St. Charles, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

046
FXUS63 KLSX 112338
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
638 PM CDT Sat Apr 11 2026

.KEY MESSAGES...

- Showers and scattered thunderstorms are forecast (50-80%) for
  the area Sunday afternoon into Monday morning.

- Several chances for showers and thunderstorms will impact the
  region Tuesday through the end of the week, with potential for
  some severe thunderstorms.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 243 PM CDT Sat Apr 11 2026

Afternoon temperatures have warmed into the 70s for locations along
and south of I-70 where southerly WAA has been more prevalent, with
upper 60s to the north. Scattered showers, along with isolated weak
pop-up thunderstorms, have been slowly working northeastward across
MO. This activity is associated with a warm front that is lifting
poleward across the area today and is being driven by low-level
convergence along the front and WAA behind the front. A weakening
mesoscale convective system (MCS) exited Kansas earlier this morning
and has been moving eastward across northern MO, riding along an
obscure mid-level shortwave with an associated vort max. High-res
guidance has consistently shown a weakening trend with this system
as it outruns the core of a 30-40kt low-level jet that is across the
Central Plains. If weakening is slower than indicated by CAMs, there
is about a 50% chance the southern end of this system clips
northeast MO/west-central IL, bringing a round of more widespread
showers and thunderstorms this afternoon. Low chances (20-40%) for
scattered showers and an isolated weak thunderstorm will continue
for most of the area this afternoon/evening as the warm front
continues lifting to the north.

All of the area should remain dry tonight, aside from far northeast
MO, where a low chance (20%) for a stray shower exists. This is
closer to where the best forcing will be with areas of nebulous mid-
level energy propagating along the southwesterly flow regime to the
north/west of the area. With continued southerly WAA overnight, lows
will be much warmer than last night in the 60s for most locations.
By Sunday morning, a mid-level shortwave will be sliding
northeastward from the Plains, with high-res guidance resolving
showers and thunderstorms across KS/OK correlated with this feature.
This field of precipitation is forecast to lift northeast into the
area with chances for a round of showers and an isolated
thunderstorm increasing from southwest to northeast beginning early
Sunday afternoon. The more robust mid-level forcing stays just north
and west of the area, resulting in the greatest chances (70-80%) for
more widespread rainfall across central/northeast MO and west-
central IL Sunday evening. The 12Z HREF mean accumulated
precipitation reveals that most the area may see less than 0.05",
with a swath of >0.25" the locations mentioned above and points
northwest. Some locations, particularly across southern MO/IL, may
not receive any measurable rainfall from this round of
precipitation. Highs on Sunday will be warmer than today with
widespread temperatures in the upper 70s/lower 80s by the
afternoon.

Peine/Gosselin

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 243 PM CDT Sat Apr 11 2026

By Monday, the large-scale pattern features an amplified longwave
trough near the West Coast with a broad ridge across the eastern
United States, placing the area in strong southwesterly flow. Long-
range guidance reveals the aforementioned mid-level shortwave and
greatest forcing for ascent will be departing the area early on
Monday. Right on the heels of the shortwave, guidance unveils subtle
ridging within the southwesterly flow that will be nudging into the
area, resulting in weak height rises aloft. As a result, shower and
thunderstorm coverage should gradually fade early on Monday.
However, instability will be increasing under the southwesterly flow
regime, with LREF mean SBCAPE >1,000 J/kg across the entire area
with the greatest instability (>1,500 J/kg) expected across
central/northeast MO and west-central IL. Wind shear will also be
favorable (30kt 0-500mb Bulk Wind Shear), meaning that the
environment has potential to support stronger thunderstorm.
Although, with a lack of mid-level forcing for ascent (rising
heights aloft), the current expectation is that only a spot pop-up
thunderstorm is possible on Monday. A majority of Monday is forecast
to remain largely dry with the NBM indicating probabilities for
measurable rainfall less than 20% for the entire area Monday
afternoon into Tuesday.

Instability is progged by guidance to be greater on Tuesday,
indicated by LREF mean SBCAPE over 1,500 J/kg for most the area with
>2,000 J/kg possible across central/northeast MO and west-central
IL. The greatest mid-level forcing should still be centered north
and west of our area, out over the Plains, closer to the amplified
longwave trough that should be traversing the Intermountain West.
However, more nebulous activity out ahead of the longwave trough
within southwesterly flow aloft will lead to increasing shower and
thunderstorm potential Tuesday afternoon into Tuesday night. Bulk 0-
500mb wind shear will be slightly higher as well leading to LREF
joint probabilities of SBCAPE >1,000 J/kg and 0-500mb shear >30kts
that reach 80-90% across central/northeast MO and west-central IL.
The above features result in slightly more favorable conditions for
stronger to severe thunderstorms Tuesday afternoon into early on
Wednesday.

Model guidance has trended a bit slower with the longwave trough
ejection and is now in slightly better consensus that it should be
advancing into the Plains on Wednesday. The strongest mid-level
forcing for ascent along with the greatest deep-layer environmental
wind shear for the area will exist as this trough swings into the
Midwest, which appears to be sometime Wednesday afternoon into early
Thursday. Mean LREF 0-500mb Bulk Wind Shear reaches 40-50kts for
much of the area with mean MUCAPE around 1,000 J/kg for the whole
area. Based off this, the areas best and most widespread chance for
strong to severe thunderstorms appears to be centered on Wednesday
into Wednesday night. It is worth noting that this is still 5 days
out, meaning that timing/strength/placement of the trough ejection
will likely be fine tuned as guidance comes into better agreement.
Long-range guidance varies significantly behind the longwave trough
with general consensus being troughing out west and weak ridging to
the east, resulting in continued southwesterly flow for our area.
This means an active and warm pattern should remain in place into
next weekend as little shortwaves progress northeastward across the
area along with another potential trough ejection sometime late in
the week into next weekend. Confidence is high in temperatures 5-15
degrees warmer than average next week, as LREF temperature IQR
spread is around 3-7 degrees Monday through Friday.

Peine/Gosselin

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 638 PM CDT Sat Apr 11 2026

There is little sign of precipitation this evening as showers and
thunderstorms to the north and west have all but dissipated late
this afternoon/early evening. A few sprinkles are all that is
remnant from earlier convection. VFR conditions are expected to be
maintained over much of the area, aside from a localized, brief
dip near MVFR over the next few hours.

A disturbance attempts to bring showers and an isolated
thunderstorm to the region Sunday. However, instability is largely
lacking with little support for thunderstorms. Showers are favored
over thunderstorms until after the 24 hour period and near the end
of the KSTL 30-hour TAF. That said, convective potential remains
limited as diurnal instability becomes less prevalent. Showers
will be more isolated near metro terminals with a bit better
coverage from KCOU/KJEF through KUIN. For now, PROB30 -SHRA was
leaned on for precipitation potential. Cloud bases remain at or
above low-end VFR categories with MVFR possible at KUIN/KCOU/KJEF
late Sunday evening.

Maples

&&

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

$$

WFO LSX