leaving behind weak lapse rates and not
much in the way of lifting mechanisms. Main upper trof still hanging
back across the Red River Valley, and expected to move slowly
eastward into the Tennessee Valley by Saturday evening.

As we lose lifting and then heating late this afternoon and this
evening, expect the diminishing trend in precip to continue. Thunder
chances will remain low, but not diminish as quickly especially if
we get breaks in the clouds. The overall theme will be intermittent
rain eventually tapering off completely.

Humid and stagnant air mass overnight will be favorable for fog,
though enough cloud cover is expected to persist to mitigate the fog
potential. Still could easily have a stratus build-down, so we`ll
mention fog but will not go as far as dense fog. Any dense fog
should remain confined to the most sheltered valleys and typical fog-
prone locations.

Saturday will be on the muggy side with seasonable temperatures.
Confidence in the precip forecast is much lower. Recent trend is to
suppress most of the moisture feed in the Tennessee Valley as any
southerly flow is fairly weak. However upper trofiness over a humid
and relatively uncapped air mass will yield at least isolated
showers over southern Indiana, with better chances along and south
of the Parkways in Kentucky. Poor lapse rates will limit rainfall
intensity and storm severity, though we can`t rule out a rumble of
thunder.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 344 PM EDT Fri May 17 2024

Saturday Night through Sunday Night...

The upper low which is bringing the unsettled weather to the region
today and tomorrow will begin to pull out of the region Saturday
night. Any showers and thunderstorms which are ongoing Saturday
evening would be expected to dissipate with the loss of daytime
heating, with most of the overnight hours expected to be dry. There
is an enhanced potential for fog across the region late Saturday
night into Sunday morning given the expected combination of moist
soils, light winds, and clearing skies.

Sunday should be the first in a stretch of two or three relatively
quiet days as mid- and upper-level ridging builds from the southern
Plains northeastward into the Ohio Valley. A diffuse area of sfc
high pressure will move across the region, resulting in weak winds
speeds. Low level moisture will remain in place, with dewpoints
Sunday afternoon still in the low-to-mid 60s. However, warmer
temperatures aloft, especially in the 850-700 mb layer, and the lack
of any large-scale forcing should curtail precipitation chances.
Warm, muggy conditions should continue into Sunday night, with
another possibility for areas of fog Monday morning, depending on
how much mixing and drying there is during the day on Sunday.

Monday through Tuesday...

Warm and humid conditions are expected to continue into the first
few days of next week as upper ridging builds downstream of an
amplifying trough over the western CONUS. There is elevated
confidence in dry weather Monday and Tuesday, because while there
will be some instability present and steep low-level lapse rates,
any triggering mechanism in the form of a sfc cold front or upper
level forcing should remain well to the north and west of the region.

The main focus during this time period will be on above normal
temperatures, with highs progressively warming through Tuesday as SW
flow increases ahead of an incoming trough. NBM probabilities of
highs 90 degrees or above range from 20-30% along and west of I-65
on Monday, increasing to 30-50% on Tuesday. Recent rainfall and
saturated soils will limit the top end potential for temperatures,
so expect most locations to remain in the mid-to-upper 80s.

Tuesday Night through Thursday Night...

The next period of unsettled weather looks to arrive Tuesday night
into Wednesday as an upper trough and attendant sfc cold front cuts
into the ridge in place over the eastern CONUS. Increasing moisture
and forcing ahead of this system, along with falling mid- and upper-
level heights will re-introduce the potential for showers and
thunderstorms across the region. While machine learning and analog
severe prediction tools show elevated potential for strong to severe
storms Wednesday into Thursday, it continues to look like the best
combination of instability and shear should remain west and north of
the region at this time. Also, while susceptibility to flooding
should decrease somewhat given expected dry weather Sunday through
Tuesday, heavy rainfall could once again lead to localized flooding
issues during this time period.

Heading into the end of next week, model guidance diverges and
forecast confidence decreases. In general, ensembles suggest a
return to a more zonal pattern, though some of this is due to the
averaging of differing solutions.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 121 PM EDT Fri May 17 2024

Widespread showers continue into the afternoon as we have a weak
upper impulse moving ENE through the Ohio Valley, and a moist air
mass in place. Thunder is a non-zero but very low probability given
very weak mid-level lapse rates. Precip not heavy enough for any
restrictions to vis, but we could yet have some TEMPO IFR cigs,
especially at SDF and LEX.

Precip should come to an end this evening, with a favorable setup
taking hold for fog/stratus. Winds will be light and the ground
fairly wet in some places, and even though we will maintain decent
cloud cover, model guidance is pointing to some form of build-down.
Look for a fairly extended period between 07-14Z with MVFR vis/cig
below 2000 feet.

Recovery to VFR will happen mid/late morning on Sat, with light E-SE
winds. Isolated to scattered showers and a few storms will be
possible, but probabilities remain too low to mention in the TAFs.

&&

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

&&

$$

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