St. Peters, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

087
FXUS63 KLSX 242313
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
613 PM CDT Thu Apr 24 2025

.KEY MESSAGES...

- The threat of showers and thunderstorms will increase across the
  area tonight, peaking later this evening through Friday (50-60%
  chance).

- A brief return of cooler temperatures will occur on Saturday
  followed by a big warm-up into early next week with well above
  normal readings on Monday.

- Thunderstorm chances will ramp-up again late Monday and there is
  an increasing chance of strong to severe storms late Monday
  night and Tuesday.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 236 PM CDT Thu Apr 24 2025

A series of low amplitude disturbances will move across the region
later tonight and Friday as the associated short wave trof traverses
the area. While the threat/coverage of precipitation is expected to
increase area-wide tonight, there is quite a bit of variance in
convective evolution and coverage with the CAMS. The most consistent
and best signal indicates the combination of large scale ascent with
the aforementioned disturbance and moisture convergence associated
with a veering southwesterly LLJ will promote showers and
thunderstorms across central and northeast MO into west-central
IL later this evening into the overnight hours. Outside of this
region, present indications are coverage would be lesser and more
scattered owing to diminished forcing.

The convective coverage and evolution is even more murky on Friday.
Despite another disturbance tracking across the area, the
attendant forcing is very weak at best and the region is actually
in large scale subsidence by afternoon. Thus the advancing cold
front and any pre-frontal boundaries will be the primary catalyst
for showers and storms. As stated yesterday, the warm sector
instability will be impacted by clouds and ongoing precipitation
and the consensus is 500-1000+ J/KG MLCAPE will be present with
deep layer shear of 20-25 kts. These values along with the nature
of the forcing would support isolated to scattered coverage
(possibly clusters or short segments of multicell storms) into
early afternoon with coverage trending towards more isolated in
the afternoon and early evening. While the threat of severe is not
zero it remains quite low at this time and would be where
instability is locally maximized.

Glass

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 236 PM CDT Thu Apr 24 2025

Confidence is high that the one totally dry day will be Saturday
with northwest flow aloft and expansive post-frontal surface high
pressure centered through the Great Lakes dominating the sensible
weather. This combination along with the expectation there will be
quite a bit of cloudiness will result in high temperatures that
will be near to slightly below normal.

A notable pattern change is still forecast to take place beginning
late Saturday into Sunday as a deep upper trof/low moves through the
western U.S. and an upper ridge builds and shifts from the Plains
into the Mississippi Valley. In conjunction with this change,
return flow and a warm advection regime will evolve Sunday into
Sunday night. There are some questions whether we will see any
precipitation on Sunday with some guidance showing an impulse
moving through the building ridge and the return flow to the west
possibly supporting showers into central and southeast MO.
Otherwise clouds will also be more prevalent and they could impact
the magnitude of warmer temperatures on Sunday.

There is now relatively good consensus the western U.S. upper
trof/low will weaken/deamplify as it lifts northeastward through the
central/northern Plains on Monday and into and through the Upper
Mississippi Valley late Monday night/early Tuesday. This progression
will bring increasing southwest flow aloft on Monday and strong low-
level WAA resulting in well above normal high temperatures. Presently
it appears that warm sector cloudiness could limit just how warm
wet get, however if cloudiness is less extensive, then the 75th
percentile of the NBM probabilistic temperature guidance would
have highs in record territory.

We are still actively watching the period from late Monday night
into Tuesday for the possibility of strong to severe storms. Any
threat late Monday night would appear to be confined to NE MO
associated with storms moving into that area from the west/northwest
ahead of the advancing cold front. At this time there is concern of
a capping inversion inhibiting storms rooted in the boundary layer.
However on Tuesday into Tuesday evening the cold front should
progress across the CWA, and the combo of heating and cooling
aloft associated with mid-level perturbations in the southwest
flow aloft should result in an uncapped air mass by afternoon, and
development of thunderstorms spanning the frontal zone. The LREF
along with deterministic models continue to show at least 40-45
kts of deep layer shear, steep mid-level lapse rates and at least
1000-1500+ J/KG of SBCAPE (this is likely conservative). That
shear/instability combination is favorable for organized severe
thunderstorms which continue to be highlighted in the machine
learning guidance and the SPC DY6 Outlook. Given this is still
pretty far out in the forecast package, we are easing into
mentioning the severe potential. If nothing changes we will begin
to ramp-up our messaging on Friday.

The pattern will remain active into late week with the ensembles
showing another southern stream upper trof impacting the area in the
late Wednesday-Thursday time frame bringing additional chances of
showers and thunderstorms.

Well folks this marks the final operational forecast shift and AFD
of my 41+ year NWS career with my retirement slated for April 30th.
A "back of the envelope" calculation would estimate I`ve written
3000+ AFDs and SFDs (State Forecast Discussion) in my 35 years at
NWS St. Louis. It has been an extremely rewarding and fulfilling
career that I probably couldn`t have scripted any better. I`ve been
privileged with excellent mentors and I`ve embraced the role of a
mentor passing on my years of experience and knowledge. Without a
doubt the most memorable event in my career was my role as the
warning forecaster for the Good Friday Tornadoes on April 22, 2011.
It is also one of many other memorable severe and winter winter
events that include the Great Flood of 1993. I estimate I`ve
probably issued around 300 tornado warnings, 1200-1500 severe
thunderstorm warnings, and 150 or so flash flood warnings over the
years. The amount of change over the years has been immense.
Significant changes lie ahead for the NWS, and you will not find a
finer, more dedicated workforce that is committed to excellence and
conquering the challenges that lie ahead. It has been an honor to
serve the residents across central and eastern Missouri and western
Illinois. Lastly, I will greatly miss the people: my friends and co-
workers at NWS LSX, many other NWS and NOAA meteorologists that I
have coordinated and collaborated with, our engaging core partners,
and especially our local media partners! My passion for weather
remains strong, and although I`m retiring, I am not disappearing.
See you on the flip side.

Glass

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 607 PM CDT Thu Apr 24 2025

Scattered thunderstorms may impact central Missouri sites and/or
KUIN late this evening/early overnight ahead of an approaching
cold front. This front will move through the area on Friday, with
metro terminals having the best chance of seeing scattered storms
early Friday afternoon. Thunderstorms should be pretty weak, but
brief reductions in visibilities are the main threat with any
downpours. Behind the front, dry weather with a wind shift to the
northwest is forecast. There also may be some MVFR ceilings at
KCOU/KJEF/KUIN behind the front, but the signal is mixed so just
added a SCT025 group for now.

Gosselin

&&

.CLIMATE...
Issued at 218 AM CDT Wed Apr 23 2025

Unseasonably warm temperatures are expected on Monday, nearing
daily records for late April. Here are the daily record highs
for April 28.

LOCATION        RECORD
ST LOUIS    92 set in 1970
COLUMBIA    88 set in 1970
QUINCY      88 set in 1970


&&

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

$$

WFO LSX