985
FXUS63 KLSX 241723
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1123 AM CST Wed Dec 24 2025

.KEY MESSAGES...

- Above normal temperatures are favored through Saturday.
  Confidence is lower than average considering uncertainty in
  exact boundary placement and spread in temperatures from north
  to south.

- A strong cold front will move through the region Saturday night
  into Sunday morning. The Arctic airmass behind the front will
  drop temperatures 40+ degrees by Monday.


&&

.SHORT TERM... (Through Late Thursday Night)
Issued at 331 AM CST Wed Dec 24 2025

Dense fog remains the primary concern across the area this morning.
Recent guidance has struggles with the extend and density of the
fog, particularly in relation to the stalled boundary. This boundary
generally extends west to east across southern Missouri, separating
moisture-rich air with dewpoints well into the 50s to the south,
from drier air with dewpoints in the upper 30s and 40s to the north.
Lingering soil moisture and warm air overrunning cooler surfaces are
fostering fog development along the Missouri River Valley and along
and south of I-70 in Illinois. While dense fog may be less
persistent over the northern tier of the fog advisory, travelers
should remain vigilant as they approach valleys and locations
adjacent to rivers. These areas are more susceptible to rapidly
changing visibility in short distance, while further south dense fog
is more widespread and persistent. Therefore, the fog advisory will
continue through 9AM.

This boundary will continue to be a nuisance through the short term
period. Troughing over the central Plains shift eastward, being
supplemented by strong Gulf ridging to enhance warm air advection.
Warm air advection may result in patchy drizzle or a bring sprinkle,
though measurable precipitation is unlikely with splotchy HREF
probabilities of 10 percent or less supporting measurable
precipitation along the front. Milder temperatures and dewpoints
near 50 degrees will reach as far north as Quincy, IL, with
dewpoints near 60 degrees over southeast Missouri and southwest
Illinois.

The temperature forecast remains challenging, to say the least. The
boundary placement is one things to consider, while another
consideration is the potential for partial clearing to the south. 60-
90% of the HREF ensembles favor highs at or above 60 degrees along
and south of I-70 in Missouri, curving through southwest Illinois.
Confidence in highs at or above 70 are tempered by HREF
probabilities that are all but zero. If 70s do come to fruition,
it`s going to be within the warm sector, where clouds break later
this morning into this afternoon.

The trough over the plains crosses the Upper Midwest late tonight
into Thursday, reinforcing the boundary back to the south. Once
again, fog is looking favorable late tonight into Thursday morning
along and north of the boundary, which roughly parallels I-70. I`m
concerned temperatures might under-perform Thursday with HREF 75th
percentile showing temperatures in the low/mid-50s along the front,
cooling north of the front. No large scale adjustments were made
considering the lower than average confidence in the near term
solutions. I would not be all that surprised to see trends cool
slightly from current forecasts.


Maples

&&

.LONG TERM... (Friday through Tuesday)
Issued at 331 AM CST Wed Dec 24 2025

Temperatures remain quite warm late this week and into the first
half of the weekend. The northward extent of the warmest air, along
with the magnitude of warmth, is somewhat in question. Though the
850MB airmass over the Plains is anomalously warm (2-3 standard
deviations above normal), the orientation and trajectory of the 15-
20C air will be influenced by a trough that traverses the
U.S./Canadian border and into the Great Lakes by Friday, along with
modest flattening of the Gulf ridge.

A weak surface low tracks along the meandering surface boundary
Friday, but has relatively little impact with very weak/no cold air
advection. This leaves some uncertainty with what could end up being
minor temperature adjustments across northern MO and west-central
IL. If there are further temperature adjustments, this would be the
region most likely affected. Much of the remainder of area is south
of the front with less in the way of cloud cover to boot. This leads
to higher confidence in well above normal temperatures (upper
60s/low-70s) south of I-70, supported by 60% of the LREF members at
or above 65 degrees roughly from Jefferson City to Litchfield, IL
and points south. Probabilities drop off significantly to the north.

The Gulf ridge shows modest amplification Saturday, but is expected
to be short-lived. Saturday is nearly a repeat of Friday with
respect to temperatures. Mid-level warmth is ejected more so eastward
than north within what is predominately west-southwest flow. It`ll
be another day well into the 60s across much of the area and low-70s
extending from central MO through far SW IL.

A more pronounced trough and strong surface low gear up to bring a
strong cold front through the central U.S. in the later half of the
weekend. However, there are some timing differences with the front
that suggest that southeast sections of the forecast area may remain
quite warm Sunday morning. What is more certain is that the front
clear the region by Sunday early Sunday afternoon (if not by late
Saturday night). The front doesn`t have a lot of moisture to work
with until it interacts with higher dewpoints (near 60) over
southeast MO and southern IL. Front convergence compresses the
moisture at the back side of the southeastern ridge, leading to a
few showers along the front Sunday morning.

This all brings much colder air back into the region heading into
early next week. NBM IQR are fairly well clustered through Sunday
considering the scenario with spreads increasing next week. At that
time, troughing envelops the northeast CONUS, placing the Midwest at
the western edge of the northwest flow pattern with an amplified
ridge to the west. This will influence temperatures, pending the
amplitude and positioning of both features next week.


Maples

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1122 AM CST Wed Dec 24 2025

Primary aviation impact over the next 24 to 48 hours is the
potential for IFR ceilings and dense fog. A warm front is lifting
north through the region this afternoon, with IFR ceilings along
and north of it. However, clearing has occurred south of it
leading to VFR conditions. Low clouds and fog is expected to
develop again tonight in the vicinity of that front, most likely
affecting areas from Columbia to Quincy. Fog may be dense at
times. A cold front pushing down from the north may bring some
visibility improvement at Quincy by morning, but IFR ceilings are
likely to remain. For St Louis, the lower visibility is more
likely to remain just north of the metro, but could not rule out
the potential for denser fog to develop by morning. Conditions
improve from south to north during the day on Thursday, Christmas
Day, with an eventual switch to southerly winds and potentially a
return to VFR conditions.

Kimble

&&

.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