Area Forecast Discussion
257
FXUS63 KLSX 270402
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1002 PM CST Fri Dec 26 2025
.KEY MESSAGES...
- Warm conditions continue through Sunday before a strong cold
front brings an abrupt return to winter cold.
- Thunderstorms are expected in the vicinity of Sunday`s cold
front, though the threat for severe thunderstorms remains low.
&&
.SHORT TERM... (Through Late Saturday Night)
Issued at 220 PM CST Fri Dec 26 2025
A cold front has moved through the region, and it has been more
noticeable in some areas than in others. Winds have shifted to the
west area wide and dewpoints have begun to fall. Where the sun is
out, it`s warming into the 60s and 70s again, but post-frontal
clouds have prevented deeper mixing across northern MO into central
IL. Places like Quincy actually were within 4 degrees of a record
high as of 7AM, but the temperature has since fallen nearly 10
degrees as low level cold advection is felt more strongly beneath
the blanket of clouds. All areas are seeing the dewpoint fall from
the extreme levels we saw the last few days.
Surface high pressure slides east across Iowa into the Great Lakes
tonight. Although dry advection is at least initially going to be a
negative factor for fog formation tonight, there is some concern
that if the clouds in the north begin to clear this evening then it
won`t take much for us to cool to the dewpoint overnight. As such,
we could see fog development again, this time more of the
radiational cooling variety. High resolution guidance is showing
this fairly aggressively, but confidence remains too low at this
time for the issuance of another Dense Fog Advisory. By Saturday
morning, a southeasterly flow developing around the departing high
begins to bring the moisture back into the region. It will be
seasonably warm once again, though cloud cover development in that
moist advection has the potential to keep things cooler. With that
moist advection continuing overnight we set up one more opportunity
for fog Saturday night, this time of the moist advection variety.
Kimble
&&
.LONG TERM... (Sunday through Next Friday)
Issued at 220 PM CST Fri Dec 26 2025
Big changes come later this weekend. A large trough currently coming
onshore in California joins forces with another trough digging
southeastward out of the Pacific Northwest. They combine to produce
a deeper, stronger trough over the Central US on Sunday. A very warm
and humid air mass is in place ahead of this trough, and the cold
air being dragged in from the northwest is more intense than we`ve
seen in the last two weeks. The result is a very strong cold front
which brings a sharp drop from near-record warmth ahead of it to
subfreezing cold behind it.
With all the moisture in place ahead of the front, and the arrival
of a trough aloft, we also set up the potential for instability to
develop and lead to thunderstorms. With the trough bringing a strong
wind field with it, we`ll have plenty of shear available to produce
more organized and potentially severe thunderstorms. Early day
showers and elevated thunderstorms are most likely along the warm
front which is likely to be just to our north across Iowa into
Illinois. The more uncertain aspect is whether surface based
instability develops ahead of the cold front Sunday afternoon. If
morning clouds from the moist advection hang on, then surface based
instability will be much harder to come by. But if we do get some
clearing and get the temperature to warm to near record highs in the
70s, then surface based instability (CAPE up to about 500) can
develop ahead of the front and lead to a greater severe weather
threat.
One other factor to bring up is that the mid level trough does look
to arrive after the surface cold front. So the arrival of cold air
aloft (to aid in instability) and synoptic scale lift from the
trough may be delayed until after the frontal passage. If storms are
more of the post-frontal variety then they`ll be elevated in nature
and pose a more limited severe weather threat. All of this is to say
that there are a lot of variables that need to line up for a
significant severe weather threat to develop. The latest SPC outlook
maintains a marginal risk (level 1 of 5) across most of our region
which is highlighting this low threat potential Sunday afternoon
into the early evening.
Behind the cold front the temperature takes a big tumble. After
pushing 70 for highs in much of the area, we drop well below
freezing behind the front Sunday night. Precipitation is expected to
shut off as the cold air is arriving, though, which limits the
potential for any change over to wintry precipitation. NBM is
showing a higher likelihood (up to 40 percent) of a change over to
snow before ending, while the low resolution guidance is
considerably more pessimistic about this (only up to 10 percent).
Even if this switch occurs, impacts are not expected as ground
temperatures will remain warm for a time. The incoming air is quite
cold, though, so any moisture left on the ground Sunday night will
have the potential to eventually freeze as the temperature drops.
The cold surface high pushes south into Texas and then nudges east
along the Gulf coast Tuesday into Wednesday. This will keep us
solidly in the cold air through at least Monday, but with some
moderating of the temperature Tuesday into Wednesday. Greater
uncertainty shows up later in the week as another cold front drops
south through the area Wednesday or early Thursday. This front does
latch on to another batch of extremely cold air out of the Yukon,
but the question is whether a significant portion of that is
directed at our region or primarily farther east into New England.
This has led to some rather extreme NBM interquartile ranges for
high temperatures for New Year`s Day, currently at about 20 degrees.
Although still high, this spread has been narrowing (it was 30
degrees just 24 hours ago), indicating some growing confidence. More
of the 12Z ensemble guidance is on the colder side reflecting
greater confidence that this front will in fact arrive in our area
and bring at least some cool down. On the lower end, we`ll be
looking at high temperatures near 20 degrees. On the warmer end,
highs in the upper 30s are still possible, closer to normal for this
time of year.
Kimble
&&
.AVIATION... (For the 06z TAFs through 06z Saturday Night)
Issued at 951 PM CST Fri Dec 26 2025
A Dense Fog Advisory is in effect until 9am for the majority of
the CWA. An expansive IFR stratus deck has continued to hover
over much of the area north of I-70. These clouds were mostly
stationary, but as of 04z have recently begun to expand southward.
Current thinking is that the St. Louis metro and Mid-Missouri
terminals will be impacted by these lower ceilings. Fog has begun
to envelope these terminals as well, with bouncing visibilities
due to overhead high clouds passing. Dense fog is expected to
impact each terminal tonight into tomorrow morning. The only
exception is KSTL, where dense fog is more difficult to achieve
(compared to the river valley sites, at least). Confidence is
lower this site will see dense fog, but it is possible. Fog and
low stratus will dissipate/exit tomorrow with widespread VFR
conditions expected sometime in the afternoon.
Jaja
&&
.CLIMATE...
Issued at 220 PM CST Fri Dec 26 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
12/26 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 Saturday for Audrain MO-Boone
MO-Callaway MO-Cole MO-Franklin MO-Gasconade MO-Jefferson
MO-Knox MO-Lewis MO-Lincoln MO-Marion MO-Moniteau MO-Monroe
MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Saint Charles MO-
Saint Louis City MO-Saint Louis MO-Shelby MO-Warren MO.
IL...Dense Fog Advisory until 9 AM CST Saturday for Calhoun IL-
Clinton IL-Jersey IL-Madison IL-Monroe IL-Randolph IL-Saint
Clair IL-Washington IL.
&&
$$
WFO LSX
NWS LSX Office Area Forecast Discussion
