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FXUS63 KLSX 161123
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
523 AM CST Sun Nov 16 2025

.KEY MESSAGES...

- Seasonably mild and dry conditions are expected today.

- A round of showers and a few thunderstorms is very likely
  (50-80%) late Monday through early Tuesday. Some small hail is
  possible with the stronger cores.

- Widespread rain is nearly certain (90+%) at some point between
  Wednesday and Friday, with multiple rounds possible. Uncertainty
  remains high regarding specific timing, amounts, and locations,
  but substantial, soaking rain is likely in some areas.


&&

.SHORT TERM... (Through Late Sunday Afternoon)
Issued at 225 AM CST Sun Nov 16 2025

After another warm and breezy day today, a dry cold front has
ushered in a more seasonable and very dry airmass, along with
surface high pressure and light winds. This is expected to persist
throughout the day, with generally benign sensible weather as a
result. Temperatures are expected to reach near or slightly above
seasonal averages in the mid 50s to mid 60s, with light winds and
only a few passing high clouds.

The most notable aspect of today`s weather will actually be the
degree of dryness, as surface dewpoints are expected to drop into
the teens and 20s. This is likely to produce very low afternoon
humidity, likely reaching near 20% and potentially even lower in a
few spots. This would ordinarily be cause for concern for outdoor
burning activities, but fortunately high pressure will keep wind
speeds prohibitively light aside from a few northerly gusts in the
10 to 15 mph range across parts of Illinois.

Overnight, the combination of very light winds, mostly clear skies,
and low dewpoints will lead to ideal conditions for radiative
cooling. Expect temperatures to drop into the 30s in most areas,
with a brief freeze possible mainly in rural areas east of the
Mississippi River.

BRC

&&

.LONG TERM... (Monday through Saturday)
Issued at 225 AM CST Sun Nov 16 2025

After a quiet start to the week, a much more active pattern will
unfold Monday through Friday, with multiple rounds of showers, a few
thunderstorms, and potentially substantial rain totals.

(Monday - Tuesday)

While much of the day Monday will remain dry, a weakening but still
potent shortwave will move through the central Plains and approach
the mid-Mississippi River valley. Beginning late afternoon and
continuing through the evening/overnight, a robust low level jet
will overrun cool, stable low level air, and the combination of
isentropic ascent and convergence along the nose of this feature
is very likely (50 to 80%) to produce widespread showers,
especially across far eastern Missouri and much of
southern/western Illinois. Not only this, but model guidance
continues to forecast moderate elevated instability (500 to 1000
J/kg), along with substantial effective wind shear within the
storm layer (at least 40 kt and likely more). While storms are
very likely to remain elevated overnight Monday, it would not be
surprising to see a few bouts of small hail or even some brief
gusty winds within the stronger cores.

As Tuesday morning approaches, model guidance suggests that warm air
advection will begin to erode the stable boundary layer in areas
south of I-70, and frontogenesis will result in a tightening, nearly
stationary warm front. This will occur ahead of the advancing
surface low and shortwave, which will sweep through the area during
the day. While there remains some uncertainty in the timing and
track of these features, this is painting a clearer picture of
Tuesday`s weather conditions, which will likely feature a wide range
of temperatures from north to south thanks to the stalled front, and
perhaps a lingering chance for a few showers or thunderstorms.
Ensemble precipitation probabilities remain somewhat low after
sunrise Tuesday, but given the lingering boundary and a few
deterministic solutions that produce a smattering of late
morning/early afternoon convective showers, Tuesday may not be
entirely dry. Meanwhile, this also leaves the door slightly open for
a few surface-based thunderstorms as well. Precipitation remains
likely to clear out by early Wednesday behind the passing trough, as
the surface boundary gets shunted slightly southward. Still, it is
likely to stall somewhere near the Arkansas border, and will remain
a player in the weather conditions in subsequent days.

(Wednesday-Friday)

Between Wednesday and Friday, confidence continues to increase that
widespread rainfall will occur across the area, potentially in
multiple rounds. At this point, while there is still quite a bit of
variability in the timing/location/amounts of heaviest rain, it is
nearly certain (90% or higher) that at least some rain will fall
across essentially the entire area at some point within that window,
with a steadily increasing chance for more substantial, soaking rain
as well.

The primary driver of this wet pattern will be another, more
substantial shortwave trough that is expected to slowly emerge into
the central/southern plains Thursday and into the mid-Mississippi
River valley on Friday. Ahead of this trough, steadily increasing
deep southwesterly flow will produce persistent isentropic ascent
above the stalled surface front Wednesday and Thursday. Likewise,
anomalously rich moisture will also stream into the area, with
ensemble mean precipitable water values exceeding the 90th
percentile. As a result, light/moderate shower coverage is expected
to gradually increase along the boundary, and while the initial
activity may be focused to our south Wednesday through early
Thursday, at least some of this activity is likely to move into the
southern half of our area Wednesday through Thursday morning.

Sometime afterwards on Thursday, a deepening surface cyclone will
approach the area from the central plains, and likely dramatically
increase the southerly flow and isentropic ascent as it does.
Precipitation is also expected to intensify and spread north and
east in response, and eventually move across our entire forecast
area between late Thursday and late Friday. Exactly when this occurs
and where the axis of heaviest rain traverses is probably the
biggest lingering uncertainty with this forecast. While initial
ensemble data suggested (and largely still does) that the heaviest
rain is most likely to fall across the Ozarks thanks to the
potential for multiple rounds, there remains considerable
variability in the low track Thursday/Friday. This is leading to a
high degree of variance among LREF clusters, with some keeping the
heaviest rain across mainly the Ozarks and southern Illinois, while
two others pull this heavier rain much farther north as the low
deepens, with a more meridional (N/S) orientation as well. Long
story short, some areas are going to get a soaking, but it`s not
entirely clear exactly where just yet.

When it comes to amounts, the ensemble probabilities remain largely
unchanged, albeit we do note a very slight increase overall, and a
continued northward shift. NBM probabilities of 1 inch of rain or
more are now at least 40% everywhere, and as high as 80% south of I-
70. This decreases to between 40 and 50% south of I-70, with a much
sharper dropoff farther north. Meanwhile, 90th percentile amounts
have crept into the 3 to 4 inch range, with much higher amounts
farther south across Arkansas where forecast totals have been
consistently higher. All of this paints a picture of a soaking,
largely beneficial rain event, with a lower (but non-trivial) chance
for localized heavy rain and more noticeable impacts.

Meanwhile, we will also need to keep an eye on the potential for
thunderstorms Thursday and possibly Friday as increasing warm air
advection carries a more unstable airmass northward and forcing
increases ahead of the approaching trough. It`s difficult to
envision substantial instability developing after such persistent
precipitation and cloud cover, but given the strong dynamics and
just enough model instability, it`s something that will need to be
monitored as well.

(Weekend)

Precipitation chances decrease Saturday and Sunday as the shortwave
moves out of the area, and ensemble guidance suggests a modest
cooling trend as well. There are also hints of additional rounds of
precipitation as we near the end of the weekend and early next week,
but overall probabilities are low and ensemble spread is very high
regarding the next approaching trough.

BRC

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 522 AM CST Sun Nov 16 2025

VFR conditions are expected throughout the 12Z TAf period, with
light winds and only a few passing high clouds. Breezier southeast
winds are expected tomorrow afternoon, but this is just beyond
this TAF period.

BRC

&&

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

$$

WFO LSX