031
FXUS63 KPAH 210733
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
233 AM CDT Tue May 21 2024

.KEY MESSAGES...

- Mostly likely we stay dry until after dark today, but breezy.
  Then there is a small risk for severe storms (wind) in the
  overnight Tuesday.

- If instability can build Wednesday a respectable severe
  weather risk will emerge (wind and hail). As will a flash
  flood risk.

- Severe thunderstorm risks currently appear to peak on
  Wednesday and then again potentially on Sunday. But some type
  of severe storms may be possible each day Wed-Sun. Flash
  flooding may also develop any of those days and flash flood
  watches may be required later today or Wednesday.

&&

.DISCUSSION...
Issued at 233 AM CDT Tue May 21 2024

A sprawling low pressure system with 3 separate trough/jet max
elements sits over the northern Rocky Mountain region this
morning. A double barreled closed low sits over British
Columbia and Alberta with a jet max running down the Canadian
Pacific coast giving a nudge to everything that lies ahead. With
a trough axis over MT/WY and numerous embedded shortwave
troughs to the east with 110-120 kt jet maxima to the north and
south of a stronger shortwave over SD/NE. To the south of the
southern jet max over Texas a fairly strong elevated mixed layer
is being pulled in off the Mexican Plateau. While broad
southerly flow ahead of lee troughing is advecting mid 60s
dewpoints into much of the south central CONUS with 70 and even
80 degree dewpoints along the Texas Gulf Coast. CIRA hourly
precipitable water seems to suggest PWAT values in this area,
which will eventually head this way, are a little stronger than
the GFS has modeled currently. Locally moisture is increasing
through the column, although its definitely richer near the
surface, with a weak inversion at around 700mb that will likely
grow stronger as the day progresses today. As this giant mess
moves eastward a surface low will rapidly strengthen over the
upper midwest today and our mid- to low-level winds will
strengthen which will increase moisture advection and advect the
aformentioned TX EML over the region.

The net result will be a hot day that should remain mostly
precip free despite increasing low level moisture as the capping
inversion strengthens. Winds will pick up out of the south at
10-15 mph, enough for enhanced caution on area lakes.

Tuesday evening upper diffluence increases as the TX upper jet
max approaches. This starts work on lifting out our capping
mechanism. The HRRR and NAM seem to have a good grasp on the
thermodynamic situation where the GFS appears to be underdoing
the EML a little bit. This would result in convection initiating
along the cold front in western Missouri in the late afternoon
and then upscaling and trekking eastward, approaching the area
by late evening. Thermodynamic environment may be supportive for
some severe overnight mainly in the form of wind given fairly
strong deep and low level shear, but instability will be a big
question. New forecast has PoPs increasing after 05z and then
slowly tapering through 09z as large scale ascent weakens as the
nose of the jet max moves to our northeast.

We then get into the right rear quadrant of this jet after 21z
Wednesday. I think its possible given the richness of the column
moisture we maintain too much convection for surface heating to
yield much instability, but the more likely solution at this
point appears to be enough of a respite that we heay up into
the mid 80s with dewpoints in the upper 60s, particularly from
about Paducah southward. This would yield 2000-2500 J/kg of
MLCAPE with fairly strong deep layer and sufficient 0-3km shear
for a more organized wind threat. The tornado threat appears a
little more muted given projected 0-1km shear values. The NAM
and ECMWF and to some extent the GFS (although it is more
southeast of the area with this forcing) keep jet level lift
over the area with low level warm advection increasing though
the overnight making at least a few rounds of thunderstorms
(although probably only one round of severe potential)
possible. Column PWATs are projected at 1.6 to 1.7 and as
mentioned before the GFS may be running a little low with the
airmass in the western Gulf, so flash flooding may become a
headliner concern into the overnight. Its too early for a flood
watch but one may be required before all is said and done.

A fairly large discrepancy then builds into the guidance between
GFS/ECMWF members for Thursday with the GFS a little further
south with a shortwave that leaves us more dry on Thursday where
the ECMWF paints widespread thunder again. Given the column
moisture, rain/thunder looks very likely but the precip
magnitude and any flooding potential will rest on exactly how
that shortwave moves through. We remain in a stagnant pattern
with a front southwest to northeast just northwest of the area
in most guidance through Friday before it approaches in current
GFS/ECMWF guidance. Keeping rain and thunderstorm chances with
dewpoints in the mid 60s to near 70. Severe weather and flooding
potential could emerge on either of these days but
predictability is very low given the spread in guidance and the
fickle convective nature of the systems involved.

A stronger shortwave moves towards the area on Sunday spinning
up a strong surface low over MO/IL and tracking to our
northeast. GFS/ECMWF have been consistent for a couple of days
with this system both showing more potent mix of instability
and shear with a favorable synoptic scale pattern for a more
substantial severe weather threat. PWATs also rise up to
1.6-1.8 inches late in the day. This system as will be the case
with everything after tomorrow night though will absolutely be
influenced by coverage and intensity of thunderstorms in the
days preceeding it.

Essentially any day Wednesday through Sunday could see both
severe thunderstorm or flash flood warnings. I think the flash
flood threat has a higher ceiling overall but some decent wind
looks possible Wednesday if it comes together and we are going
to need to watch Sunday very closely.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 629 PM CDT Mon May 20 2024

The forecast is dry through Tuesday with VFR conditions
expected. Light winds overnight will increase to between 10-15
knots with gusts up to 25 knots in the afternoon.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Lake Wind Advisory from 10 AM this morning to 6 PM CDT this
     evening for ILZ075>078-080>094.
MO...Lake Wind Advisory from 10 AM this morning to 6 PM CDT this
     evening for MOZ076-086-087-100-107>112-114.
IN...Lake Wind Advisory from 10 AM CDT /11 AM EDT/ this morning to
     6 PM CDT /7 PM EDT/ this evening for INZ081-082-085>088.
KY...Lake Wind Advisory from 10 AM this morning to 6 PM CDT this
     evening for KYZ001>022.

&&

$$

DISCUSSION...JGG
AVIATION...AD