103
FXUS63 KLSX 021733
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1133 AM CST Mon Mar 2 2026

.KEY MESSAGES...

- Multiple opportunities for showers and thunderstorms are
  expected this week with beneficial rainfall across the area. It
  is not yet clear if thunderstorms will pose any hazards (i.e.,
  severe weather, flash flooding).

- After today, temperatures will warm to above average with
  confidence high in Friday being the warmest day.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 353 AM CST Mon Mar 2 2026

The Winter Weather Advisory has been canceled early this morning due
to any potential accumulating wintry precipitation coming to an end.
Very light accumulations of snow and sleet have been reported on
grassy and elevated surfaces along/north of I-70 and especially
across northeastern MO/west-central IL. With temperatures near 32 F,
there could be some slick spots through daybreak but the wintry
precipitation has been relatively unimpactful. Low/mid-level FGEN
was more transient and a low-level warm nose quickly advanced
northeastward overnight, severely limiting the window of snowfall
rates high/persistent enough for higher accumulations and any
impacts.

Rain, possibly mixed with sleet, will gradually come to an end
across southeastern MO and southwestern IL, likely ending as drizzle
through 15z with forcing and moisture become shallower. Aside from
some additional patchy drizzle this afternoon, mostly dry conditions
are expected today, but clouds will continue blanketing the CWA. The
diminished insolation and minimal WAA will only allow temperatures
to slowly reach the 40s F by this evening. With some cooling of the
boundary layer tonight, light winds, and a sinking low-level
inversion forcing stratus closer to the surface; some fog is
possible after sunset. However, HREF probabilities of visibilities
1/4 mi or less are generally under 20 percent, lowering confidence
in this fog becoming dense.

Through 04 to 07z tonight, CAMs and short-term model guidance are in
agreement that numerous showers and a few weak thunderstorms (MUCAPE
of up to 500 J/kg) will blossom near central MO and subsequently spread
northeastward as low to mid-level isentropic ascent and moisture
increase at the nose of a LLJ intersecting a warm front. However,
by Tuesday afternoon, the warm front is generally expected to
stall near the I-70 corridor, with showers and thunderstorms
continuing at times within low-level forcing along the front and
to the north. With this front bisecting the CWA, there will be a
stark contrast in high temperatures with 50s F to the north within
persistent cloud cover and frequent precipitation, and 70s F to
the south where there will be low-level WAA and less clouds. Near
the I-70 corridor, confidence is lowest in temperatures with high
sensitivity in the position of the front captured by greater
spread in the NBM interquartile range, although largely in the 60s
F.

Pfahler

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 353 AM CST Mon Mar 2 2026

The overall wet and active weather pattern will persist through the
end of the week as upper-level zonal flow transitions toward
southwesterly across the Mid-Mississippi River Valley as longwave
troughing emerges over the Rocky Mountains. There will be a parade
of shortwave troughs that navigate the flow, but model guidance
varies in how the handle these features, dictating when the highest
chance of showers and thunderstorms will be along with determining
the potential for any associated hazards (i.e., severe weather or
flash flooding).

A pronounced shortwave trough is progged to pass sometime between
Wednesday and Thursday; however, there is still a large amount of
spread on its timing and amplitude, determining when a surface low
develops, how strong it becomes, and whether or not a trailing cold
front can pass through the CWA by Thursday and lead to a relative
break in rain chances. Additionally, increasing anomalous PW
(nearing the 99th climatological percentile), deep-layer flow
paralleling the preceding warm front draped across the CWA, and a
broad LLJ intersecting the front, all support rounds of showers and
thunderstorms that could train near that front across the CWA.
Exactly how long this pattern persists will be determined by the
arrival of the shortwave trough/surface low. If it continues into
Thursday, the threat of heavy rainfall will increase. Accordingly,
the ECMWF EFI/SOT does highlight this time period for potentially
extreme rainfall, with much of the EPS membership having a slower
shortwave trough/surface low arrival. Another important
consideration will be that soils need to be significantly moistened
before flash flooding can become a concern, which will rely on the
magnitude/location of rainfall on previous days. Anything before
that point will just be beneficial rainfall. The threat of severe
thunderstorms is also uncertain with questions in how far northward
into the CWA surface-based instability can reach with concerns for
quite a bit of clouds and precipitation to be present. Ensemble
model-based probabilities of SBCAPE of 750+ J/kg only reaches 20
percent along/south of the Missouri River on Wednesday (lower on
Thursday).

Friday into Saturday, the upper-level flow pattern is forecast to
become increasingly amplified with deep with a ridge also building
across the eastern CONUS. This pattern would favor any front
leftover from previous days to quickly lift northward early Friday,
which could be the only catalyst for the greatest chances of showers
and thunderstorms early in the day. Although probabilities of SBCAPE
750+ J/kg are higher (20 to 40 percent) on Friday, current forecast
soundings indicate that there may be a capping inversion across the
open warm sector, limiting the potential for showers and
thunderstorms developing during the afternoon when instability is
greatest. With drier conditions and the warm sector in place,
confidence is high that Friday will be the warmest day of the week
and NBM probabilities of high temperatures 80+ F are 40 to 70
percent along/south of the Missouri River. It is not until Friday
night into Saturday, the majority of ensemble model guidance have
the chance of showers and thunderstorms increase as an upper-level
trough and associated cold front reach the CWA. With potentially
unfavorable diurnal timing of these showers and thunderstorms
confidence in severe thunderstorms is still low; however, the threat
of heavy rainfall will need to be monitored if less progressive
solutions of the front advancement become more popular. Lastly, the
speed of this front will also determine when and how much of the CWA
is cleared of the chance of showers and thunderstorms Saturday and
Sunday.

Pfahler

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1128 AM CST Mon Mar 2 2026

IFR flight conditions will persist through the TAF period due to
persistent low ceilings. Drizzle is forecast to shut off early
this afternoon, and winds will become variable tonight. After
midnight, rain will move into the region impacting all terminals
and potentially dropping conditions to LIFR at times. Rain is
expected to exit in the middle of the morning with a chance of
rain persisting through 18z. Ceiling improvement to MVFR and
additional rain are forecast just outside of the period.

Jaja

&&

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

$$

WFO LSX