727
FXUS63 KLSX 111952
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
252 PM CDT Wed Mar 11 2026

.KEY MESSAGES...

- Seasonably mild and dry weather is expected for the rest of this
  week.

- A strong cold front on Sunday brings another chance for
  thunderstorms and a sharp drop in temperature back toward wintry
  cold.

&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 251 PM CDT Wed Mar 11 2026

This morning`s cold front has brought an end to our record warm,
muggy weather and is ushering in much cooler conditions on gusty
northwest winds this afternoon. These winds will die down overnight
and clouds disperse allowing temperatures area wide to fall to near
or below freezing for the first time in about a week and a half for
most of us. Despite plenty of sun and winds turning southwesterly on
Thursday, we only warm up into the 50s. That`s right about normal
for mid March, but it will be some 25-30 degrees colder than
yesterday.

Kimble

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 251 PM CDT Wed Mar 11 2026

Late Thursday into Friday, a trough tracks east across the Upper
Midwest moving into the Great Lakes Friday morning. The bulk of the
precipitation with this trough will be closer to the track of the
Upper Low through the Great Lakes, and it`s cold enough for snow up
there. For our area, though, our brief warm up on southwesterly flow
comes to an end as a cold front trailing from behind this system
shifts winds back to the north briefly. Southern areas will be
warmer than northern areas on Friday as the front arrives quicker up
north. All uncertainty on highs Friday (NBM IQR of about 6 degrees)
relates to the timing of the front. We`re confident it will be a dry
frontal passage for our area. Today`s cold front shuts off access to
Gulf moisture for a while, so this front arriving so quickly on its
heals won`t have enough time to pull Gulf moisture northward ahead
of it.

The cool air behind this front is not very intense and doesn`t last
long at all. By Saturday zonal flow aloft across the Rockies and
Plains will already begin to initiate return southerly flow over the
Southern Plains and Mississippi Valley, pushing the front back north
as a warm front. How quickly that warm front lifts north will play a
big role in temperatures on Saturday. Clouds along and north of the
front keep things cooler, in the 40s, but once the front lifts north
and the sun comes out temperatures soar through the 60s to near 70.
So there`s considerably more uncertainty on high temperatures
Saturday, with NBM IQR as high as 10 degrees in spots. Northern
areas are likely to stay in the cool, cloudy weather longer while
southern locales are more likely to see the front lift north and
feel the full warmth of the day.

The next trough makes its way onshore in the Pacific Northwest
Friday and across the Northern Rockies on Saturday. It then digs a
broader trough over the Plains on Saturday as the core of the low
moves east into the Great Lakes. This time there`s more time for the
Gulf moisture to recharge ahead of it, developing a broad moist
sector. While confidence is high that the surface low tracks to our
north, keeping the bulk of the synoptic scale precipitation (wintry)
to our north, there is the potential for instability in the moist
sector to produce thunderstorms in the vicinity of the advancing
cold front. At the moment, guidance is indicating dewpoints rising
into the 50s with weak instability developing (less than 10 percent
of GEFS members produce 500 CAPE). For comparison, ahead of
yesterdays front dewpoints were in the mid 60s with well over 2000
CAPE. Considering how strong this system is and the wind field
associated with it, we can`t rule out a severe weather potential
developing. But the more limited moisture available is what keeps
our expectations low at this time.

Behind the front Sunday, temperatures take another tumble. This time
we have access to some truly winter-like temperatures. In fact,
there`s potential for some of the synoptically driven precipitation
wrapping around the back side of the low to bring a period of snow
Sunday night as the system exits. It`s clear that the primary area
under threat for significant snowfall is to the north across Iowa
into the Great Lakes, but depending on how the system evolves there
could be a brief period of snow down here as well. Currently about
20 to 50 percent of low resolution ensemble guidance produces snow
across our region, roughly on par with recent model runs. However,
less than 15 percent of members produce enough snow to pose a threat
for ground accumulation (0.1 liquid equivalent falling as snow).

The surface high associated with this cold air mass plunges straight
south through the Plains, with the core of the cold air pushing
through the central US and into our area early next week. While
there is the usual amount of uncertainty on just how cold it will be
5 to 6 days out (NBM IQR of 8 to 10 degrees), we are quite confident
that it will be cold. In fact, almost winter-like. Mondays highs
only in the 30s are even colder than normal high temperatures in mid
January. The coldest temperatures are likely Monday night when the
surface high is more likely to be overhead leading to calm winds and
potentially a clear sky. Current NBM low temperature forecasts bring
the entire area down into the teens, but if a clear sky and calm
winds develop, sheltered areas could be even colder. Dewpoints in
the single digits suggest an even lower floor if those ideal
conditions develop. A gradual warm up begins Tuesday, so this late
brush with winter only lasts about 36 to 48 hours.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1224 PM CDT Wed Mar 11 2026

Widespread MVFR and occasionally IFR conditions continue behind a
cold front this afternoon. Northwest winds are fairly gusty
especially right behind the front. Some pockets of light rain are
ending quickly and any visibility restrictions will end soon.
Lower clouds dissipate this evening and overnight giving way to
VFR conditions and lighter winds overnight into Thursday morning.


Kimble

&&

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

$$

WFO LSX