838
FXUS63 KLSX 121737
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1237 PM CDT Mon Oct 12 2026

.KEY MESSAGES...

- The warmest stretch of near-record heat is expected today and
  Tuesday with highs in the low to mid-90s.

- Showers and thunderstorms arrive Tuesday night with a low
  potential for marginally severe hail and damaging winds.

- Additional rounds of widespread, beneficial rainfall are
  expected through Thursday. A cold front will bring an end to
  the active pattern with cool, dry conditions by late week into
  next weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 320 AM CDT Mon Oct 12 2026

The hottest stretch of near-record temperatures is expected today
through Tuesday. A stalling cold front will slowly approach the area
Tuesday night, bringing increasing chances for showers and
thunderstorms. Thunderstorms could produce locally heavy rain,
marginally severe hail, and damaging winds.

The Mid-Mississippi Valley will be positioned under the northern
reaches of an upper level ridge today through Tuesday. Surface to
mid-level ridging stretches from the northern Gulf through the Mid-
Atlantic Region, resulting in southwesterly low level flow. RAP
guidance shows strong warm air advection progressing generally west
to east this morning with mid-level temperatures rising from the
mid/upper teens (C) to around 20C by Tuesday afternoon. This
morning`s (08z) surface temperatures are in the 60s over IL and
warm to the mid-70s over western MO. IR satellite shows
scattered/broken upper level cloud cover that is expected to
clear by mid-morning. Clearing will allow for deep mixing with
little sign of a lingering cap. Dewpoints in the mid-50s to
low-60s will allow for temperatures to reach near records again
today with highs largely in the 90s. The difference Tuesday will
be the subtle increase in mid-level temperatures and moisture
with dewpoints in the upper 60s to low- 70s. It`ll feel more
like mid-summer than October, registering heat index values
through the afternoon. Peak heat heat indices could reach
100-105 degrees along the MO River Valley into SW IL.

Fortunately, the most uncomfortable heat will not last long. A weak
shortwave and corresponding surface low tracks through the northern
Plains into the Great Lakes, dragging a slow-moving cold front in
from the northwest. This front briefly stalls, more so becoming
quasi-stationary as an large upper low hangs out over the Rockies.
Boundary layer moisture pools along and ahead of the front, where
dewpoints climb into the 70s and PWATs increase above 1.75 inches.
Thunderstorms initiate over the easter Plains Tuesday afternoon,
riding along and north of the boundary, as a piece of upper
vorticity/shortwave ejects out ahead of the parent upper low. This
will enhance ascent over the boundary from northwest MO through
southern IA, then gradually sink southward late Tuesday evening into
the overnight period. Though 500mb winds are around the 95th
climatological percentiles and HREF probabilistic CAPE values show
1300-2000 (25th/75th percentiles) in the warm sector, mid-level
lapse rates of 6.0-6.5C are fairly modest. Additionally, their
arrival could be well after peak maturity, when outflow dominates, a
cap develops (elevated thunderstorms) and heavy rain becomes the
dominating feature. Therefore, while there is some support for
marginally severe hail/damaging winds, the potential is low,
isolated, and likely confined to northeast reaches of the CWA
(NE MO) and possibly as far south as central MO. With PWATs
nearing 2 inches, locally heavy rain is possible with localized
rainfall rates of 1-2 in./hr.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 320 AM CDT Mon Oct 12 2026

Widespread showers and embedded thunderstorms will continue to
slowly drift southward through the area Wednesday. Ample cloud cover
and rain-cooled air should help limit much reinvigoration of the
surface based convection, at least along and north of I-70. The
leading shortwave exits to the east with a lull in precipitation
coverage and intensity, though isolated to scattered showers cannot
be ruled out along the stalled boundary.

A second shortwave ejects eastward from the broad upper low and
produces yet another round of thunderstorms over eastern KS into
western MO late Wednesday. This moves almost due west to east
Wednesday evening into Wednesday night as the cooler air
reinforces the boundary slightly southward. The upside is that
the position of the boundary is slightly south of the highest
rain potential from Tuesday night, running roughly along and
south of I-70. Along with the subtle southward shift in the
surface boundary and the quick movement of the shortwave within
the strong 500mb flow, heavy rain should not sit over one
particular area very long, though bouts of heavy rain will
occasionally pass through with embedded thunderstorms. Rainfall
and cloud cover will keep temperatures 10-15 degrees cooler than
the record-level territory achieved Monday and Tuesday. That
said, it`s still impressive to be in mid-October and reach the
low-80s with cloud cover and rainfall.

Long range guidance (ECM/GFS) remain far departed in the handling of
the upper level pattern Thursday into Friday. However, the dominate
surface feature is a strong surface high that builds into the Plains
as a separate long wave trough drops southeast through the
Great Lakes. The two, in tandem, will help clear the frontal
boundary to the south of the area, bringing cooler, drier air to
the region. The center of the ridge and eastward movement
varies slightly between guidance. That said, it does look to be
positioned overhead Saturday morning, and possibly into Sunday
morning. Clear skies and light surface wind could bring the
coolest temperatures of the season dipping below normal, for a
change. LREF probabilistic (25th/75th percentiles) guidance
shows less spread (5-7 degrees) in Saturday morning lows,
ranging from the mid-30s to low-40s. Sunday morning`s spread
increases slightly with the ECM pulling the surface high
eastward a little quicker, though Sunday morning lows range from
the mid-30s to mid-40s between the IQR. If narrows in on this
solution, it could be the first decent chance at frost this
fall.

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1236 PM CDT Mon Oct 12 2026

Dry and VFR flight conditions are likely to persist through the TAF
period. Southwesterly winds will slacken and back toward southerly
around sunset with gusts diminishing. Through Tuesday morning, winds
will veer back toward southwesterly. A cold front will arrive and
stall in the vicinity of KUIN Tuesday morning as well, which could
veer winds further to the northwest, but the exact position of this
front is uncertain.

&&

.CLIMATE...
Issued at 624 AM CDT Mon Oct 12 2026

CORRECTED FOR FORMATTING
Issued at 257 AM CDT Sun Oct 11 2026

Very warm temperatures are expected over the next several days.
This will challenge daily record highs and record warm lows on
multiple occasions. The daily records threatened are shown
below.

Record High Temperatures:

October 12:
KSTL: 89/1890
KCOU: 94/1899
KUIN: 90/2024

October 13:
KSTL: 90/1899
KCOU: 95/1899
KUIN: 87/1975

Record High Minimum Temperatures:

October 12:
KSTL: 70/1997
KCOU: 69/1928
KUIN: 70/1928

October 13:
KSTL: 69/2008
KCOU: 69/1899
KUIN: 65/1935

October 14:
KSTL: 70/1899
KCOU: 67/2017
KUIN: 67/1920

In addition, all time monthly record high temperatures are
within range of being broken. The following are the October
monthly high temperature records at each site:

October Record High:
KSTL: 94 most recently on Oct 1, 2019
KCOU: 96 on Oct 7, 1939
KUIN: 96 on Oct 7, 1939

&&

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

&&

$$

SHORT TERM...Maples
LONG TERM...Maples
AVIATION...Pfahler
CLIMATE...Maples