644
FXUS63 KLSX 211721
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1221 PM CDT Fri Aug 21 2026

.KEY MESSAGES...

- There is a slight chance for showers and thunderstorms tonight
  into early Saturday morning. Otherwise, dry weather is
  expected into the weekend with temperatures mainly in the
  80s.

- Near to slightly below normal temperatures are expected next
  week. There are low chances for rain late Sunday night through
  Monday night, and again toward the middle and end of the week..

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 401 AM CDT Fri Aug 21 2026

A high amplitude upper level pattern with a ridge centered near the
Four Corners Region and a trough just east of the Mississippi
Valley.  The trough continues to amplify over the Great Lakes and
Ohio Valley today through Saturday which brings another cold front
into Illinois and Missouri late tonight.  Short range guidance shows
moisture pooling ahead of the front this afternoon and evening which
produces 3000+ J/Kg CAPE.  However, forecast soundings across our
area show a significant amount of CINH, so thunderstorm development
looks very unlikely this afternoon and evening.  With that in mind,
most models including CAMs show a cluster of convection developing
over northern Illinois and/or eastern Iowa this evening in the
unstable airmass where the cap isn`t as strong.  This cluster moves
south-southeast and could potentially graze northeast Missouri and
west central Illinois into south central Illinois before it
dissipates overnight.  However, most guidance keeps the
thunderstorms out of our area due to the strength of the cap, so I
think the chance for precip in our area is low at best.  The
remainder of the short term through Sunday looks dry.  The deepening
trough to our east will suppress temperatures a few degrees, so
today will likely be the warmest day in the short term with highs
near normal in the mid to upper 80s.  Saturday and Sunday look a few
degrees cooler in the low to mid 80s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Issued at 401 AM CDT Fri Aug 21 2026

Medium range guidance suggests that the general upper pattern
will persist with the Mid Mississippi Valley in northwest flow
sandwiched between a ridge to the west and a trough to the east. A
short wave rounds the ridge Sunday and moves southeast through the
Mid Mississippi Valley and eastern Plains Sunday night into Monday.
This forces low level cyclogenesis over the Plains resulting in a
modest southwesterly low level jet nosing into Missouri Sunday night
into Monday.  Deterministic guidance keeps most of the precip out of
our area across southwest Missouri, but a small shift eastward in
the position of the low level system could push that precip farther
east into our area late Sunday night into Monday.  About 30% of the
LREF members pick up on this possibility, which makes NBM`s 30-40
PoPs late Sunday night into Monday reasonable.  With the potential
for convective debris and/or showers during the day, Monday would be
the coolest day of the week with highs only reaching the upper 70s
to low 80s. The LREF is showing some variance though with high
temperature IQRs up to 11 degrees in some locations.  Therefore
Monday`s temperature forecast could change drastically over the next
few days.

There are at least 2 more chances for rain next week as short waves
move across the area in northwest flow aloft.   The first will be
Tuesday night into Wednesday, and the second is on Friday.  Both of
these waves look like they`re at least enhanced by convection
upstream, if not convectively induced altogether.  These features
are unpredictable at best in the medium range, so confidence in the
precipitation forecasts for both days is low.  Temperatures should
warm back up to near or slightly above normal by the end of the week
as the trough over the eastern U.S. attenuates allowing the ridge to
edge eastward a bit.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1219 PM CDT Fri Aug 21 2026

For the most part, VFR conditions and light winds are expected
over the coming 24-36 hours. There is a weak cold front moving
through overnight, but it`s unlikely to produce any
thunderstorms locally and will most likely move through dry.
There could be some valley fog by morning, though confidence is
not very high on this. This would be most likely at SUS.
Otherwise winds become NNW by Saturday morning with VFR
expected.

&&

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

&&

$$

SHORT TERM...Carney
LONG TERM...Carney
AVIATION...Kimble