St. Peters, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

659
FXUS63 KLSX 090836
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
336 AM CDT Mon Jun 9 2025

.KEY MESSAGES...

- Outside of a 20% chance for showers this afternoon along/south
  of I-44, dry and tranquil conditions will prevail through
  Wednesday. The reprieve ends late Thursday with a return to
  showery, more unsettled weather.

- St. Louis` unusual stretch without warming to 90 degrees this
  year is in jeopardy a few times this week as more summerlike
  warmth builds.

&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 334 AM CDT Mon Jun 9 2025

The cold front that initiated showers and thunderstorms, a few
of which became severe, is moving through the Missouri Bootheel
this morning per regional surface observations and will soon exit
the region altogether. In its wake, slightly cooler and drier air
is settling across the Mid-Mississippi Valley. Another reinforcing
cold front is also evident in surface observations tied to
stronger cyclonic flow aloft in the Upper Midwest. The front will
cross through the bi-state region through the day, with
temperatures behind it warming to the mid/upper 70s (5-10 degrees
below normal). Ahead of it, the warm and drier boundary layer
amidst stronger southwest winds will promote steep (7-8C/km) 0-3km
lapse rates and increased SBCAPE per high-resolution guidance.
With modest but present low-level convergence and the
aforementioned thermodynamic environment, there`s a 20% chance for
weak showers generally along and south of the I-44 corridor in
Missouri and I-55 in Illinois during the afternoon and early
evening. Model soundings show mid- level warming and subsidence
above the low-level convergence, likely quashing any threat for
thunderstorms.

The front exits the region during the early evening, with calmer
winds and a surface high settling in overnight. Winds gradually
strengthen and become westerly through the day Tuesday with the high
shifting south and east of the forecast area. The westerly winds
will keep surface moisture in check and highs seasonable (low 80s).
The flow continues to back through the afternoon, eventually leading
to an uptick in warm air advection that sets the stage for more
summerlike conditions mid-week.

MRB

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 334 AM CDT Mon Jun 9 2025

Broad upper-level ridging and a more amplified warm air advection
regime encompasses the central CONUS by Wednesday, sending
temperatures several degrees warmer than Tuesday`s highs and drawing
Gulf moisture poleward into the region amidst stronger southerly
winds. As is noted in the Climate section of this forecast
discussion, St. Louis has not officially observed a daily maximum
temperature of 90 degrees this year, which is fairly unusual in the
period of record. With neither today nor Tuesday reasonably expected
to reach 90 degrees, this will be the first time in 30 years St.
Louis hasn`t hit this mark by June 10th. This unusual stretch will
be threatened both Wednesday and Thursday, with both the official
high temperature forecast and the NBM maximum temperature IQR
hovering around the 90 degree mark. The best chance for this streak
to end is Wednesday, as cloud cover will be fairly minimal.

High cirrus and eventually mid-level clouds will gradually stream
in overnight into Thursday with the approach of a cutoff upper-
level low that`s evident in most global ensembles and
deterministic guidance. While the WAA regime is still in place,
the combination of more abundant cloud cover and increased (albeit
low) rain chances with the upper-level wave throws increased
uncertainty into how warm we will get. That said, rain chances are
being delayed with every run of guidance, and it may be that we
make another run at upper 80s to 90 degrees on Thursday.

The real thrust of the synoptic ascent and moisture arrive Friday,
leading to showers and a few rumbles of thunder across the region.
Temperatures are a bit more uncertain at this point as some
ensemble members eject the upper-level wave quickly while others
stall it overhead all day on Friday. Regardless, the IQR for high
temperatures is at least around the normal mid-80s we`d expect for
mid-June. Regardless of how this initial wave of rain evolves,
this appears to usher in another period of unsettled weather
marked by persistent chances for showers and a few thunderstorms
through the weekend. Nothing appears particularly hazardous or
severe at the moment, with CIPS Severe Probability Guidance from
Saint Louis University and Colorado State University Machine
Learning guidance keeping even low threats for severe weather
clear of the forecast area.

MRB

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1032 PM CDT Sun Jun 8 2025

Showers are expected to move out of the terminals by 06Z.
Otherwise dry and VFR conditions are expected the rest of the
period with skies clearing by tomorrow morning. Winds will pick up
out of the west to northwest (260 to 280 degrees) with gusts to 20
knots during the day on Monday before turning light after 00Z on
Monday evening.

Britt

&&

.CLIMATE...
Issued at 227 PM CDT Fri Jun 6 2025

St Louis has still not seen 90 degrees yet in 2025. The average
first 90 degree reading is May 20. The most recent late 90-degree
start was June 10, 2021. If St Louis doesn`t hit 90 by June 10,
it will be the latest first 90 degree day since at least 1995
(June 19). The latest date of first 90 degrees on record was July
4 in both 1961 and 1912.

Columbia has also not yet seen a 90 degree reading in 2025, however
the average first date is much later (May 31). The latest date of
first 90 degrees on record was July 14, 1904.

Quincy reached 90 degrees on May 15 of this year, about 3 weeks
earlier than their average first 90 degrees (June 2).

Kimble


&&

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

$$

WFO LSX