398
FXUS63 KLSX 182106
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
306 PM CST Tue Nov 18 2025

.KEY MESSAGES...

- Isolated thunderstorms are possible (25% chance) in southern MO
  and IL through 6pm. If these storms develop, they may quickly
  become severe before moving out of the forecast area, with all
  hazards possible.

- Widespread rainfall is expected from late Wednesday through late
  Friday.

&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 300 PM CST Tue Nov 18 2025

As of this writing (3pm), a shortwave is zipping through the
Midwest, with an associated surface low over eastern Missouri. As
a result, the southern 1/2 of the CWA is in the warm sector of
the low and is a rough approximation of where there is sufficient
moisture and instability to support thunderstorms this afternoon.
We also need some lift to see thunderstorms develop, and while
we`ll see some mid-level lift over the region on the southern
flank of the above shortwave, we`ll also need some assistance from
the cold front to initiate thunderstorms in the mid-MS Valley.

The front, currently extending from just south of St. Louis
south-southwestward toward Springfield, MO, is expected to slide
quickly eastward through the afternoon. However, winds in the warm
sector are largely parallel to the front, limiting convergence
and lift. As such, the vast majority of high res model guidance
shows at most isolated thunderstorm coverage in our forecast area
before storms become more widespread in southern IL. Further,
there are several models that don`t develop storms in our CWA at
all and that`s a real possibility for us.

All that being said, we have seen a few showers develop in
southern MO away from the front, so there may be just enough lift
to support an isolated storm. Given ample deep and low level wind
shear, ~50 and 20kts, respectively), if a thunderstorm is able to
develop (~20% chance) it may quickly become severe before moving
out of the forecast area, with all hazards possible.

Tomorrow, mid level flow will become more zonal in the wake of the
above shortwave with west/northwesterly low level winds pulling
cooler temperatures in the region. There is a bit of disagreement on
the degree of cloud coverage, and therefore temperatures, we`ll
see tomorrow, but it will almost certainly be cooler than today.

BSH

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 300 PM CST Tue Nov 18 2025

By Thursday morning, we`ll begin seeing height falls as a deep
shortwave ejects out of the desert southwest. In response, gradual
cyclogenesis will take place over the Plains, shoving the remnants
of today`s front back north into the area and ushering deeper
moisture back into the mid-MS Valley. The vast majority of guidance
has precipitation beginning on Thursday morning over the southern
forecast are as that warm and moist advection interacts with the
front. Rain will persist on and off through the day on Thursday
before moving north on Friday as that southerly low level flow
slowly shunts the front north and the shortwave moves into
through the region. As a result, we should see a needed soaking
rain, with LREF probabilities of at least 1" of rain > 75% along
and south of I- 70. Rainfall amounts are expected to be less
further north, but even areas along the MO/IA border have at least
a 50% chance of seeing > 0.5" of rain, per the HREF.

By the weekend, we`re expected to return to generally zonal flow as
we wait for a cut-off low to slowly eject out of the desert
southwest. The arrival of this cutoff low will represent our next
chance of rain after Friday, though there is some disagreement on
when exactly that will occur. Fortunately it appears the earliest
more rain would arrive is early in the workweek.

One point worth noting is that there is no real surge of cold air
associated with any of the rounds of rain in this forecast. As a
result, temperatures are generally expected to remain above
normal throughout the forecast period.

BSH

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1127 AM CST Tue Nov 18 2025

Areas of broken stratus are accompanying a slow-moving frontal
system this afternoon. Ceilings have generally oscillated between
MVFR and VFR; however, upstream observations support the stratus
scattering out for a brief time, namely between 21z-03z. It is
after that time that an area of low stratus will creep into the
regional terminals from the north. Confidence is reasonably high
(greater than 70% chance) that MVFR ceilings will return by 06z,
if not shortly before such time. There is even some potential for
IFR ceilings to develop between 09z-12z, but confidence is not
high enough to introduce it as the dominant category. Low ceilings
(MVFR/IFR) will then persist through the remainder of this TAF
cycle.

SPECIFICS FOR KSTL:

There is a low probability (less than 30% chance) for scattered
thunderstorms to develop early on in the TAF period, particularly
between 18z-20z, as a cold front slumps into the regional
terminals. Confidence and coverage are both too low to include in
the TAF at this time.

WFO LSX

&&

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

$$

WFO LSX