341
FXUS63 KLSX 142336
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
636 PM CDT Tue May 14 2024

.KEY MESSAGES...

- Showers and isolated thunderstorms will diminish this evening
  and exit to the east overnight. Isolated instances of heavy rain
  are possible through this evening.

- Active weather will return late Wednesday night and continue
  through at least Friday with periods of showers and
  thunderstorms impacting parts of the area, including the
  potential for strong storms Thursday afternoon and evening.

- Above normal temperatures return next weekend and continue into
  early next week.



&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 225 PM CDT Tue May 14 2024

The slow-moving upper low was located over central MO at mid-
afternoon. More continuous/banded showers and scattered
thunderstorms were located in advance of the low stretching from
far southeast MO through southwest and west-central IL, while
further west more diurnally driven scattered showers and isolated
storms were rotating cyclonically about the mid-upper circulation
feeding off SBCAPE of 1000-1500+ J/KG. The aforementioned band
will continue to shift slowly east through the remainder of the
afternoon bringing some locally heavy downpours and pockets of
heavy rain, owing to more persistence and a very moist air
mass/higher rain rates. The trend heading through the early-mid
evening should be a decrease in coverage of showers/thunderstorms
as the diurnally driven instability wanes and the upper low moves
to the east-southeast. All of the precipitation should exit the
area overnight as the upper low moves into the Ohio Valley.

Stratus is expected to hang tough across the area overnight and
any breaks could result in locally areas of fog. All-in-all, a lot
of cloudiness is expected to persist on Wednesday. The stratus
will diminish as clouds become more cumuliform heading into the
afternoon, with below normal temps.

The active weather regime will then resume late Wednesday night.
A broader trof will move into the upper MS Valley with a well-
defined vort max tracking into the area overnight. This
disturbance along with a returning warm front and increasing
southwesterly LLJ should support showers and thunderstorms moving
into at least central and portions of eastern MO between 06-12Z
Thursday. The activity could be weakening convection originating
from the central Plains and/or additional elevated development.

Glass

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 225 PM CDT Tue May 14 2024

The expectation is showers and thunderstorms will be ongoing at
daybreak Thursday, probably west of the MS River, supported by the
aforementioned mid-level disturbance and LLJ. This activity will
likely move east across the CWA through the morning with potential
for additional development trailing in its wake. Later on Thursday
afternoon and night, the presence of a lingering east-west
boundary across the southern part of MO and southern IL is likely
to be the catalyst for additional rounds of showers and storms
with MLCAPE forecast from 1500-2500 J/KG. Sufficient deep layer
shear on the order of 30 kts should be present to support
potential for organized storms, including a few strong-severe
storms.

The forecast for Friday into early Saturday is a bit more muddled.
There are differences in the upper level trof structure/position
and timing with a trof translating eastward from the southwest
U.S. across the Plains which adds uncertainty to the forecast.
Most of the guidance shows only nebulous forcing Friday and a
lack of a surface boundary but plentiful instability, at least
supporting a threat of showers and thunderstorms. I suspect that
this trof will have passed to the east by early Saturday and the
majority of the weekend will be dry with a warming trend.
Differences in details of the large scale regime persist into
early next week. There is good agreement the flow aloft will
become more southwesterly with potential short waves tracking
within it bringing more thunderstorms chances, but uncertainty is
high in the timing and details. Temperatures should return to
above normal this coming weekend and continue through early next
week.

Glass

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 624 PM CDT Tue May 14 2024

A cluster of showers and a few thunderstorms just went up over the
St. Louis metro, but overall, precipitation across the area will
diminish in coverage and intensity over the next few hours. Clouds
will linger after the precipitation ends, gradually filling in
and lowering through the evening. The vast majority of forecast
guidance has cigs dropping below 1000 ft at all terminals, though
NBM MOS guidance does indicate lower probs of IFR conditions than
other models, so I`ve narrowed the IFR window slightly. Reduced
flight conditions will linger through much of the morning,
gradually improving back to VFR by mid day.

Specifics for KSTL:
The weak thunderstorm just to the east of the terminal is very
slowly sliding westward and will likely impact the terminal with
at least rain and MVFR visbys in the next 10-20 minutes. I`m not
confident that thunder will impact the terminal, so I`ve stuck
with just VCTS in the prevailing group. Precip should not linger
long after sunset.


BSH

&&

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

$$

WFO LSX