227
FXUS63 KLSX 140910
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
410 AM CDT Tue May 14 2024

.KEY MESSAGES...

- Numerous showers and a few non-severe thunderstorms are expected this
  afternoon into early this evening. Thunderstorms could produce
  locally heavy rainfall.

- Mainly dry conditions are expected during the day Wednesday with a
  slight moderation in temperatures. Active weather returns late
  Wednesday night and extends through at least Friday.

- Above normal temperatures return next weekend.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 409 AM CDT Tue May 14 2024

The upper level trough and associated mid-level low will move
eastward through the region today with multiple pieces of
vorticity rotating around the low. Low level moisture remains in
place with surface dewpoints in the low to mid-60s across much of
Missouri and Illinois. A weak surface front continues to move
southeast through the region this morning with northwesterly flow
behind the system pulling in slightly cooler air.

As we head into this afternoon, a broad pool of 500-1000 J/kg SBCAPE
builds over the region with pockets slightly above 1000 J/kg. Higher
values of 1500-2000 J/kg remain southeast of the CWA ahead of the
low center and advancing surface front. CAMs show numerous showers
and a few thunderstorms dispersed across the region through the
period of diurnal peak heating. Embedded within the broader field of
showers is an east-west oriented area that starts out along an north
of I-70, where relatively greater coverage is likely driven by mid-
level forcing at the northern fringes of the mid-level low. Shear
profiles are even weaker than yesterday, lending to less support for
organized convection. However, PWATs do remain high with values of 1-
1.5 inches signaling that what thunderstorms do materialize could be
efficient rain producers on a localized scale. PMM/LPMM guidance
show small striations of 1.5-2 inch amounts largely running along
and east of the Mississippi River, which could lead to ponding in
poor draining areas and/or locations saturated by recent rainfall.

A few showers could linger over interior sections of Illinois (far
eastern CWA) early Wednesday morning as the system slowly exits to
the east. Otherwise, an inverted surface ridge that extends
southwest from the Great Lakes is sandwiched between the departing
system to the east and another system over the Plains. Upper level
ridging builds in from the southwest, offering a break between
activity with dry weather and a slight moderation in
temperatures Wednesday.


Maples

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 409 AM CDT Tue May 14 2024

An upper level trough is progged to extend from the northern Plains
through the southwestern CONUS by midweek. Multiple shortwaves are
present in the broader synoptic pattern with a cutoff low slowing
moving west to east over southern California. This pattern continues
to hinder the forecast with some uncertainty stemming from the
complicated evolution and placement of each feature and their
associated boundaries.

The area to watch will be across the central Plains, where upper
vorticity is kicked northeast ahead of the southwestern upper low.
Surface low pressure develops at the lee side of the Rockies and
lifts a warm front into the region out of the southwest late
Wednesday night into Thursday morning. LREF mean CAPE values, while
not terribly high (1000 J/kg), do indicate a trend in northward
advancement of instability into southern sections of Missouri by
Thursday morning. Medium range deterministic guidance shows moisture
return with dewpoints in the 60s advancing northward. Meanwhile, the
low level jet strengthens over eastern sections of the Plains as
MUCAPE values reach 2500-3000 J/kg and shear values between 40-50
knots over southern Missouri. While the finer details with regard to
placement and timing are still in question, trends are favoring
Thursday for active weather. Given the deterministic values, there
is some indication that stronger thunderstorms could be in the
offing once again. How this all plays out will have impact farther
down the line in time with placement of the surface features. That
said, it does look like the overall patter remains active into
Friday with a trend toward above normal warmth heading into next
weekend.


Maples

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1033 PM CDT Mon May 13 2024

Lots of moisture still lingering across the area tonight as a
broad low pressure system slowly tracks near the region. Multiple
subvortices have brought rounds of showers and embedded
thunderstorms, though these may not be as widespread as previously
thought. Conditions are variable across the region from VFR to
MVFR, but the trend will be for conditions to worsen overnight as
ceilings lower. With so much moisture around and subtle low level
lift with the low, we couldn`t rule out some light fog or drizzle
as well, but lower ceilings at least look likely. We`ll see some
improvement Tuesday morning, but another round of afternoon
showers and thunderstorms is expected just about area wide as
winds become northwesterly on the back side of the finally
departing low.

Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX