117
FXUS63 KLSX 131116
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
516 AM CST Thu Nov 13 2025

.KEY MESSAGES...

- Unseasonable warmth continues to build today, peaking Friday
  through Saturday when high temperatures will threaten records.

- Our warm, dry stretch is poised to end next week, though exactly
  how that will manifest remains uncertain.

&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 227 AM CST Thu Nov 13 2025

A surface high evident on regional analysis is drifting further
southeast from the Mid-Mississippi Valley, with heights aloft
gradually rising and low-level winds veering southerly. All of
this points to a warm advection bolstering our unseasonable
warmth across the region. While high-resolution guidance hints at
some degree of cloud cover, primarily across the southern half of
Missouri, there isn`t much to support more than translucent
cirrus or cirrostratus that won`t suppress warming notably. The
warmest temperatures will be observed in central and northeast
Missouri, where downsloping from the Ozarks will give a slight
boost to temperatures. Further east, the more southeasterly wind
direction will still maintain low to mid-60s highs, but there`s
little to suggest much more than that in the guidance.

As discussed at length in previous forecasts, temperatures take
another leap tomorrow with a stronger LLJ drawing warmer air into
the region. The southwesterly surface flow depicted in nearly all
available guidance also favors downslope warming from the Ozarks.
With sustained wind speeds jumping to 10-15mph amidst a
strengthening surface pressure gradient, that downslope effect may
stretch as far north and east as the St. Louis metro area. The
result is a 5-10 degree temperature increase compared to today`s
highs. While southwesterly flow typically dries us out in the low-
levels, the moisture return in this scenario is much more
uninterrupted in even the driest of ensemble output. Current
dewpoints are forecast in the upper 50s to near 60 degrees, which
will be noticeably more humid than days past. This lines up with
the average last time we observe such values for a given calendar
year, according to local climatology.

MRB

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 227 AM CST Thu Nov 13 2025

Despite strengthening pre-frontal southwesterly surface winds and
850mb temperatures consistently modeled in the 99th climatological
percentile by ensembles, temperatures Saturday now look more
likely to plateau compared to Friday rather than warm further. As
previously discussed, the favorable conditions for record warmth
have the potential to be thwarted by increased cloud cover. This
detail not only stifles insolation and surface warming, it also
dampens low-level mixing heights which would keep us from fully
realizing the near-record 850mb temperatures. In addition to these
aspects to the forecast, the timing of the front is not set in
stone. A few deterministic models have FROPA occurring as early as
noon in our north, which would further stunt warming. As such,
the records at St. Louis (81F), Columbia, MO (78F), and Quincy, IL
(75F) look safe by a degree or two at the very least on Saturday.

The front is uniformly shown to not only exit the bi-state region by
sunrise on Sunday, but to be dry as it does so. It is becoming a
more realistic possibility that, while much cooler (upwards of 15
degrees cooler per the NBM) temperatures will arrive in its wake,
much drier air will take hold as well. If cold air lags behind the
dry air *just* right, we may see instances of elevated fire danger
despite relatively weak surface winds. GEFS/EPS RH output is
impressively low for this lead time, with cluster analysis showing a
potential for widespread low-20s RH values. That said, that scenario
is heavily dominated by the GEFS which has a known dry bias due
to unrealistically-deep mixing. The deterministic NBM, often
having the opposite issue with dewpoints being too warm, is
surprisingly dry and paints 20-30% RH values for us. While far
from certain, there is at least a 30-40% chance for erratic fire
spread Sunday.

The forecast period from Monday onward is still fraught with
uncertainty, largely surrounding the amplitude of a wave that ejects
east from a longerwave trough aloft over the Southwest CONUS. While
EOF patterns still illustrate this source of uncertainty in the
ensemble guidance, it is lower than previous forecasts and leaning
towards a weaker, quicker, more southerly track to the wave. This
would still bring our dry spell to an end, but keep any impacts
beyond that at bay. The NBM 90th percentile for 24-hr precipitation
(think near the worst-case) is 0.50-1.00 inches with the highest
totals near the Mississippi River. With drought ongoing and little
in the way of available instability to bring convective downpours, I
have little doubt that this would be beneficial rain at best. By
Tuesday, while this wave will be departing, what happens next is far
from certain. Ensemble guidance depict upper-level flow patterns
that range from quasi-zonal to deeply-amplified, which have
implications on our precipitation and temperature forecast. The NBM
high temperature interquartile range for Tuesday is a laughable 25-
30 degrees. The pattern remains active and unsettled through the
remainder of the forecast period, but rain chances are non-zero no
matter which depiction is correct.

MRB

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 512 AM CST Thu Nov 13 2025

Dry, VFR conditions will continue through the TAF period. Winds
will strengthen today out of the south/southeast before weakening
overnight. The only item of some concern surround the low-end
threat for low-level wind shear overnight tonight. A strong LLJ
will develop overhead, though the shear itself seems gradual and
perhaps more indicative of mechanical turbulence. LLWS was kept
out of the TAF for now, but this possibility will be monitored.

MRB

&&

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

$$

WFO LSX