Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 131946
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
246 PM CDT Wed Mar 13 2024

.KEY MESSAGES...

- Warm temperatures continue, but an approaching storm system
  will bring isolated thunderstorms through Thursday. More
  numerous/a line of storms are forecast Thursday night. This
  activity will have a risk for damaging wind/hail and isolated
  tornadoes. Heavy rain may lead to localized flooding.

- Thursday will be breezy with southerly winds. Wind gusts
  between 25 to 35 mph are possible through the afternoon.

- Relatively benign weather is then forecast before the next
  cold front Sunday night that will likely knock overnight lows
  back below freezing for a couple of days.


&&

.DISCUSSION...
Issued at 246 PM CDT Wed Mar 13 2024

Very springlike day across the region. A few spots of shallow
cumulus with some rain showers but otherwise sunny and warm with
temperatures rising into the mid 70s. A warm front is trying to
become a bit better defined overhead as a surface low spins up
over the Plains. A broad area of upper diffluence exists over
the central Plains ahead of a trough/closing low that is
stalled west of the Rocky Mountains.

Tonight that warm front should become better defined and
frontogenetic forcing may aid in initiating some showers and
thunderstorms over southern Illinois and northern southeast
Missouri. There is a little bit of elevated instability for
thunder, around 500-800 J/kg but the net jet pattern will be
convergent in the right front quadrant of a 110 kt jet max
running ahead of the stalled trough. In general I think most of
the activity will be confined to fairly close to the front and
mostly stay northwest of the area tonight.

Thursday the pattern amplifies and south to southwesterly
lower-layer flow increases. This pulls in richer moisture with
dewpoints increasing into the mid 60s by the afternoon. An
elevated mixed layer evident on 12z RAOBs over Texas works
overhead building in a capping inversion at around 850mb while
simultaneously steepening 3-6 km lapse rates to around 8.0 C/km.
Wet bulb zero heights for hail will be around 9000-9500 ft and
as the heating of the day works with increasing lower level
moisture we end up with 1800-2500 J/kg of mixed-layer CAPE. We
stay in a net-convergent upper jet position until about 2-3 pm.
Its possible a few showers and storms spark on a residual
700-800mb boundary that would have some elevated instability to
work with but for the most part right now it looks to stay dry
through much of the late morning and afternoon.

Thursday afternoon and into the evening a weak shortwave
enhances the jet over the southwestern Great Lakes region and
the right-rear quadrant of this jet increases large scale ascent
over MO/AR right at peak heating. This develops a weak low-level
cyclone over IL/MO that strengthens our low-level winds and
nudges a cold front further east, but also aids in initiating
convection. 0-6km shear is about 50-60 kts at this point, with
0-1km shear about 20 kts with a little bit of weakness at the
3km layer. Although we will need to watch for a little bit of
isallobaric backing in the low level windfield - which would
enhanced low level SRH. Most CAMs seem to initially develop
discrete supercells to the west of the PAH forecast area that
quickly upscale into an MCS and trek eastward. This seems
plausible given the relatively strong forcing. The shear is not
out of the park, but sufficient for a wind damage threat and any
supercells that form, or bowing segments that catch the right
whiff could produce a tornado threat. Our SEMO counties appear
for now to be the best positioned for a higher severe weather
threat overall but instability would be sufficient for the risk
to persist across much of the area. This is reflected in the
new SPC SWODY2 that essentially has the entire area in a wind-driven
SLGT risk for an MCS pushing east across the area in the
evening and early overnight.

Upper troughing takes a long time to organize to our northwest
and the surface front doesn`t really make it completely through
the area until after daybreak. The outright severe thunderstorm
risk should wane fairly quickly in the evening, particularly if
an organized line were to form - however a heavy rainfall threat
may persist through the overnight. Right now guidance has that
risk to our southwest but HREF PMMs of 3-5 inches are
apparently in the 12z runs over northern Arkansas. With PWAT
values around 1.5 inches and the possibility of extended periods
of convective rain we will need to be alert for the potential
for some flash flooding as well, although the risk appears too
low for a flash flood watch right now.

Once the front moves through Friday morning the next topic of
note is a fairly strong cold front Sunday night. The front pulls
in an arctic airmass that will likely see lows dip near or below
freezing both Sunday night and then more likely on Monday night
as surface high pressure sets up over the area. Return flow
rebounds fairly quickly Wednesday to moderate temperatures once
again.


&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1113 AM CDT Wed Mar 13 2024

A few scattered cu with bases around 4000 ft or higher will
remain possible through the afternoon with very isolated
showers. Winds will be moderate out of the south-southwest
gusting to 13 to 17 kts. Light wind and VFR conditions are
anticipated much over the overnight with an MVFR ceiling
developing just before or around dawn with winds picking back up
as well.

&&

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

&&

$$

DISCUSSION...JGG
AVIATION...JGG


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