248
FXUS63 KLSX 070804
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
204 AM CST Sun Dec 7 2025

.KEY MESSAGES...

- The temperature falls behind a cold front this morning bringing
  winter-like temperatures through Monday. A brief warm up comes
  Tuesday and Wednesday before the cold returns again.

- A weak wave on Thursday will bring light snow to parts of the
  region. MUCH colder air moves in for the weekend.

&&

.SHORT TERM... (Through Tuesday)
Issued at 200 AM CST Sun Dec 7 2025

Surface low pressure is tracking east across northern Missouri this
morning. To the north of the low track, widespread snow is falling
across Iowa into northern Illinois, but this has largely missed our
area to the north. Behind the low, a cold front is pushing southward
through the Plains, and as the low exits east this morning we`ll see
that front drop through our area from north to south. North of I-70
this front moves through near or before daybreak, with the
temperature holding steady or falling through the day. South of I-70
it`ll be more mild with a few hours to warm up a touch more before
the cold front comes in. The result is a strong gradient in high
temperatures today. Some low level moisture does wrap around the
departing low and we`ll see that primarily in the form of clouds, or
perhaps a sprinkle or flurry. But this is not expected to be
impactful if it occurs.

Surface high pressure builds into the Great Lakes tonight and then
pushes into the Northeast on Monday. This will set up our coldest
night tonight, when temperatures will be in the teens and single
digits area wide with a persistent northerly wind. Southerly return
flow begins on Monday as the surface high moves east, but the warm
up won`t really be noticeable until Tuesday when we warm some 20
degrees or more, into the 40s and 50s area wide. That`s the warmest
weather we`ve seen since before Thanksgiving.

Kimble

&&

.LONG TERM... (Tuesday Night through Saturday)
Issued at 200 AM CST Sun Dec 7 2025

After a warm up Tuesday into Wednesday in briefly zonal flow,
troughing becomes reestablished later this week with a return of the
winter cold. A robust trough moving through the Great Lakes on
Wednesday will drag a cold front southeast behind it. Guidance
continues to pull back on our rain chances with this as the better
forcing remains well to our north over the Great Lakes. However, it
will put an end to our brief warm up and send the temperature
falling again.

The initial front on Wednesday gives us more of a glancing blow from
the cold air, with the core of this cold pushing more to the east
into New England. In fact, the front may not even make it all the
way through our area as it stalls and briefly lifts back north as a
warm front on Thursday as the next shortwave trough moves through
the northwest flow aloft. This wave is similar to the last few that
affected our area, of the "Clipper" style with the bulk of the
precipitation falling along and north of the surface warm front.
That of course will also be where the cold air will be, with the
bulk of the precipitation falling as snow, potentially changing to
rain as the temperature briefly warms. The primary uncertainty with
this wave is where it will track as well as some timing uncertainty.
Most guidance does suggest this wave will take a more southerly
track than this morning`s wave did, but with 5 more days of
variables to resolve we don`t have strong confidence on impacts
locally yet. Among the 12Z ensemble guidance, up to 70 percent of
members produce measurable precipitation across the bulk of our
forecast area on Thursday, but amounts remain light. Less than 30
percent of members produce more than 0.1 inch of precipitation,
roughly corresponding to 1 inch or more of snowfall.

After Thursday`s wave, another cold front gets shoved southward with
even colder air behind this one. This time the cold air takes better
aim at our area with much colder air lasting through the weekend. At
this point it`s looking like we`ll see another 3 days or so with the
temperature not warming above freezing during the day, and
potentially falling to near zero degrees at night. There`s still
uncertainty on just how cold it gets, with NBM interquartile range
for both highs and lows remaining high (more than 10 degrees)
through this period. But guidance has been trending colder over the
last several forecast cycles with more members getting on board with
the colder scenarios. Looking at the probabilistic NBM, on the
warmer end of things (90th percentile) we`re still looking at at
least 2 days with high temperatures near freezing. On the colder end
(10th percentile) we`ll see at least 3 days below freezing, with
highs closer to 10 degrees. The probability of subzero low
temperatures has risen to 40 percent or higher from I-70 northward
this weekend. Those colder scenarios will be further enabled if we
get a fresh snow cover laid down on Thursday.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 937 PM CST Sat Dec 6 2025

Little change in thinking from last update. MVFR ceilings are
moving northward ahead of a low pressure system which will move
across Missouri into Illinois tonight and Sunday morning. Another
area of low MVFR/IFR ceilings will move south out of Iowa behind
the low and its trailing cold front. These two areas of low clouds
will eventually meet in east central Missouri/southwest Illinois
Sunday morning. Low MVFR/IFR ceilings will then prevail through
00Z. Patchy drizzle is also possible for much of the day Sunday.
Drizzle is expected to mix with and possibly change over to snow
flurries before ending. Precipitation is expected to be light
enough to have little to no impact on airport operations. Guidance
suggests that the low ceilings will begin clearing from north to
south after 00Z Sunday...although the improvement will be slow
and may not reach the I-70 corridor before the end of the period.

Carney

&&

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

$$

WFO LSX