Area Forecast Discussion
323
FXUS63 KLSX 231143
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
543 AM CST Tue Dec 23 2025
.KEY MESSAGES...
- Unseasonably warm temperatures are forecast today through Saturday.
There is however uncertainty each day with exactly HOW warm
each day will be and if any record highs will be set.
- A strong cold front moves through late Saturday, with temperatures
35-40+ degrees colder Sunday into Monday.
&&
.SHORT TERM... (Through Late Tonight)
Issued at 302 AM CST Tue Dec 23 2025
A weak cold front is currently draped across the mid-Missouri
Valley into the Upper Midwest very early this morning. This
boundary is expected to sag southward through the day today before
stalling out across far southern Missouri into the lower Ohio
Valley. This is a Pacific "cold" front, with very weak low-level
cold air advection and no significant air mass change behind the
boundary. Therefore, warmer temperatures are forecast today
compared to yesterday, with highs ranging from the upper 50s to
mid 60s from north to south. Low stratus may linger across
portions of southeast Missouri and southwest Illinois into the
afternoon, which could hamper the warmup. This is where there is a
bit more uncertainty within the CWA. More sunshine than expected
could yield highs closer to 70 degrees while thicker stratus
staying well into the afternoon could keep highs closer to 60
degrees.
The quasi-stationary surface boundary looks to remain across far
southern Missouri/Illinois overnight tonight, though may begin to
push northward late. Increasing low-level moisture and persistent
convergence along this boundary may be enough to produce some
drizzle beneath the low stratus. Added drizzle wording for overnight
tonight due to this signal. Lows tonight are expected to vary quite
significantly across the boundary (and this will be a running theme
in the days/nights ahead). Parts of northeast Missouri/west central
Illinois are expected to drop back into the mid 30s well north of
the front and where the night is expected to be clear until roughly
midnight. Lows warm with southern extent, with temperatures only
bottoming out in the low to mid 50s across parts of
central/southeast Missouri. This is where the front may move through
overnight and where low stratus should advect into the area first.
Gosselin
&&
.LONG TERM... (Wednesday through Monday)
Issued at 302 AM CST Tue Dec 23 2025
(Wednesday - Saturday)
While unseasonably warm temperatures will continue through Saturday,
there is quite a bit of uncertainty each day on exactly HOW warm it
will be. Uncertainty resides due to two primary reasons: 1) the
position of the quasi-stationary front and 2) clouds. The air mass
in place is about as impressive for late December as it gets,
characterized by record high 500-hPa heights and 850-hPa
temperatures above the 99th percentile of climatology. In other
words, the air mass is favorable for record-breaking warmth, but
surface or near-surface subtleties such as the exact frontal position
each afternoon and the prevalence of stratus (as well as higher
level clouds) will ultimately determine how warm it gets each day.
The problem is, the further out in time you go the uncertainty gets
larger with each of these variables. Just look at how Christmas Day
looked literally 48 hours ago. The frontal position looked to be
along I-80 Christmas afternoon. Now, it appears likely to be
slightly SOUTH of I-70. In other words, the expected position of the
quasi-stationary front has shifted in model guidance about ~200
miles! This shift south is mainly due to a stronger midlevel
shortwave trough moving across southeast Canada late tonight/early
Wednesday morning. The associated surface low downstream of this
feature is in turn stronger, and more able to push the boundary
further to the south.
It still remains likely that the frontal boundary will shift at
least slightly northward during the day on Wednesday, aided by weak
leeside cyclogenesis across the western Plains. How far north (and
how fast) are open question marks. At this point in time, the
boundary should move north into northeast Missouri/west central
Illinois by late afternoon. Thick low-level stratus along the
boundary will hamper the warmup however across much of the northern
1/2 to 2/3 of the bi-state area. Stratus is not expected to advect
out of these areas until late afternoon, if not later. So, what does
this mean for highs Wednesday? Highs in the mid 50s to low 70s are
forecast from northeast to southwest, though the confidence is lower
than normal for a forecast only 36 hours away. The spread on the
inter-quartile range of the NBM is in the 5-8 degree range, and
closer to 7-10 degrees between the 10th/90th percentiles.
Most deterministic guidance shows some type of weak surface wave
moving across the frontal boundary Wednesday night. Behind this
wave, the front sinks back south, most likely across southeast
Missouri and southwest Illinois by Christmas morning. Unlike during
the day on Wednesday, there does not appear to be any real coherent
signal for the boundary to lift back north Christmas Day. This isn`t
expected to happen until later on that night as a weak midlevel
shortwave ejects out of the central Plains and induces another weak
surface low to lift the front back northward. With the front likely
south of I-70 AND a strong signal for thick low-level stratus along
the boundary, high temperatures for Christmas Day itself are 5-10
degrees cooler than 24-48 hours ago. Highs are expected to range
from the mid 50s to low 70s from north to south, though many areas
still are probably too warm if the frontal position is indeed south
of I-70 AND the stratus is in place during the day. It usually is
very difficult to accurately depict the temperature gradient from
north to south in these scenarios, and reality is typically much
tighter/stronger than what is forecast when using blended guidance.
Chances of record highs, which seemed quite likely a day or two ago,
have dropped significantly at all 3 climate sites, but especially
KUIN where chances now are close to zero.
The running theme of where is the quasi-stationary front and how
does it evolve lasts into early this weekend. The weak surface wave
moving along the front late Christmas night is expected to help push
the front at least into northern sections of the area. This suggests
a very mild night heading into Friday morning, with lows only
dropping back into the 50s areawide (~30 degrees above normal).
Friday afternoon`s highs are very likely to be warmer everywhere,
but again, how warm. This will depend on how fast the boundary moves
back south behind the departing surface wave. Currently, southern
sections of the area should reside south of the boundary during peak
heating and therefore should be warmest (>70 degrees). Given the
warmer highs expected compared to Christmas Day and lower records
for 12/26, all 3 stations may flirt with or break daily records. I
will caution however that the exact timing of this surface wave and
subsequent push back southward of the frontal boundary is not a
certainty. A slightly faster wave would likely yield high
temperatures at least several degrees cooler than forecast. The
spread on the IQR from the NBM is larger than the next few days, on
the order of 7-10 degrees. The current forecast resides near the
75th percentile of the NBM. If there is any quicker shift southward
with the boundary, Friday`s highs may be some 3-5 degrees too warm
in many areas.
Friday night`s lows should be at least 5+ degrees cooler than
Thursday night as the front shifts back closer to southeast
Missouri/southwest Illinois once again. Another push north is
forecast on Saturday, but like Wednesday, how far north and how
quickly? Saturday may actually have the most potential to be the
warmest day of this 5-day stretch IF the boundary can move north
quick enough. A stronger surface wave is expected to move along the
boundary Saturday afternoon. This helps veer the winds more to the
southwest, which downslope off of the Ozark Plateau. The
deterministic GFS shows this scenario well, with widespread low to
mid 70s for forecast highs. Meanwhile, the ECMWF is slower with the
retreat of the boundary and keeps highs more in the upper 50s to mid
60s.
(Saturday Night - Monday)
What is more of a certainty is that this 5-day stretch of
unseasonable warmth will come to an abrupt end behind Saturday
night`s cold frontal passage. Ensemble guidance has trended stronger
with the mid/upper level wave coming across the US-Canadian border.
Mean 850-hPa temperatures of -5 to -9C are forecast on the LREF,
with the GEFS slightly colder than the EPS. The incoming surface
anticyclone is also seasonably strong (1032+ hPa; >90th percentile
of climatology). While this incoming air mass does not look too
terribly impressive for late December, it certainly does in
comparison to the next 5 days. Both low and high temperatures Sunday
night into Monday are likely to be about 35-40+ degrees colder. Add
in strong northwest winds and it will feel more like 45-60+ degrees
colder! Probabilities for subzero wind chill values late Sunday
night/early Monday morning on the LREF are in the 10-30% range
along/north of I-70 and have consistently been trending up over the
past 48 hours.
Gosselin
&&
.AVIATION... (For the 12z TAFs through 12z Wednesday Morning)
Issued at 533 AM CST Tue Dec 23 2025
Fog and low stratus are the primary concerns through the morning
hours. Central Missouri sites should see impacts within the next
couple of hours. Ceilings below 1 kft AGL with visibilities at
times below 1SM are forecast. Advection into the metro St. Louis
terminals looks likely by later this morning, but should be more
stratus vs. fog by that time. Ceilings around 1000 feet may occur
from mid to late morning. VFR conditions are expected this
afternoon as conditions gradually improve. A weak front will stall
out across the area tonight, with winds mostly light/variable.
Another round of low stratus, and possibly fog, looks to expand
north after midnight toward central Missouri and metro St. Louis.
Gosselin
&&
.CLIMATE...
Issued at 220 PM CST Mon Dec 22 2025
Well above normal temperatures are expected for much of Christmas
week. Record high temperatures are within reach on several days.
Daily record highs for each site are listed below.
St Louis Columbia Quincy
12/2473(2021)74(2021)69(2021)
12/2571(1889)74(1889)66(2019)
12/26 70(1942) 69(1942) 63(1942)
12/27 72(1971) 71(1946) 70(1946)
The all time December record highs are listed below.
St Louis - 76 most recently on Dec 3, 2021
Columbia - 76 most recently on Dec 15, 2021
Quincy - 75 on Dec 15, 2021
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX
NWS LSX Office Area Forecast Discussion
