235
FXUS63 KLSX 101141
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
641 AM CDT Fri May 10 2024

.KEY MESSAGES...

- The next opportunity for showers and thunderstorms across much
  of the area is Monday and Monday night. Strong to severe
  thunderstorms are unlikely.

- Generally seasonable temperatures are expected through next
  week.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 342 AM CDT Fri May 10 2024

Upper-level northwesterly flow will remain in place over the Mid-
Mississippi River Valley through Saturday night, navigated by a pair
of troughs accompanied by very limited chances of rain. The first
trough is already passing overhead this morning, but associated
isolated to scattered showers have dissipated as they entered
northeastern MO and west-central IL as marginal instability
decreased and low-level forcing remains negligible. Therefore, dry
conditions will prevail today as shortwave ridging briefly builds in
the wake of the trough. With a seasonably cool airmass in place
behind last evening`s cold front and prevalence of scattered to
broken stratocumulus/cumulus, temperatures are expected to be
slightly below average today with high temperatures in the mid-60s
to low-70s F.

The next trough will arrive tonight, forcing a weak cold front
through the CWA. The strongest large-scale ascent and frontal
moisture convergence will pass to the north and northeast of the
CWA, but enough forcing may available for isolated showers along the
front in northeastern MO and west-central/south-central IL. Post-
frontal CAA will be short-lived and insolation will be abundant on
Saturday, resulting in a warming trend through Saturday with
temperatures near average.

Pfahler

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 342 AM CDT Fri May 10 2024

Global deterministic and ensemble model guidance are in general
agreement with an eastward ejection of an upper-level closed low
from the Rocky Mountains to the Mississippi River Valley on Monday
that will both interrupt the northwesterly flow and provide a more
robust opportunity for showers and a few thunderstorms. There are
differences in the exact structure and timing of the trough along
with associated surface cyclone track, but at least a period of
showers is expected for most of the CWA between Sunday evening
and Tuesday with ensemble model 24-hour probabilities of QPF
greater than 0.10" over 80 percent CWA-wide. Probabilities of QPF
greater than 0.50" are 40 to 50 percent along and south of I-70,
closer to the mean surface cyclone track and associated warm
sector with marginal instability and the best chance of
thunderstorms. The potential for any strong to severe
thunderstorms appears low with probabilities of more than 1000
J/kg of SBCAPE less than 10 percent and deep-layer wind shear not
progged to be particularly strong. Ahead of the trough, low-level
southerly flow is anticipated to warm temperatures to just above
average on Sunday, but the impact of clouds and precip on Monday
is uncertain with the NBM high temperature interquartile range
nearly 10 F.

Disparities in global model guidance increase through the rest of
next week, especially with the amount of upper-level ridging across
the western CONUS, but there is at least a signal for another trough
to pass over the Mississippi River Valley Thursday into Friday
before differences upstream become a more significant impact. A
large portion of ensemble model guidance have showers and
thunderstorms in the CWA with this trough at some point in that
timeframe. Otherwise, after temperatures cool again to slightly
below average again by Tuesday, but increasing spread in the NBM
interquartile range thereafter demonstrates a question in whether
temperatures warm to average or above average.

Pfahler

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 640 AM CDT Fri May 10 2024

A range of flight conditions are present this morning across the
region due to patches of MVFR stratocumulus, most prevalent at St.
Louis metro terminals, and IFR fog at KUIN. However, flight
conditions are expected to improve through the morning as fog
dissipates and stratocumulus lifts to VFR. VFR flight conditions are
then anticipated to persist through the end of the TAF period,
despite a weak cold front passing through the region overnight. An
isolated shower cannot entirely be ruled out, but the main impact of
the front will be a wind shift from southwesterly to northwesterly.

Pfahler

&&

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

$$

WFO LSX