000
FXUS63 KPAH 141103
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
603 AM CDT Sun Apr 14 2024

.KEY MESSAGES...

- Warm weekend weather will continue with highs into the 70s to
  lower and mid 80s.

- There is a chance for strong to severe thunderstorms late
  Tuesday into Tuesday night and again Wednesday

- Cooler temperatures are forecast next weekend.

&&

.DISCUSSION...
Issued at 156 AM CDT Sun Apr 14 2024

It was a very pleasant Saturday across the quad-state today with
rigging aloft over the central US and sfc ridging extending
across the southeastern US. Similar conditions, perhaps a few
degrees warmer are forecast for Sunday. Skies should be mostly
sunny with a few cumulus bubbling up in afternoon heating. A
malcontent sits just off the California coast this morning in
the form of a broad closed low that is very slowly moving
towards the US interior. By Monday afternoon that low is
forecast to be positioned over the intermountain west with lee
cyclogenesis starting up over the Front Range that tightens up
our low level flow and strengthens moisture return. Warm
frontogenesis is forecast over our northern counties, or
slightly to the north Monday afternoon, which will reintroduce
some chances of thunderstorms through early evening. A broad
height fall regime through the overnight and early part of the
day Tuesday will keep a small rain/thunder chance in the
forecast through Tuesday.

By Tuesday afternoon our original problem low has emerged into
the central Plains with a 110-120 kt jet streak wrapping around
its south and southeast, emptying over Missouri. A surface low
rapidly deepens over the Plains through the day Tuesday, with
deterministic and ensemble solutions plotting 989-991 mb by
afternoon over Nebraska. Our low level flow responds with 850mb
flow increasing to 40 kt through the day. Diffluence on the left
front edge of the approaching jet max appears to create low
level pressure falls that shift our surface winds more
southeasterly. As modeled currently this shifts us to pull from
air over the Tennessee Valley which is showing 56-58 degree
dewpoint air, having mixed down drier air from 850-700mb from
antecedent ridging. This keeps instability more muted through
the day Tuesday. As the larger storm system begins to approach
from the west our winds shift more southerly, pulling from 62-65
degree dewpoint air and our instability ramps up after dark.

Through the overnight Tuesday 850mb flow increases to 55-65 kts
on GFS/ECMWF/NAM projections. With upper level flow increasing
we move into the 06z timeframe with something on the order of
55-60 kts of deep layer shear and 30-40 kts of 0-1km shear,
yielding large looping hodographs with 0-1km SRH on the order of
250-300 m2/s2. An elevated mixed layer then looks to move in
overtop of our region through the overnight. In current model
guidance this feature does not really add much of a capping
inversion, but just adds to dry air aloft and steepens our
midlevel lapse rates. I suspect the capping may be underdone in
the modeling. If convection has not yet initiated this may serve
to make CI harder both through capping and dry air intrusion
into developing updrafts. But an EML overspreading established,
highly-sheared convection can be a volatile mix, particularly
in the overnight hours. Shear begins to relax a bit after
sunrise but we retain a fair amount of MLCAPE through 18z or so
when the front clears the area. The front is continuing to trend
ever so slightly slower as well run-to-run.

Bottom line, there are thermodynamic issues, both in terms of
moisture return and the timing and impact of mid-level
capping/dry air. However given the modeled large-scale ascent
and higher-end shear parameter space overnight Tuesday this
event deserves our close attention over the next 72 hours for an
all- hazards threat that would appear to evolve into a more
wind/hail threat after sunrise Wednesday.

A strong zonal jet establishes over the northern CONUS through
the rest of the week knocking a cold front cleanly through the
region and leaving us in cooler and drier air overall. GFS/ECMWF
both spin a little shortwave through Thursday afternoon and
start to work a warm front towards the region for the weekend,
but the run-to-run continuity on these features have been fairly
poor. Given the synoptic picture I would lean towards a cooler
and drier picture overall through the weekend for now.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 603 AM CDT Sun Apr 14 2024

Low-level wind shear conditions will persist until mixing builds
up over the next couple of hours with winds becoming gusty at
the surface. VFR conditions are forecast through the day and
overnight. Wind should diminish overnight Sunday night.

&&

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

&&

$$

DISCUSSION...JGG
AVIATION...JGG