Area Forecast Discussion

910
FXUS63 KLSX 230812
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
312 AM CDT Mon Mar 23 2026

.KEY MESSAGES...

- Temperatures will warm back to above average this week with
  Thursday being the warmest day, featuring near-record high
  temperatures.

- A cold front Thursday night into Friday will provide an
  opportunity for showers and thunderstorms along with a possible
  freeze Friday night/Saturday morning.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 311 AM CDT Mon Mar 23 2026

Behind Sunday`s cold front, strong low-level CAA continues to
promote significant cooling of temperatures this morning toward the
30s F, around 40 to 50 F cooler than Sunday afternoon`s
temperatures. CAA will very gradually weaken today as a surface
anticyclone passes to the north of the CWA. In this newly
established, seasonably cool airmass, high temperatures will reach
the 50s F--slightly below average. This airmass will also be rather
dry with low RH this afternoon, but it is uncertain if winds will
remain strong enough for Elevated Fire Danger, since vegetation
remains very dry and is still exiting dormancy. That being said,
sporadic Elevated Fire Danger is possible across southeastern
MO/southwestern IL, further away from the anticyclone with slightly
stronger winds. Clouds will also be increasing this afternoon in
advance of an upper-level shortwave trough traversing the Mid-
Mississippi River Valley tonight within northwesterly flow. With the
dry low-level airmass and ascent largely in upper/mid levels, mainly
virga (precipitation evaporating before reaching the ground) is
expected tonight, but there could be a few sprinkles at the surface
where there is some transient low-level FGEN.

As the surface anticyclone shifts further to the northeast on
Tuesday, low-level flow will become increasingly southerly with WAA
ensuing. Therefore, warmer and slightly above average high
temperatures in the upper 50s to mid-60s F are expected on Tuesday
with some insolation between bouts of upper and mid-level clouds.

Pfahler

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 311 AM CDT Mon Mar 23 2026

The aforementioned warming trend will continue through Wednesday and
Thursday with temperatures returning to well-above average as a warm
front lifts northeastward across the CWA on Wednesday. Considering
some variability in the position of the front on Wednesday there is
slightly lower confidence in high temperatures that day with the NBM
interquartile range around 10 F, from near 70 to around 80 F. Around
10 to 30 percent of ensemble model membership has showers and a few
thunderstorms developing Wednesday night/Thursday morning in south-
central/southwestern IL as a LLJ interacts with the warm front, but
higher probabilities of measurable rainfall are further east of the
CWA which is more favorably positioned relative to warm front
placement. With the CWA firmly in the warm sector on Thursday,
confidence is high that Thursday will be the warmest day of the week
as 850-hPa temperatures near seasonal record maximums with
ingredients there for values to break daily records and even
threaten all-time March records. As such, the NBM has probabilities
of high temperatures in the 90s F at 40 to 70 percent along/south of
I-70 in MO.

Analog and machine learning guidance continue to indicate that the
threat of severe weather will need to be monitored on Thursday with
many pieces of model guidance showing an overlap of instability and
wind shear. That being said, there are still complicating factors
present for the CWA including a potential capping inversion across
the unstable warm sector and, if there is surface-based initiation
along an incoming cold front Thursday evening, the largely west-to-
east orientation of the front can sometimes cause thunderstorms to
be undercut, making it harder for them to be severe. The majority of
ensemble model membership does not actually have precipitation until
Thursday night into Friday, largely behind the southward-moving
front as an upper-level trough tracks across the Midwest and Great
Lakes. With the cooler airmass behind the front and lingering clouds
and precipitation on Friday, another large drop in temperatures from
well-above average on Thursday to below average is expected again,
similar to that of the last 24 hours. NBM probabilities of low
temperatures below 32 F are also 30 to 70 percent for much of the
CWA Saturday morning, which threatens any seasonal vegetation that
may become susceptible by that point. However, a return to low-level
southerly flow is generally agreed upon by model guidance,
permitting a warming trend of temperatures back to above average by
Sunday.

Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1031 PM CDT Sun Mar 22 2026

Dry and VFR conditions will prevail through the TAF period, with
winds gradually weakening overnight out of the north. A brief
period of MVFR CIGs may develop at KUIN, but the upstream clouds
are beginning to dissipate so no CIG was included in the TAF.

Winds gradually turn out of the east with time through the
afternoon tomorrow, and remain near 10kts through the rest of the
period.

MRB

&&

.CLIMATE...
Issued at 136 PM CDT Sun Mar 22 2026

Record High at STL for 3/22
       STL
3/22 88 (1907)

Record Highs on March 26:
St Louis   87 in 1991
Columbia   86 in 1910
Quincy     82 in 1991

All Time March High Temperature Record:
St Louis   92 on March 24, 1929
Columbia   92 on March 21, 1907
Quincy     88 on March 21, 1907


&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion