Hidden Valley

000
FXUS63 KLSX 221801
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
101 PM CDT Sat Aug 22 2026

.KEY MESSAGES...

- Temperatures will be near or a few degrees below normal in the
  low to mid 80s this weekend, with relatively low humidity.

- Temperatures warm back up to the mid to upper 80s by midweek
  with slight chances for showers and thunderstorms.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 254 AM CDT Sat Aug 22 2026

The Mid Mississippi Valley remains locked in northwest flow aloft 
with an amplified upper level ridge centered near the Four Corners 
Region, and a long wave trough digging through the Ohio Valley into 
the Southeastern U.S.  A subtle short wave embedded in the northwest 
flow aloft is pushing a weak cold front south through Missouri and 
Illinois this morning.  A line of thunderstorms is moving south 
through central Illinois along or just ahead of the front.  Expect 
these storms to continue moving south and out of our forecast area 
by 09-10Z.  Temperatures behind the front will be 2 or 3 degrees 
cooler today in the mid 80s, and dew point temperatures will be 5+ 
degrees lower in most locations.  High pressure drops into the 
Mississippi Valley behind the front with light winds and a clear sky 
overnight tonight.   These excellent radiational cooling conditions 
along with the drier air behind the front will allow overnight lows 
to drop into the low 60s in most locations by Sunday morning.  The 
urban heat island of St. Louis will hang on to a little more warmth, 
but temperatures should still drop into the mid 60s which will be 
the coolest lows since the beginning of August.  The cool start to 
the day will be followed up by a cooler Sunday under the high 
pressure with highs in the low to mid 80s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 254 AM CDT Sat Aug 22 2026

The overall weather pattern persists through next week with a ridge 
to the west and a trough to the east and northwest flow aloft over 
the Mississippi Valley.  The long wave trough does attenuate 
somewhat in the Monday-Tuesday timeframe.  This allows the ridge to 
to drift eastward which brings warmer temperatures and higher 
humidity back to the region.  This doesn't look like extreme heat, 
just more "normal" late August heat and humidity.  After another 
cool start to the day Monday, and highs in the low 80s, temperatures 
rise back into the mid and upper 80s through at least Wednesday or 
Thursday. Deterministic guidance shows another short wave diving 
southwest from south central Canada into the Great Lakes region late 
in the week.  This pushes another cold front through the Mid 
Mississippi Valley with the potential for some precip and perhaps 
cooler temperatures for Friday.  However, the LREF cluster analysis 
is showing variance in both the amplitude and speed of the late-week 
short wave.  The timing and strength of the cold front along with 
the chance for precip that it brings is therefore questionable. Have 
left NBM temps and PoPs alone for the end of the week, which keeps 
highs in the mid to upper 80s and only sporadic slight chance PoPs.

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 100 PM CDT Sat Aug 22 2026

VFR conditions continue at all sites. Light winds tonight could
bring some valley fog, but this is less likely due to drier air
moving into the region today.

&&

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

&&

$$

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