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000
FXUS63 KLMK 160545
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
145 AM EDT Tue Apr 16 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Showers and thunderstorms are likely Tuesday night through
    Wednesday night. The severe threat Tuesday night into Wednesday
    morning looks low, with the greater severe threat expected
    Wednesday late morning into the afternoon and evening.

*   Significant cool-down appears increasingly likely next weekend.

&&

.MESOSCALE...
Issued at 925 PM EDT Mon Apr 15 2024

Boundary draped across southern Indiana and into northern Kentucky,
with one cluster of storms that has repeatedly produced marginally
severe wind and hail in parts of Clark County, IN and Oldham County,
KY. Other storms that tried to get going in southern Indiana
struggled to sustain themselves, likely from being too far toward
the drier and slightly cooler side of the boundary.

Given the lack of coverage compared to our forecast, will cut back
some on POPs overnight, but with the hi-res models continuing to
show the boundary as a focus for convection, will hold on to a
slight chance roughly along the I-64 corridor. Marginal severe risk
seems reasonable given the steep lapse rates aloft, which would
allow any additional storms to produce hail even after the heat of
the day is lost.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 336 PM EDT Mon Apr 15 2024

Late this afternoon a cold front stretched from south of St Louis
through south central Indiana to south of Columbus OH. This front
will sink southward to around Interstate 64 this evening. As the
front moves into an unstable atmosphere, isolated to widely
scattered thunderstorms are expected to develop. Sounding progs show
fairly wide CAPE in the -10 to -30C hail growth zone with wet bulb
zero heights around 8k` this evening. These factors with moderate
deep layer shear, steep mid-level lapse rates, and a largely
unsaturated column suggest vigorous updrafts supportive of large
hail will be possible in the stronger storms, conditional on storms
developing. Long, straight hodographs, dry air from the mid levels,
and locally intense downpours indicate the potential for gusty winds
and splitting storms. Any storms that do fire this evening will
produce outflow boundaries that may interact with neighboring storms
and help to spur new convection. One factor that decreases
confidence somewhat is the presence of a layer of warm air aloft
around 500mb. Model progs generally keep convective coverage rather
low, so will accept NBM PoPs that are only around 30%. This agrees
well with neighbors.

The best timing for the most robust storms appears to be in the 6pm-
10pm EDT range, over southern Indiana and north central Kentucky.
Showers and storms may continue beyond that time range, but the
chances of severe storms will decrease as we get later into the
evening. The early summer feel outside this afternoon will be
present tonight as well, with lows in the lower and middle 60s.

Tomorrow any morning showers and storms will lift northward as the
surface boundary retreats in response to low pressure crossing
Nebraska. Tuesday afternoon should be dry, before the next round of
showers and storms moves in from the west (see below). Fairly
widespread mid-level clouds are expected tomorrow, but given recent
history and the fact that the region will be well within the warm
sector, will still go for highs in the lower and middle 80s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 336 PM EDT Mon Apr 15 2024

Tuesday night, a stacked low pressure system is expected to cut east
across Iowa while dragging a cold front through the Ozarks. This
will initiate a line of convection across Missouri that will work
its way eastward across the Lower Ohio Valley. The line will have
plenty of moisture in an airmass with precipitable water values just
over 1.5", but by the time the line begins to enter our western
counties (4-6z), the line would have outrun its instability. Model
soundings show deep layer shear will still be strong, but the line
will be elevated and sub-severe at that time. This line will likely
be east of our southern Indiana counties by 12z Wednesday and east
of our Kentucky counties by the early afternoon. Around this time,
the actual cold front will be nearing the western edges of the CWA.

Wednesday afternoon and evening, the front will begin to work east
across southern Indiana and central Kentucky. This is expected to
kick off a more concerning broken line of convection. Model
soundings agree that this round of precipitation will have plenty of
instability, ranging from 1,500 to 2,000 J/kg MLCAPE. Hodographs
also agree with deep layer shear, 0-6 km, around 40-50 knots with
strong low level storm relative helicity as well, so believe SPC`s
Slight risk is well placed. All severe weather types are on the
table, including severe winds, large hail, and tornadoes. Over the
next 24 hours, the CAMs will begin to capture this period and should
add more details.

Behind the cold front, upper flow becomes more zonal, and besides a
passing low pressure system to our south on Thursday night, which
will bring a chance for more rainfall Thursday night and Friday, the
rest of the week should be fairly quiet.

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 144 AM EDT Tue Apr 16 2024

Convective activity has diminished across the region at this hour,
and looking for a quiet remainder of the overnight into the rest of
the day. Looking for generally light SE winds to take hold early
this morning once remnant outflow boundaries settle down. Ceilings
will be VFR with Sct-Bkn mid and upper clouds.

By mid to late morning, look for stronger S winds to take hold in
the 10 to 15 mph range, gusting up around 20 to 25 mph at times.
Variable mid and upper cloudiness could hurt the gust potential, but
any breaks in the clouds should allow for the gustiness to increase.

Steady to occasionally gusty winds could last into later Tuesday
night early Wednesday morning, along with the arrival of some
showers and storms expected. Ceilings should stay VFR through the
first half of the night, although any shower or storm could reduce
vis below VFR thresholds.

&&

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

&&

$$

MESOSCALE...RAS
SHORT TERM...13
LONG TERM...KDW
AVIATION...BJS