Area Forecast Discussion

733
FXUS63 KLSX 061429
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
829 AM CST Sat Dec 6 2025

.UPDATE...
Issued at 822 AM CST Sat Dec 6 2025

A blanket of dense (1/4 mile or less) fog has expanded into parts
of Central Missouri early this morning, and based on satellite and
surface observation trends, we have added a few local counties to
an ongoing Dense Fog Advisory in central Missouri until 10 am.
While we do not expect fog to last much beyond this time, the fact
that coverage continues to expand and visibilities have not yet
shown signs of improving as of 8 AM, we opted to hoist a short
Advisory. In addition, while we don`t expect freezing fog to
become a widespread concern, there is some limited potential for
very light freezing fog/frost accumulations on elevated surfaces,
as temperatures in this area are roughly 4-6 degree2 below
freezing as of 8 am.

BRC

&&

.KEY MESSAGES...

- The temperature this weekend and into next week bounces between
  seasonably mild and bitter cold and back again.

- Precipitation chances this weekend have decreased compared to
  earlier forecasts. Significant precipitation is not expected
  through the middle of next week.


&&

.SHORT TERM...  (Through Saturday Night)
Issued at 136 AM CST Sat Dec 6 2025

A cold front has begun to slip into our region from the north early
this morning. It won`t make it very far south before stalling around
midday. It will, however, serve to stunt the recent milding
temperatures in the north, with highs only making it into the 30s
generally across the still snow covered half of the forecast area.
Further south it will be another somewhat mild day by recent
standards, though still a few degrees below normal.

A quick moving trough exits the Northern Rockies and moves southeast
into the Plains today, then crosses the Mississippi River tonight.
The southerly flow ahead of this trough pushes the remnant front
back to the north as a warm front overnight, with the surface low
tracking near the Iowa/Missouri border. This further north track
compared to prior forecasts limits our precipitation potential with
this wave, as the bulk of the precipitation falls in bands north of
the warm front roughly from Des Moines to Chicago. Any precipitation
we get out of it will be from warm advection in the warm sector
south of the front. This will be less organized and warmer. So
expect a few sprinkles or rain showers overnight, but not much more
than that. The best potential for snow remains across the far
northern fringes of the forecast area, but even here chances have
decreased significantly due to the shift in track further north.
Among the 12Z low resolution ensemble guidance, less than 50 percent
of members now produce measurable snowfall at Quincy. None of the
high resolution guidance does so.

Kimble

&&

.LONG TERM...  (Sunday through Thursday)
Issued at 136 AM CST Sat Dec 6 2025

A much colder air mass will be pulled southward behind Sunday`s
wave. In fact, some areas may see falling temperatures Sunday
afternoon with temperatures bottoming out in the teens and single
digits by Monday morning. The surface high associated with this air
mass crosses through our area on Monday, so after one more cold day,
we see a dramatic warm up in southwesterly flow behind the high for
Tuesday. NBM probability of 50 degrees has increased compared to
yesterday`s forecast, with most areas south of I-70 in Missouri at
50 percent or better chance of reaching that threshold. That`s a
good 15 to 20 degrees warmer than Monday.

The next significant trough moves through the Upper Midwest into the
Great Lakes Tuesday into Wednesday. Once again this wave tracks to
our north, limiting our precipitation chances with it. If we do get
anything it will be rain as we will be solidly in the warmer air by
that point. However, this trough does once again send a cold front
southward behind it with a sharp cool down expected for the end of
the week. There continues to be rather large spread in guidance on
just how cold we get, but there`s strong agreement that we do get
cold. The NBM interquartile range for high temperatures rises to
about 15 degrees Thursday and Friday indicating that much higher
uncertainty. However, it`s worth noting that while that spread
ranges from the upper 20s to mid 40s for highs on Thursday, it drops
10 degrees for Friday, ranging from the upper teens to the mid 30s
for highs. Lows have similar levels of uncertainty on them, with NBM
probability of subzero lows rising to as high as 30 percent in our
northern forecast area.

While Wednesday`s wave passes by to our north while we`re still in
the warmer air, guidance is starting to come into some alignment on
the idea of a secondary wave coming down in the northwest flow
behind it on Thursday while we`re in the freshly colder air. There`s
a lot of timing and track variance still, but most guidance does now
show this wave in some form. This will serve as our better chance of
wintry precipitation, most likely in the form of light snow,
provided this wave tracks through our area. Among the 12Z low
resolution ensemble guidance, 50 percent or more of members produce
measurable snowfall in the 24 hours ending Thursday evening, and
even the deterministic NBM forecast is beginning to reflect this
with 20 to 30 PoPs.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 519 AM CST Sat Dec 6 2025

The MVFR cloud deck out of Iowa has sunk into much of the forecast
area north of I-70. Erosion and regrowth this morning has been
making forecasting the deck`s exact behavior and timing difficult.
For instance, a cloud deck has rapidly developed in northeast
MO/west-central IL north of KSTL and is pushing east- southeast.
Current satellite shows erosion on the deck`s backside and
expansion along its front, increasing confidence in brief MVFR
conditions at KSTL this morning. Confidence wanes concerning KSUS
and KCPS, given that the eroding back-end of the deck would be
what passes over these terminals.

Otherwise, expect a wind-shift from westerly to southeasterly
today and an increasing potential for light rain with lowering
ceilings tonight. KUIN has the highest potential at seeing light
rain. There is a very low potential that this site sees a very
brief rain/snow mix as well, but models are trending away from
this. Further south and west the potential for light rain
decreases significantly, so decided against mentioning it anywhere
else.

Jaja

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 10 AM CST this morning for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Moniteau MO.

IL...None.
&&

$$

WFO LSX

NWS LSX Office Area Forecast Discussion