986
FXUS63 KLSX 111115
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
515 AM CST Tue Nov 11 2025

.KEY MESSAGES...

- Warmer weather returns today, along with gusty winds as strong
  as 25-35mph during the afternoon.

- Abnormal warmth lasts through the rest of the week, reaching
  the 70s by Friday and coming within a few degrees of high
  temperature records Saturday. Rain chances are virtually zero
  until the weekend.

&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 327 AM CST Tue Nov 11 2025

The pronounced, anomalous upper-level low and surface ridge that
brought the Mid-Mississippi Valley its first taste of winter for
the season are now east and south of the region, respectively. In
their wake, strong southwest return flow from the surface to 850mb
is resulting in a potent wing of warm air advection through this
layer. Further up aloft, a thick cirrus deck stretching as far
north as North Dakota is drifting south and east amidst the
northwest upper- level flow and enveloping the region.

Despite the strong warm advection aloft, the abundant cloud cover
that is likely to persist through at least the early afternoon (per
RH progs and model soundings) will inhibit insolation. As a result,
surface temperatures will be stunted a bit and low-level mixing will
struggle to tap into the very warm 850mb air. Temperatures today
will still reach the mid/upper 50s, 10-15 degrees warmer than
Monday`s highs amidst a gusty southwest wind, marking the start of a
warming trend through the rest of the week. These southwest surface
winds are also forecast to draw Gulf moisture very gradually into
the region, though guidance is probably depicting this surge too
aggressively per usual in these flow regimes. As a result, despite
the muted warming due to cloud cover, minimum RH values are still
forecast on the lower end of the ensemble spectrum (low/mid-30s
areawide) amidst strengthening gradient winds. While these factors
do combine to produce instances of elevated fire danger, the stunted
mixing and cloud cover will likely keep any tangible threat
localized and marginal. Please refer to the Fire Weather Forecast
(FWFLSX) for a more technical discussion on this threat.

Weak shortwaves embedded in the northwest flow aloft will force a
weak surface low and equally-unimpressive cold front through the
Upper Mississippi Valley overnight tonight. The front barely reaches
the bi-state region before stalling and drifting back north,
according to nearly all available short-range guidance, so no
sensible impacts can be expected. Despite a west/west-northwest wind
direction on Wednesday because of this dry front, temperatures will
be bolstered by deeper mixing to tap into the warmer air aloft.
Highs on Wednesday are likely (80% chance) to jump another 5 or so
degrees compared to today`s.

MRB

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 327 AM CST Tue Nov 11 2025

Dry and unseasonably-warm conditions continue Thursday with,
the high temperature interquartile range (IQR) only marginally
warmer compared to the day prior. Despite upper-level heights
gradually rising, low-level winds are fairly weak and not promoting
any warm advection of note. That changes Friday with deeper
southwest flow returning to the region, as depicted in a
preponderance of ensemble members and deterministic models. Warm air
advection throughout the boundary layer becomes more pronounced and
850mb temperatures near the 97th climatological percentile are
depicted by ensemble guidance. As a result, temperatures jump
several degrees to close the work week. By then, NBM probabilities
of high temperatures of at least 70 degrees are over 60% nearly
areawide, and essentially 100% along and south of I-70. That said,
Saturday really looks like the warmest day of the forecast period
(and possible for some time after that) under more widespread
anomalous 850mb temperatures and a stronger southwest wind near the
surface.

That amplified boundary layer flow will develop as the result of a
mid-level shortwave and surface low tracking east across the
northern CONUS, which drags a cold front through the Midwest late
Saturday night into Sunday. Earlier forecasts suggested a faster,
more progressive wave pattern that allowed a cutoff low aloft in the
Desert Southwest to interact with this front and draw moisture
poleward. There is now a gradual but important trend to slow this
feature down, which would in turn lend less upper-level support and
low-level moisture to the approaching cold front. Rain chances are
beginning to shift later in the weekend as a result, with Sunday now
having higher chances of staying dry amidst the frontal passage.
That said, the NBM PoPs were used, owing to the uncertainty that
litters this aspect of the forecast. Rain chances now look higher
early next week in the deterministic guidance and most ensemble
members, when the cutoff low finally arrives.

Any details surrounding rainfall timing and location, along with any
threat for strong to severe thunderstorms that is being advertised
by some AI-based guidance, should be taken with a large grain of
salt, especially with the ensemble EOF patterns showing the timing
of this cutoff wave being a huge source of uncertainty in the
forecast. What does appear at least somewhat certain is that
temperatures will moderate from their near-record values on
Saturday, but with IQRs upwards of 20 degrees by early next week,
exactly how cool we get is anyone`s guess at this stage. It will
likely come down to any ongoing precipitation and cloud cover, which
is all tied to the uncertainty discussed earlier.

MRB

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 457 AM CST Tue Nov 11 2025

Dry and VFR conditions will continue across the region through
Wednesday morning. The main aviation concern will be the
strengthening southwest winds with gusts to 25-30kts later this
morning through the afternoon. While impacts will be minor most of
the time, I can`t rule out some periodic crosswind impacts on
NW/SE oriented runways during the peak mixing of the afternoon.
Any concerns will abate around sunset, when winds weaken notably
and remain that way through the remainder of the period.

MRB

&&

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

$$

WFO LSX