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000
FXUS63 KLMK 161043
AFDLMK

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

...Updated Aviation Discussion...

.KEY MESSAGES...

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

*   Thursday night could carry another severe threat.

*   Significant cool-down appears increasingly likely this weekend.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 329 AM EDT Tue Apr 16 2024

Convective activity from earlier tonight has pretty much shut down,
although will occasionally see a few blips on radar along the warm
frontal boundary. This feature is currently draped in a WNW to ESE
orientation from roughly HNB down through LEX, and is expected to
slowly move northeastward to northern IL, central IN, and southern
OH by early to mid afternoon. Will keep some low chance pops across
our north through the morning to account. By midday, we`ll be placed
more solidly in the warm sector with steady to occasionally gusty S
winds taking hold by late morning. Overall, the gustiness may be
held a bit in check by fairly prominent mid and upper sky cover
until early afternoon, however a break in that sky cover is expected
through the peak heating hours, where temps are expected to surge
into the low 80s for many. Gustiness should peak during this stretch
with 20 to 25 mph expected to be common.

Later this evening, a convective complex is expected ahead of an
approaching cold front and should move into our western CWA between
8 and 11 PM EDT. From there, elevated convection is expected to move
eastward across our CWA. Not much change in the thinking with this
overnight convection as low level stability should mitigate larger
concerns for a severe threat. In addition to soundings showing the
stable layer in place, the latest HREF probabilities for any notable
ML CAPE values stays at 0% until right around sunrise in our far NW
CWA. So, pretty high confidence in any convection staying elevated
and the severe threat staying low. As previous forecasts have noted,
the overall shear profile will be quite high, and thus there is some
hesitation to completely rule out an isolated instance, but overall
not really concerned. SPC kept a Marginal risk for part of our
region, and think the best chance for any issues would be right
before sunrise across our NW CWA as those 40-50% probabilities for
around 500 J/KG of ML CAPE work into the area.

Some notable changes to the Wednesday forecast as confidence in
severe weather potential has lowered. Morning convection should
continue to push across our eastern CWA, well ahead of the trailing
cold front that will likely hang up just to our NW. Forecast
soundings through the afternoon show a pretty strong inversion just
below 700 mb, and recent runs of data have kept much of the
convective activity to our north across central IN into OH. Some
data does support convective activity along and north of the Ohio
River closest to the strongest forcing, which is also where SPC has
trimmed the Slight Risk significantly to just cover that area. Like
the idea of leaving the Marginal risk over the rest of the CWA for
the time being because the overall shear profile would still remain
quite favorable for some supercell storm modes if convection were to
fire, so don`t want to completely let the guard down yet. However,
current data appears to make it difficult for any parcels to reach
their LFC given the inversion, at least across the southern 2/3 of
our CWA. The bottom line here is that if the inversion does end up
as strong as currently advertised, then we might dodge a bullet for
much of our CWA. That being said, can`t let our guard down yet as
the inversion is the only limiting factor to what would otherwise be
a favorable environment for severe convection and likely some
supercell storm modes. Stay up to date of the latest forecasts over
the next 24 to 36 hours.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 409 AM EDT Tue Apr 16 2024

Synopsis...The medium range period will start by featuring Midwest
shortwave energy merging into a broad upper-level low over southern
Canada/northern Plains while positive upper height anomalies will be
found across the rest of the CONUS. The aforementioned upper-level
low will slowly move east the rest of the week, allowing associated
shortwave energy/mid-level jet to push a cold front through the
lower Ohio Valley Thursday night into Friday morning. For the
weekend, strong zonal flow aloft will continue over the region as
the Canadian upper low ejects to the northeast and shortwave energy
stream through the Great Lakes. At the surface, however, high
pressure over the Plains will usher in a cooler and more stable
airmass. Then, mid-level pattern amplification is anticipated for
the beginning of next week as Pacific shortwave energy punches
through a West Coast ridge and moves into the Central US possibly
phasing with East Coast trough.

Model Evaluation/Confidence...There is good model agreement between
deterministic model guidance regarding the large-scale pattern
evolution through next week. There are, however, a couple of
instances where models have shown certain degree of variability
that introduces lower confidence in the forecast. First one is
associated with the frontal passage Thursday night into Friday
morning and the position of a potential secondary surface low over
the lower Ohio Valley. Mos of the guidance (CMC/ECMWF/GFDL
SHIELD/NAM) have the surface low forming north of the Ohio River
while the latest GFS prompts it through KY. This could ultimately
influence the convective storm mode and the degree of mesoscale
forcing. The second one involves the pattern amplification early
next week, the timing of the frontal passage and overall
precipitation coverage.

Wed Night- Thursday...Rainfall and storm chances will be decreasing
through the night as dry air and low-level subsidence approach the
area behind the frontal wave. Thursday will start off dry with winds
quickly backing to the south pumping warm air advection to the area.
Depending on intensity, coverage, and duration of convection from
Wednesday, temperatures (lows and highs) might end up being a few
degrees warmer. Precipitation chances will increase from west to
east late in the afternoon as the next front approaches the region.

Thu Night - Friday...Another active period is expected Thursday
night into Friday morning as strong to marginally severe storms
might accompany the frontal passage. Based on consulted hi-res
guidance (NAM/GFDL Shield/RGEM), the strongest storms should move
across the area between 19/0 to 19/6Z arrange along a decaying line
of convection as instability will be dwindling farther east. Latest
SPC outlook highlights a Marginal risk of severe weather for the
entire CWA with Slight delineation in the western edge of the CWA.
Main weather hazard with this overnight activity will be isolated
straight-line winds. Rest of the day will be mostly cloudy with
lingering showers and gusty northerly winds. Moderate cold air
advection will account for highs in the 60s.

Weekend...Cold air advection regime will continue during the weekend
given persistence of breezy northerly winds and partly to mostly
cloudy skies. However, rain chances should decrease significantly as
surface high pressure will advect a subsaturated airmass in the low
levels.

Next Week...Monday should be dry and sunny with warming
temperatures. Although there is uncertainty on the track of the
shortwave and potential interactions with northern-stream trough, a
weak cold front appears to arrive on Tuesday or Wednesday raising
precipitation chances. Severe weather does not appear possible at
the moment given the lack of instability.

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 642 AM EDT Tue Apr 16 2024

Generally light SE winds will continue early this morning with
variable mid and upper level cloud cover. Some light precipitation
is working along the KY/TN border, but appears to be falling out of
high cloud bases, so unlikely to hit the ground or affect the BWG
TAF site.

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,
especially in the afternoon.

Steady to occasionally gusty winds could last into later tonight and
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. Some MVFR ceilings could arrive toward the end of this
forecast cycle, but confidence too low to mention at this time.

&&

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

&&

$$

SHORT TERM...BJS
LONG TERM...ALL
AVIATION...BJS