953
FXUS63 KLSX 050815
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
215 AM CST Fri Dec 5 2025

.KEY MESSAGES...

- We warm up back above freezing today, but still below normal for
  early December. Cool to cold temperatures continue into next
  week.

- A quick system brings light snow to parts of the region Sunday
  morning.

&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 213 AM CST Fri Dec 5 2025

After an epic start to Winter with 4 of the last 5 days staying
below freezing, we`ll see a warm up today. Surface high pressure
moving to the East Coast opens up a southwesterly low level flow
across our region with a westerly flow aloft pushing aside our
recent cold air. While we`ll be 15 to 20 degrees warmer this
afternoon compared to yesterday afternoon, it`s still several
degrees below normal for early December. Daytime highs in the mid
30s to mid 40s and a good deal of sunshine will allow for some
melting of the remaining snow cover.

A trough moving through Canada and the Great Lakes will send a cold
front southeast through the Plains and arrive in our area on
Saturday. So for tonight we`ll remain in the southwesterly flow with
much milder temperatures, though still likely dipping just below
freezing. Once the front moves in early Saturday it will hold
temperatures much colder in the northern part of our forecast area,
near freezing for highs with plenty of clouds. The front stalls
somewhere across the middle of our forecast area, and areas south of
the front will see temperatures similar to today, in the 40s, never
really getting in on this latest cold air mass.

Kimble

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 213 AM CST Fri Dec 5 2025

While the next few days will be warmer than we have been, the long
term forecast continues to look cool or even downright cold at
times. Although daily temperatures vary, long wave troughing remains
across the central to eastern part of the US keeping cold air either
in place or not far away right through the end of next week. Even on
our warmest days we`ll be topping off near average for this time of
year, but on the colder ones we may not get above freezing.

Saturday`s front stalls somewhere across the center of our forecast
area as a shortwave trough moves southeast out of the Northern
Rockies and into the Plains. This sets up a southerly low level flow
to push the remnant front briefly northward as a warm front before
surging back south again after the wave passes by. Guidance is in
good agreement that this wave will bring a short (less than 12 hour)
period of precipitation with it Sunday morning, generally along and
north of the surface frontal boundary as the advancing wave links up
with moisture return from the Gulf. Guidance is in generally good
agreement on the track of this wave and the general position of the
front, focusing the core of the precipitation across Iowa and into
central Illinois. Our forecast area is on the southern fringe of
this one, though areas from Quincy to Litchfield have a strong
chance of seeing meaningful precipitation. Among the long range
ensemble guidance, 70 percent or more of members produce at least
0.05 of liquid equivalent precipitation along and north of a line
between those two cities. Further south, the chances decrease
considerably.

Precipitation will be predominantly snow, though the warm advection
will lead to warming temperatures which will tend to change things
to rain during the morning hours before the cold air surges back in
behind the cold front in the afternoon. This set up is actually
quite similar to what we saw last Saturday with snow changing to
rain in the morning hours as the temperature briefly warms, though
it`s notable that we are not expecting nearly as much total
precipitation with this one as the moisture available is more
limited. Some guidance does indicate the potential for a brief
period of freezing rain along the southern fringe of the
precipitation, though I believe this to be a bit overstated. Like
last Saturday, wind flow ahead of this system will be out of the
east or southeast, unable to lock in the cold air in the low levels
and set up the necessary inversion to produce significant freezing
rain. It`s more likely that as the temperature aloft warms above
freezing, the temperature at the surface will as well, leading to a
smoother transition from snow to rain. Any potential areas of
freezing rain are likely to be brief and fleeting as the temperature
warms Sunday morning.

As far as amounts go, we`ll be limited by the available moisture and
the relatively quick nature of this system. Long range low
resolution guidance is narrowing in on a swath of 0.2 to 0.4 inches
of liquid equivalent in the core of the precipitation, which again
is currently forecast just to our north across Iowa into central
Illinois. While forecast amounts in our area are currently less,
this is primarily due to the current tracks favoring areas just to
our north with the heavier precipitation. If this band shifts a bit
south, then the Quincy area would get in on some of the more
significant snowfall. At this point we have fairly high confidence
in at least some minor snowfall in our northern CWA (up to 1 inch),
though there remains a lower potential (15 percent or less) for more
significant amounts of 3 inches or more.

As the wave pushes east on Sunday, cold air will rush back in behind
it. We may see temperatures fall from their morning values back
below freezing in the afternoon, and well below freezing Sunday
night. In fact, the probabilistic NBM is advertising 20 to 40
percent chances of the low temperature falling below zero in the
north. Those chances are enabled by high pressure settling in
quickly overnight and would be further enhanced by a fresh snow
cover. However, lingering cloud cover could prevent stronger cooling
and keep temperatures from dropping as cold. Although it`s quite
cold behind Sunday`s front, it doesn`t last long. High pressure
exits to the east late Monday and a warm up begins again. By Tuesday
a stout southwest flow will advect much warmer air into the region.
The probabilistic NBM is showing 30 to 60 percent probability of the
temperature reaching 50 degrees generally south of I-70 in Missouri.

The next big weather maker is a potent trough moving into the Great
Lakes Tuesday night into Wednesday. The core of this trough passes
well to our north, so our precipitation chances are low at this
point. With our area solidly in the warm air it would be primarily
rain if it occurred. However, the cold air isn`t far away and
Wednesday`s system will begin to pull that cold air back down again.
There is some variance in the guidance on how quickly the cold air
pours in and just how intense the cold air will be. The 00Z
operational GFS is notably colder than the operational ECMWF
Thursday into Friday. The NBM interquartile range for high
temperatures surges from 4 to 6 degrees most of the week to 15
degrees or more by Thursday indicating much greater uncertainty. So
while we know it will get cold again, we`re less sure just how
cold.

Kimble

&&

.AVIATION...  (For the 00z TAFs through 06z Friday Evening)
Issued at 900 PM CST Thu Dec 4 2025

VFR flight conditions are expected to prevail through the period.
There is a small area of MVFR ceilings with bases around 2000ft
AGL over south central Illinois. Guidance suggests that it may
spread a little farther to the west-northwest this evening before
being pushed to the east as low level flow turns to the west-
southwest after 06Z. One member of the hi-res model suite
continues to show spotty IFR visibilities in northeast
Missouri/west central-south central Illinois tonight. However it`s
the only one, so confidence in any fog remains low (<20%). Again,
if fog does form, temperatures will be below freezing which will
promote icing on wing surfaces. Light and variable flow at the
surface will become southerly, on Friday and continue to veer to
the southwest on Friday evening.

Carney

&&

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

$$

WFO LSX