497
FXUS63 KPAH 221722
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1222 PM CDT Wed May 22 2024

.KEY MESSAGES...

- Severe thunderstorms possible today, with hail the leading
  threat. Some wind damage potential may develop in the
  afternoon. At least some potential that storms are unable to
  initiate in the afternoon. Heavy rain can be expected with any
  storms that form.

- Scattered to occasionally numerous storms are possible
  Thursday through Saturday. The tendency will be for peak
  coverage in the afternoon, but very subtle jet-level waves
  could spark things any time through the holiday weekend.

- Sunday remains the best potential for more organized and
  widespread severe weather. There are timing and detail
  discrepancies between models, as you would expect, but we will
  need to keep a close eye in the coming days.

&&

.DISCUSSION...
Issued at 218 AM CDT Wed May 22 2024

Subsidence from the right front quadrant of an approaching jet
maximum seems to be winning the convective coverage game
tonight. Widely scattered thunderstorms are trending downward
over the quad-state while there is some new development over
south central Missouri that appears to be initiating in an area
of strong lower-level frontal convergence. Based on observed and
model soundings believe this convection is partially elevated
with about 1500 J/kg of CAPE rooted at 800mb or so to work with.
This activity may pose a hail threat over the next couple of
hours. The overall picture though is subsidence increasing a
capping inversion through early this morning. Most of the
guidance generates enough convection to skew the thermodynamics
but I *think* we will see enough sun to warm into the middle 80s
as a capping inversion strengthens over the area.

If you modify soundings this afternoon to about 84 degrees with
a 70-73 degree dewpoint you get about 2500 J/kg of MLCAPE. The
cap holds against unforced parcels but there may be just enough
frontal convergence to initiate convection this afternoon,
helped perhaps by a little bit of height fall via a shortwave
passing over IA/IL. Shear is relatively light in the 0-3km
layer which may make parcels a little less susceptible to dry
air entrainment, but coverage will probably be limited by a
pretty neutral jet-level ascent environment. I think what we
will probably have is a supercells or nothing scenario. Hail
looks to be the headliner threat with wind also accompanying it.
Upscaling into more linear features is possible but doesn`t
look extremely likely. Tornado threat appears muted given the
low level shear environment. Very heavy rainfall will be a
threat as storm motion may be fairly slow given the weak shear
environment and PWATs remain above 90th percentile
climatologically.

The front stalls over the area Thursday through Saturday and we
will be mostly at the mercy of daytime heating and very small
perturbations in the flow aloft which will be extremely
difficult to identify and time. Kept a broad shower and
thunderstorm chance. Given the moisture and instability present
heavy rain and isolated severe weather looks possible each
afternoon.

Sunday still looks potentially concerning, although some spread
in the GFS/ECMWF timing of a subtle lead shortwave trough ahead
of a stronger closed low over the intermountain west would
likely result in big differences for our total severe threat.
the ECMWF merges this leading shortwave with the broader
troughing creating a sort of negative tilt longerwave trough
from MO to ND which results in a stronger surface low and faster
frontal passage. Where the GFS keeps the systems separate,
leading to a slower frontal passage. Both models though show
strong westerly shear at a sharp angle to the existing front,
with 850mb flow ramping up to 35-45 kts in the late morning and
afternoon with dewpoints in the 70s. The GFS leading wave
scenario opens the possibility for warm sector initiation with
MLCAPEs at 3000 J/kg with 0-1km SRH over 250 m2/s2 with a front
cutting into slightly less, but still respectably strongly
sheared air. The ECMWF initiates convection earlier owing to the
faster progression and doesn`t let peak heating quite arrive but
still shows a concerningly volatile airmass ahead of the
activity that does develop. Lapse rates below 700mb though are
pretty weak in GFS soundings owing it looks like to warmer and
drier air mixing in from the southwest and it will be important
to see how those details develop as well.

Once the front clears Monday, which looks dry, another shortwave
pulls up on Tuesday which may give us some thunder chances,
particularly across the south.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1216 PM CDT Wed May 22 2024

Tricky forecast today with lower confidence in the TAFs. Storms
are beginning to develop just south of the KY state line and
will continue to develop through the day today. Storms are also
expected to develop over SEMO and move east later this afternoon.
These are the storms that are expected to affect the terminals
at some point through the evening and overnight. Cig heights
will vary across the area and within storms but could mostly be
MVFR.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.

&&

$$

DISCUSSION...JGG
AVIATION...SHAWKEY