566
FXUS63 KLSX 061948
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
148 PM CST Sat Dec 6 2025

.KEY MESSAGES...

- Light rain is possible tonight, followed by drizzle for much of
  the day in many areas tomorrow. While we can`t rule out brief
  periods of light frozen precip tomorrow, this appears unlikely
  (20% or less) to cause impacts.

- Temperatures will fluctuate quite a bit this week, from well
  below average Monday, to near or above average Tuesday and
  Wednesday, to much colder Thursday through the weekend.

- Another round of light wintry precipitation is possible (30-60%)
  Thursday, but forecast confidence remains very low.

&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 138 PM CST Sat Dec 6 2025

The primary item of interest in the short term continues to be the
arrival of a modest "clipper" low pressure system from the northwest
this evening and overnight. This system is likely to bring a round
of very light rain tonight, followed by a round of drizzle and
potentially a few snowflakes throughout the day tomorrow, especially
across the higher terrain of the Ozarks

Before we get there, though, quiet conditions are currently in place
this afternoon, with only a steady stream of high clouds hinting at
the approaching clipper. Temperatures have been highly variable
across the area, with temperatures generally remaining in the upper
30 to near 40 north of I-70, with 40s to near 50 across the Ozarks
and southern Illinois. Those latter values are actually near and
perhaps even slightly above average for this time of year, and these
areas likely god a boost from a relative lack of both clouds or
lingering snowpack.

Later this evening, the previously mentioned low pressure system is
expected to quickly scoot along the MO/IA border, bringing with it a
round of very light rain driven largely by isentropic ascent. While
previous forecasts had produced some light accumulating snow with
this initial round, this no longer appears to be likely, as this
system has continued to trend toward a more northerly and slightly
warmer solution in the initial stages. While we can`t rule out some
very light snow along our northern periphery, this appears less and
less likely as now even the 90th percentile of ensemble members
keeps almost all areas snow-free.

Early tomorrow morning, a sharp cold front will usher in a
reinforcing shot of colder air, with steady cold air advection
expected to persist throughout the day Sunday. Because of this,
temperatures are not expected to rise much, if at all, from early
morning lows, and in some areas may even slowly drop during daylight
hours. Meanwhile, a combination of post-frontal lift (assisted by
upslope flow as robust northerlies are forced over the higher
terrain of the Ozarks), substantial low level saturation, and a lack
of cloud ice should produce steadily increasing drizzle in many
areas throughout the day Sunday. Best chances for this will be
across the Ozarks and southwest Illinois, thanks in part to the
upslope flow mentioned previously. While surface temperatures are
likely to be just warm enough for most of this period to keep all of
this liquid, we also can`t rule out a brief period of snow flurries
or even freezing drizzle as temperatures continue to drop,
particularly near and slightly after sunset. While the potential for
impacts remains low, a worst-case scenario featuring stronger cold
air advection could widen the window for frozen precipitation just
enough to produce some local impacts to roads. Still, between the
expected light precipitation amounts and brief window that this
would be possible, this remains unlikely (20% or less).

Temperatures will continue to drop Sunday night thanks to the steady
northerlies, and we can expect morning lows generally in the teens
and low 20s. Most of the drizzle and/or light flurries are expected
to diminish gradually after sunset, but we do note that some CAMS do
maintain some light precipitation through roughly midnight along
our southeastern border, much of which would likely fall as light
snow or flurries if it lingers beyond sunset. Dry conditions are
expected Monday, with temperatures likely only ranging from about
30 to 40 degrees area-wide.

BRC

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 138 PM CST Sat Dec 6 2025

From Tuesday onward, the synoptic pattern will remain remarkably
stable, with a persistent longwave trough positioned across the
eastern CONUS, and northwest flow aloft locally. This will keep out
area within the path of numerous fast-moving clipper systems from
mid to late week, some more substantial than others. This will also
put a ceiling on our temperatures overall, albeit not without
some moderation Tuesday and Wednesday.

On Tuesday, substantial southwesterly flow is expected to develop
throughout the day ahead of our next clipper system, which is
expected to finally bust temperatures back to near and even slightly
above average. In fact, ensemble median temperatures jump almost a
full 20 degrees from Monday to Tuesday, with relatively narrow
ensemble spread as well. While it remains to be seen what, if any,
affect the remaining snowpack will have on temperatures in our
northern areas, high confidence exists that much warmer temperatures
will be felt Tuesday afternoon.

Tuesday night through Wednesday morning, another clipper will move
across the upper Midwest, driving another cold front through our
area and potentially producing some light rain. The northerly track
of this initial wave will likely ensure that both precipitation is
light and that temperatures will be too warm for any of the frozen
stuff, so we don`t expect much in the way of impacts aside from a
modest cooldown Wednesday. However, a deeper, more southerly clipper
is likely to follow shortly thereafter, followed by a much more
expansive cold airmass to close out the work week. While confidence
is low in the timing and track of the wave itself, temperatures
would much more likely to be cold enough to produce wintry
precipitation should that be realized locally. Ensemble
precipitation probabilities remain somewhat low (24 hours PoPs of 20
to 50% chance of .10 inch or more), but this system will need to be
monitored. On the other hand, confidence is increasing that another
multi-day stretch of much colder temperatures will follow to close
out the week, with ensemble mean values falling into the single
digits area-wide by Saturday morning. The specific values are less
certain than the overall trend thanks to the non-trivial ensemble
spread (10-15 degrees), but the trend is quite clear at this
stage.

BRC

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1200 PM CST Sat Dec 6 2025

As of 18Z, LIFR clouds and fog have dissipated at central MO
terminals (COU/JEF), and VFR conditions now exist at all local TAF
sites. This will continue through roughly sunset. This evening and
overnight, a round of light rain is expected to move through UIN
and possibly St. Louis area terminals, followed by periods of
drizzle tomorrow morning through the end of the period. While
there may be some minor visibility reductions with this activity,
the highest-confidence impact at this time appears to be the
development and persistence of MVFR to IFR ceilings, and
potentially even lower at times. The onset time of these low
clouds is not particularly certain, especially at St. Louis area
terminals where low clouds will likely approach from both the
north and the south.

Meanwhile, there is a low-probability (<30%) of some light snow at
UIN this evening and overnight. Drizzle is also most likely (80%)
to remain liquid at local terminals, but we can`t rule out a few
flurries or even very brief freezing drizzle near the end of the
TAF period tomorrow morning and afternoon.

BRC

&&

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

$$

WFO LSX