643
FXUS63 KLSX 121725
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1125 AM CST Wed Nov 12 2025

.KEY MESSAGES...

- A combination of dry and gusty conditions will likely (80%
  chance) overlap from northeast Missouri through south-central
  Illinois this afternoon, promoting an elevated fire danger.

- Unseasonable warmth builds this week, with near-record
  temperatures arriving Saturday.

- After what now looks to be a dry weekend, the best rain chances
  (40-60%) center on Monday-Tuesday.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 217 AM CST Wed Nov 12 2025

A weak surface ridge is gradually building from the west over the
Mid-Mississippi Valley behind an equeally-weak cold front that
passed through overnight. Dry northwesterly flow aloft is promoting
clear skies (and unobstructed aurora-viewing) areawide. A weak
but persistent westerly wind is keeping temperatures several
degrees warmer than this time yesterday. The limited cloud cover
will continue today, allowing for insolation to overcome weak
cold air advection depicted in most guidance to warm temperatures
into the 60s areawide (5-10 degrees above yesterday`s highs).

The stronger insolation and warmer surface temperatures will allow
for some deeper boundary layer mixing, particularly north of I-70
where 0-2km lapse rates are uniformly modeled a tad stronger.
This will promote gusty winds, particularly across northeast
Missouri west-central/south-central Illinois. Deterministic NBM
winds fall fairly low on the broader distribution of guidance,
around the 25th percentile, including even the more conservative
CAMs. As a result, values were raised a bit to capture the
increased threat for 15mph sustained winds with gusts to 25mph.
The deeper mixing will also promote lower humidity than previously
forecast, and the dry/windy combination in the aforementioned
areas will promote an elevated fire danger late this morning
through the afternoon. High-resolution ensemble guidance, which
does fairly well in these situations usually, points to high (80%)
probabilities of the sufficient RH/wind speed combination to
support this impact. Please refer to the Fire Weather Forecast
(FWFLSX) for a more technical discussion.

Winds slacken overnight as diurnal mixing ends and surface high
pressure becomes more established. This feature quickly scoots east
by Thursday morning, with southerly boundary layer winds becoming
established. The resultant warm air advection will further support
abnormal warmth through the day. While increasing cloud cover will
mute further warming, similar temperatures to today`s can be
expected.

MRB

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 217 AM CST Wed Nov 12 2025

Temperatures leap warmer to end the work week, coinciding with good
ensemble agreement in 850mb temperatures around the 95th
climatological percentile. Meanwhile, a strong closed low aloft
depicted uniformly among most guidance dives southeast from
central Canada, forcing a surface cyclone through the Great Lakes
region. While there`s some nominal timing differences, a majority
of ensemble members bring the front through our region late
Saturday evening. This timing leaves room for one last warm day,
now featuring more pronounced southwesterly boundary layer flow.
That resultant uptick in warm air advection, along with any
downsloping effect from the Ozarks in this flow regime and near-
record 850mb temperatures, will likely (80-90%) send temperatures
into the mid/upper 70s areawide. A new temperature record looks
elusive in St. Louis, though Columbia and Quincy have a 20-30%
chance of reaching their records according to the NBM.

Ensemble guidance continues to slow the progression of another a
closed low aloft from the Desert Southwest into the region this
weekend. While the speed of this wave remains the primary source of
uncertainty in this part of the forecast, as depicted in ensemble
EOF patterns, there is increasing confidence that the slower
solutions will come to fruition. A sluggish wave will delay more
appreciable moisture from arriving in the region by Sunday, which
will bring greater likelihood (80-90%) that the front will not
produce rain. The NBM is also catching onto this trend, now
removing mentionable rain chances altogether Sunday. High
temperatures do fall behind this front, but exactly how far is not
too certain as varying degrees of cold air advection are evident
in the ensemble guidance.

The best rain chances arrive with the closed wave Monday into
Tuesday, though there are noteworthy location and timing differences
that riddle the forecast by then. Regardless of how these
differences resolve, the threat for any impactful or hazardous
weather is fairly low. A northerly wave track would permit some
elevated instability and a few thunderstorms to develop across parts
of Missouri Monday afternoon, but that would be about the high-end
for impacts. From here on out, while details are muddy at best
surrounding precipitation and temperatures, the southwest flow
pattern that establishes will allow for multiple rain chances
through the middle of next week.

MRB

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1123 AM CST Wed Nov 12 2025

Dry/VFR conditions are forecast through Thursday morning.
Northwest winds will slacken off and go light/variable late this
afternoon/early this evening. By late Thursday morning, look for
winds to turn out of the southeast.

Gosselin

&&

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

$$

WFO LSX