038
FXUS63 KLSX 141138
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
638 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
shows 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) Wednesday 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 slowly
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. Medium range deterministic
guidance shows moisture return with dewpoints in the 60s advancing
northward through midweek. LREF mean CAPE values, while not
terribly high (1000 J/kg), do indicate that instability moves
into sections of southern Missouri by Thursday morning.
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 pattern remains active into Friday with a trend toward above
normal warmth heading into next weekend.


Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 617 AM CDT Tue May 14 2024

A broad area of low pressure will continue to rotate through the
region from west to east today. Low level saturation and weak
surface flow has given rise to some visibility restrictions and
low ceilings. There have been a range of observation with mostly
MVFR/IFR around this morning. Showers will become more numerous
through late morning into this afternoon and while thunder has not
been common this morning, there is the potential for a few
thunderstorms this afternoon. Localized heavy rain may accompany
thunderstorms on occasion with direct impacts resulting in greater
visibility reductions than what is currently in the prevailing
groups. Given the localized nature of the heavier activity, it is
likely to be best handled with later amendments as conditions
materialize.

Precipitation will gradually fade after sunset, especially as the
system pulls off to the east. Low end MVFR/IFR ceiling and
visibilities linger around through tonight.


Maples

&&

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

$$

WFO LSX