284
FXUS63 KLSX 252310
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
610 PM CDT Fri Sep 25 2026

.KEY MESSAGES...

- Seasonably cool and cloudy weather is expected to continue
  into the weekend, with the coolest conditions for those who
  see rain.

- The best rain chances (60-80%) are across northeast MO/west-
  central IL this weekend. More widespread and significant
  (0.50+ inches) rainfall is expected next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 236 PM CDT Fri Sep 25 2026

Mid-level ridging is located across the center of the country with
longwave troughing on either side. The northern periphery of this
ridge is across the Midwest with vorticity lobes pivoting around the
top of this ridge into Iowa and northern MO. This is where a region
of showers have been ongoing today with light rain intermittently
impacting locations across central/northeast MO and west-central IL.
These showers have been fighting low-level dry air that is in place
to the east across the rest of the area and have yet to make it into
east-central MO or locations further east. Low-level cloud cover has
been less prevalent today compared to yesterday. However, mid-level
clouds have been more abundant as upstream mid-level moisture pivots
into the area. Areawide temperatures range from the mid 60s to low
70s this afternoon with highs expected to reach the low/mid 70s for
most locations. Areas that remain mostly cloudy tonight will stay
warmer with lows in the 60s, while areas that clear will lower into
the 50s, thanks to light surface winds leading to efficient
radiational cooling.

As we move into tomorrow, the mid-level ridge across the area
weakens slightly allowing vorticity lobes aloft to slide further
south into the area. As a result, chances for showers are higher
tomorrow, but mostly limited to northeast MO and west-central IL
where the highest chances (60-70%) are located. Low-level dry air to
the east will limit the eastward extent of showers with the LREF and
NBM showing less than a 20% chance for light rain showers to the
south of I-70 in MO and IL. Temperatures will vary by 10-15 degrees
across the area tomorrow, with a north-south gradient. Locations
where rain showers and cloud cover is more prevalent (northern
locations) should only reach the mid/upper 60s. While on the inverse
side of this, locations that stay dry and have less cloud cover
(southern locations) are forecast to reach the mid/upper 70s by
Saturday afternoon. The greatest instability stays across the Great
Plains through Saturday with the LREF showing less than 200 J/kg
MUCAPE across the entire area. The best chance (only 10%) for a weak
thunderstorm in the area is across central/northeast MO on Saturday
when MUCAPE values near 200 J/kg in the afternoon. This will mostly
be a light rain with HREF probabilities for 6hr rainfall >0.25" only
up to 50% in a few northern locations.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 236 PM CDT Fri Sep 25 2026

Not much changes by the time we get to Sunday with just a gradual
weakening of the mid-level ridge forecast to continue. This will
steadily shift the focus area of the more widespread showers from IA
into western MO. Similar to Friday and Saturday, low-level dry air
will keep these showers mostly across central MO, with some isolated
light showers making it into eastern MO and IL. Instability slightly
increases across central MO with 50% probabilities for MUCAPE >200
J/kg by Sunday afternoon according to the LREF. By Monday and
Tuesday, a longwave trough will be traversing into the Desert
Southwest, working to place the region into southwesterly flow.
Guidance has trended considerably slower with the evolution of this
feature, more than likely due to model consensus indicating a more
amplified trough now with a closed mid-level low. Now, the general
consensus reveals it entering the Great Plains Wednesday into
Thursday, about 12+ hours slower. Moisture and temperature advection
ahead of this system should aid in steadily increasing highs next
week along with increasing chances for a more widespread and
potentially substantial rainfall. Probabilities for 24hr
precipitation >0.50" on the LREF have slightly lowered, but are
still around 30-40% for portions of the area. Currently, it appears
the best chances for showers and thunderstorms will be Wednesday
into Thursday, but with a closed low at play, additional changes in
the timing are almost a guarantee. LREF temperature IQRs remain
around 5-10 degree spreads next week, centered on values slightly
above normal. By late next week into the weekend, IQR spread
increases, indicating more variance in guidance along with a
potential cold front behind the longwave trough next week.

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 606 PM CDT Fri Sep 25 2026

VFR conditions are expected to prevail through the 06Z TAF
period, with only a few low-probability exceptions. At St. Louis
area terminals (STL/SUS/CPS), some lingering stratocumulus and
cumulus clouds continue to straddle the MVFR/VFR threshold, but
remain slightly above VFR levels as of 23Z. While this is likely
to continue, there is a low chance for a brief dip to MVFR
before these lower clouds diminish later in the evening.

From here, the focus turns to rain chances, which are generally
low. Some light rain will be possible Saturday morning at
UIN/COU/JEF, but confidence is somewhat low, and we have thus
maintained a PROB30 in the TAF. St. Louis area terminals may see
a few very light showers, but confidence in visibility or
ceiling reductions is much too low to include this in the TAF.

&&

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

&&

$$

SHORT TERM...Peine
LONG TERM...Peine
AVIATION...19