Area Forecast Discussion
784
FXUS63 KLSX 252323
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
523 PM CST Thu Dec 25 2025
.KEY MESSAGES...
- Another night of fog and clouds is expected tonight, but more
clearing is expected area wide tomorrow with warm temperatures
continuing into the weekend.
- A very strong cold front on Sunday brings a round of
thunderstorms followed by Arctic cold. The temperature will
drop some 50 degrees bringing an abrupt return to winter cold.
&&
.SHORT TERM... (Through Late Friday Night)
Issued at 208 PM CST Thu Dec 25 2025
Highly anomalous ridging continues across the central US today with
extremely warm temperatures aloft near the climatological maximum
for this time of year. The air mass at the surface, though, is also
extremely moist. 60s dewpoints have been trying to invade our area
for a few days now, also near the climatological maximum for this
time of year. That kind of moisture is hard to sustain through our
long nights, especially with a shallow, cool surface layer
entrenched. The result has been fog and clouds developing in the
evenings and lasting through the mornings, with some breaks in the
clouds in the afternoons. This trend continues for one more night
tonight, as our slow moving surface boundary tries once again to
lift northward overnight. This reinforces the inverted moisture
profile as warm, moist air slides up and over the cool surface air,
generating widespread clouds and fog. Latest NBM forecast shows
temperature and dewpoint rising overnight in our northern forecast
area which is another red flag for fog potential. Latest high
resolution ensemble data shows the potential for dense fog across
the northern half of the forecast area, with 50 percent or more of
members producing 0.5 mile or less visibility at times tonight.
Considering our confidence in the set up, and the history of the
last several nights, we have extended the Dense Fog Advisory for
parts of northeast MO into west central IL through Friday morning.
Fog may develop further southward as well, but confidence is lower
at this time.
The moisture is pushing northward overnight in response to an
increased southerly flow ahead of a weak surface low emerging out of
the lee of the Rockies today and tracking east toward the Great
Lakes tonight. With ridging aloft holding strong over our area,
we`re not expecting any significant rainfall out of this wave in our
area, but the passage of the surface trough will cause a shift to
westerly winds which will finally push away the extreme moisture
Friday morning. Dewpoints drop some 10 to 15 degrees. With more sun
expected area wide and thus deeper mixing, most areas will warm into
the 60s and 70s as the warmth from the ridge is more accessible
overhead.
Kimble
&&
.LONG TERM... (Saturday through Next Thursday)
Issued at 208 PM CST Thu Dec 25 2025
Big changes are coming this weekend. A trough currently bringing
heavy precipitation to the West Coast will move through the
Intermountain West on Saturday. Another trough dropping south out of
western Canada joins forces with this trough as it moves into the
central US on Sunday, generating a much deeper trough that moves
through the Great Lakes early next week. The mass response to the
incoming trough begins across the Plains on Saturday as a surface
lee trough drives renewed southerly flow to its easy. This pushes
the extreme moisture back north through our region with continued
warmth near seasonal record levels. Low level moist advection again
spells the potential for low clouds and fog, especially Saturday
night.
This time of year, often if we get extremely warm and humid
conditions it ends in thunderstorms which can be strong to severe.
Up until a few days ago, it actually looked like we might sneak out
of this round of moisture without that result. But over the past 2
days or so, guidance has converged around the idea of a much deeper
(and slower) mid level trough which brings greater forcing for
precipitation. With low level moisture maximizing ahead of the
incoming surface front and cold air aloft arriving with the trough,
we also start to generate instability along the frontal zone for the
potential for thunderstorms. With these new developments, our
forecast for Sunday has continued to trend warmer while rain chances
have really ramped upward. Nearly 100 percent of the low resolution
ensemble guidance produces rain across our region by Sunday evening,
and up to 50 percent produce 0.5 inches or more.
The rain may be somewhat welcome considering the recent trend of
only getting meaningful rain once every couple of weeks since the
start of fall, but the more concerning aspect is the potential for
severe thunderstorms. While low resolution guidance still maintains
limited instability, it does not take much instability in the
presence of strong wind shear to produce organized severe
thunderstorms. Latest SPC outlook does not highlight this period yet
as there is uncertainty as to whether any storms that form will
occur ahead of or just behind the front. However, it`s worth noting
that the strong, dynamic system will bring with it plenty of wind
shear, and if surface based instability becomes accessible then a
greater severe weather threat can materialize quickly. Among the
GEFS and EPS members, up to 10 percent produce at least 500 CAPE
Sunday afternoon along the cold front, sufficient for a notable
severe weather threat.
This cold front is quite a doozy. The air mass that has been
building across northwest Canada and eastern Alaska has been extreme
even by their standards, with readings of 50 below or colder
observed yet again this morning. A piece of this air mass is getting
caught up in the evolving trough this weekend, with the cold air
arriving quickly behind Sunday`s cold front. So while some areas
make another run at 70 degrees ahead of the front on Sunday, all
areas fall back into the 20s Sunday night into Monday morning, and
don`t warm above freezing at all on Monday. That`s a sharp 50 degree
drop to remind us that it is in fact winter. Most guidance has the
precipitation ending before the cold air arrives, but up to 20
percent of low resolution ensemble members do show a brief switch to
snow before precipitation ends. With strong winds accompanying the
cold front, wind chill values may fall below zero especially in
northern areas by Monday morning.
The surface high associated with this air mass is rather quick to
push through the region Monday night, so this initial blast of
Arctic cold will be somewhat brief. A bounce back to near or even
above normal temperatures is expected by midweek. Ridging takes hold
over the western US while troughing dominates the eastern US. Our
area is caught in the middle in a dry northwest flow. Additional
pieces of cold air get pulled into the eastern trough over the
coming week, but how much our area is affected by them remains more
uncertain. Latest ensemble guidance is trending toward the more mild
scenarios for our area, with the cold air masses being directed more
toward New England than the Mississippi Valley. Of the 00Z ensemble
clusters, only about 20 percent of members are grouped with the cold
solution for our area, while the remainder keep temperatures
seasonably mild through the New Year. NBM interquartile range for
temperatures remains quite extreme, nearly 30 degrees on New Years
Day, with the difference being highs in the 50s or below freezing.
Kimble
&&
.AVIATION... (For the 00z TAFs through 00z Friday Evening)
Issued at 516 PM CST Thu Dec 25 2025
A warm front is slowly lifting northward across the region, and is
the current driver of stratus and fog for portions of the area.
The last local terminal north of the front is KUIN, where fog is
favored through much of the overnight period. Though, this fog is
expected to thin slightly as the warm front drifts northward.
Intermittent low stratus will also skim the metro St. Louis area
to the east, mainly impacting KCPS through this evening, though
brief impacts also can`t be ruled out at KSTL and KSUS. A dry cold
front sweeps over the local terminals during the day tomorrow,
with moisture pooling along it bringing a brief bout of MVFR
stratus to the local terminals. In the wake of the front, deep
mixing will improve flight conditions to VFR for the remainder of
the period.
Elmore
&&
.CLIMATE...
Issued at 208 PM CST Thu Dec 25 2025
Well above normal temperatures continue. Record high temperatures
are within reach through Sunday. Daily record highs for each site
are listed below.
St Louis Columbia Quincy
12/2571(1889)74(1889)66(2019)
12/26 70(1942) 69(1942) 63(1942)
12/27 72(1971) 71(1946) 70(1946)
12/28 75(1928) 71(1984) 70(1984)
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...Dense Fog Advisory until 9 AM CST Friday for Knox MO-Lewis MO-
Marion MO-Monroe MO-Pike MO-Ralls MO-Shelby MO.
IL...Dense Fog Advisory until 9 AM CST Friday for Adams IL-Brown IL-
Pike IL.
&&
$$
WFO LSX
NWS LSX Office Area Forecast Discussion
