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000
FXUS63 KLSX 221930
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
230 PM CDT Mon Apr 22 2024

.KEY MESSAGES...

-A weak cold front will bring a round of showers and perhaps a
 weak thunderstorm or two during the day tomorrow.

-Confidence is high that multiple rounds of showers and
 thunderstorms will occur between late Thursday and late Sunday,
 along with well above average temperatures.

-Severe storms are also possible at times late in the week, but
 confidence is low regarding this potential.

&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 226 PM CDT Mon Apr 22 2024

As we begin the work week, a broad area of surface high pressure
continues to slowly drift southeastward, now encompassing much of
the Ohio Valley and deep south. This places the lower Missouri river
basin within a regime of southwesterly low level flow, which is
driving breezy and warm conditions. Afternoon temperatures are
likely to top out near 70 degrees, and persistent southwesterlies
will prevent temperatures from falling quite to the levels we`ve
seen the past few mornings. As such, frost will not be a concern
tonight, with morning lows likely bottoming out in the upper 40s to
low 50s.

During the day tomorrow, a shortwave trough will move across the
upper midwest, sending a weak cold front south and through the
forecast area. This front will bring a modest cooldown tomorrow for
all but our southernmost Ozark counties, along with a round of
showers. Instability will be marginal, both pre-frontal and post-
frontal, with MUCAPE values projected to reach near 500 J/kg at most
and more likely less than that. Still, this may provide just enough
oomph for a strike of lightning or two, particularly during the
afternoon across parts of Illinois when instability is maximized.

BC

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 226 PM CDT Mon Apr 22 2024

Following Tuesday`s cold front, surface high pressure and northwest
flow will return across the region, maintaining seasonally average
temperatures and dry conditions Wednesday.

By Thursday, while an upper ridge will begin to build overhead, a
deepening trough will dig into the western U.S. and a series of
shortwaves will pivot around its base and into the central plains:
first on Thursday/Friday, and another late in the weekend. As this
occurs, deep southerly flow will draw increasingly rich moisture
northward into the lower Missouri basin, setting the stage for a
wet and active end to the week and weekend. This will include the
potential for thunderstorms, which appear increasingly likely at
various times throughout this period. This pattern is also likely
to yield strong to severe thunderstorms regionally, but it
remains to be seen whether this will occur within our forecast
area of responsibility, and the initial threat of severe weather
appears to be focused to our west late in the week.

While the potential for strong/severe storms remains somewhat
nebulous, confidence is high that multiple rounds of rain will occur
between roughly Thursday night and Sunday night. This will be
roughly spread out across two semi-discrete time windows...the first
being between Thursday night and Friday night when a shortwave and
associated surface low move across the upper Midwest to our north,
and the second being sometime between late Saturday and late Sunday
as a second shortwave follows a similar track. Many timing/track
details remain unresolved, but there is a clear signal for anomalous
moisture during this timeframe, and ensemble members are nearly
unanimous that widespread precipitation will occur at some point
during those few days.

Meanwhile, a steady warming trend is also expected late in the week,
with well above average temperatures likely to develop by Friday and
persist into the weekend, and likely beyond in spite of the passage
of a weak cold front early in the week.

BC

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1215 PM CDT Mon Apr 22 2024

VFR conditions are expected throughout the 18Z TAF period. Gusty
southwest winds will persist through the remainder of today,
overnight, and into tomorrow morning. A cold front will move
through the area tomorrow afternoon, switching winds to the
northwest and bringing with it a round of showers. This will occur
near the end of the TAF period, and ceilings may dip to MVFR
levels at times. A few strikes of lightning are also possible, but
confidence remains too low to add to the TAFs just yet. This may
change in future updates if greater confidence can be achieved.

BRC

&&

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

$$

WFO LSX