Area Forecast Discussion

143
FXUS63 KLSX 181117
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
517 AM CST Thu Dec 18 2025

.KEY MESSAGES...

- A cold front brings rain this morning followed by windy and
  colder conditions this evening.

- Mild weather returns this weekend and largely continues through
  Christmas.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 201 AM CST Thu Dec 18 2025

Increased southerly flow this morning in response to a deep trough
in the Northern Plains has brought moisture back into the region.
Dewpoints have risen well into the 40s and low stratus has advected
in with a few showers within the moist southwesterly low level jet
aloft. The surface cold front is only just entering northwest Iowa
at this hour, but will progress quickly southeast reaching the
northern portion of our forecast area around 7AM. A more focused
area of showers along the immediate front itself is expected to
develop as moist low level flow directed into the boundary will be
effective at producing lift. Thus just about everyone will get rain
today as this front moves through, though it may not last long at
any one location. Overall amounts remain light due to this short
duration.

Ahead of the front, mild and humid conditions are expected with
widespread temperatures in the 50s. Behind the front, winds shift to
the west and cold advection begins. This will initiate deeper
mixing, although winds aloft behind the front are not near as strong
as they are in the warm sector ahead of it. So although mixing gets
much more efficient, wind gusts during the morning to early
afternoon are only expected to be around 30 to 35 mph. The
temperature will be falling into the 40s, but deep mixing and a
temporary halt to cold advection limits the temperature fall. A
second cold front pushing north to south reignites cold advection
this evening. It enters our northern area around 6PM pushing quickly
southward. This once again initiates deeper mixing and a round of
gusty northwest winds. This time forecast soundings indicate mixing
to or above 850MB is possible, although winds aloft are only a
modest 35 to 40 KT at that time. Thus even with superb mixing in
cold advection it may be tough to see more than a few brief gusts at
the surface around 45 mph in northeast Missouri into west central
Illinois. In collaboration with neighboring offices we have issued a
Wind Advisory from 3PM to Midnight, although the period of strongest
winds will likely be with the initial frontal passage between about
6PM and 9PM with winds dying down through the night. Temperatures
fall again behind this front, into the 20s or teens by Friday
morning.

Kimble

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 201 AM CST Thu Dec 18 2025

Surface high pressure axis crosses the region early on Friday, so
winds quickly turn westerly and then southerly commencing the warm
up. By Saturday 50s are widespread again. The next cold front moves
in late Saturday, but the core push of cold air behind this one
shoves to the east rather than to the south. So we only get a
glancing blow which knocks temperatures back into the 40s for Sunday
and Monday, near or a bit above normal for this time of year.

Next week guidance is in good agreement on ridging dominating the
central and southern portion of the country leading to a sustained
warm up. This warm up will be warmer than our recent round of mild
weather, with more widespread 60s and even some 70s expected by
Christmas. This is encroaching on record high territory for this
distinctly winter holiday. We have strong confidence that these 70
degree readings will be nearby, though there are some weak frontal
boundaries that dip into the region from the north through the
middle of next week which will limit how far north the really warm
air gets. This is evidenced by the NBM interquartile range for highs
on Christmas Day which is up around 15 degrees at Quincy but only
around 7 degrees at Farmington. This illustrates the greater
uncertainty to the north where frontal position is more likely to
limit warming, while further south there`s greater confidence in
seeing that warm air.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 515 AM CST Thu Dec 18 2025

In the warm sector of the broader storm system this morning exist
widespread MVFR ceilings, although some embedded variation to IFR
or VFR can be expected. A cold front is pushing in rapidly from
the northwest this morning. A line of showers is expected along
the front, but should bring only temporary visibility restrictions
in rain. Winds shift to the WNW behind the front and we should see
ceilings lifting or clearing to VFR. Another cold front pushes
down from the north this evening and will likely bring a brief
ramp up in wind gusts before winds trail off through the night. A
return to MVFR ceilings behind this front is possible, but most
likely in northern areas (like UIN).

Kimble

&&

.CLIMATE...
Issued at 201 AM CST Thu Dec 18 2025

Warm temperatures are expected on Christmas this year. Here are
the record high temperatures for December 25:

LOCATION   REC HIGH    YEAR
St Louis      71       1889
Columbia      74       1889
Quincy        66       2019


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory from 3 PM this afternoon to midnight CST tonight
     for Knox MO-Lewis MO-Marion MO-Monroe MO-Shelby MO.

IL...Wind Advisory from 3 PM this afternoon to midnight CST tonight
     for Adams IL-Brown IL.

&&

$$

WFO LSX

NWS LSX Office Area Forecast Discussion