535
FXUS63 KLSX 131127
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
627 AM CDT Mon Oct 13 2025

.KEY MESSAGES...

- Near to above normal temperatures hold through at least Friday. A
  cold front brings progressively cooler air through the weekend.

- A majority of the week remains rain-free through Friday afternoon.
  Rain chances increase Friday night into Saturday (50-60%).


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 320 AM CDT Mon Oct 13 2025

The narrow corridor of ridging that maintained mostly clear skies
yesterday has shifted east and now extends from the Great Lakes
through the Ohio and Tennessee Valleys into the northern Gulf. The
elongated ridge is hugged by trough to its east and west. The
eastward shift in the synoptic pattern has allowed the western ridge
to lean far enough east to bring clouds and a few showers to parts
of the region late last evening into this morning.

IR satellite shows broken cloud cover as far east as the Illinois
and Indian border with radar mosaics plotting showers from west-
central Illinois through central and southwest Missouri. A weak
surface low over eastern Kansas is making a play on the stalled
boundary, returning it north as a weak warm front. The warm front
marks the divide between temperatures in the upper 50s/near 60
degrees and upper 60s/low-70s from central Missouri westward. Drier
air (dewpoints in the 40s) to the east gives way to relatively moist
air (dewpoints near 60 degrees) to the west. These elements will be
the primary factors in today`s forecast.

The weak surface disturbance shows little movement as it is
suppressed by another surface ridge building in from the northern
Plains. Additionally, the lack of upper ascent and dry, more stable
air to the east will impeded the eastward extend of showers this
morning. Probabilities (15-40%) for showers will continue to
decrease through late morning.

The biggest change in the last 24 hours is the adjustment in high
temperatures. Thicker cloud cover lingers over central Missouri into
sections of west-central Illinois as moisture is fed northeastward
and increasing wrapped around the mid-level ridge with time. Thicker
cloud cover keeps temperatures 3-5 degrees cooler (mid-70s) over
central Missouri. To the north and south, clouds give way to a
little more sunshine with highs in the upper 70s to low-80s. Clouds
are stubborn to move as the mid-level pattern is nearly parked
overhead. This keep the northwest quadrant of the CWA milder (low-
60s) with mid to upper 50s under mostly clear/partly cloudy skies in
southeast Missouri through southwest Illinois.

Tuesday brings a modest warming trend with a return to widespread
low-80s with clearing. As the surface ridge builds in from central
Plains, easterly surface flow around the eastern side of the ridge
pushes drier air from east to west. HREF temperatures spreads (due
to questions with cloud cover) have decreased across the north,
leaning into the warmer solutions that will bring upper 70s as far
north as Quincy, while the cooler (low-70s) shift toward the Iowa
and Missouri border.


Maples

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 320 AM CDT Mon Oct 13 2025

Upper level longwave ridging continues to steer the active weather
through the Plains and northern CONUS late Tuesday through Friday.
Meanwhile, guidance shows mid-level moisture continuing to eject out
of the southwest and wrapping around and into the ridge. This
initially makes a small, but noteworthy play on temperatures over
the northern sections of the CWA Wednesday with upper 70s extending
across northern Missouri into central Illinois. Conditions remain
dry with gradual warming Thursday with more sunshine.

The upper ridging pattern begins to show signs of change late
Wednesday into Thursday, losing some amplitude and shifting east of
the region by Friday. A longwave trough shifts east in tandem as an
upper low ejects out of the Intermountain West into Canada.
Southwesterly flow strengthens through the day Friday, drawing 15-
20C H8 air in from the southern Plains in what is likely to be the
warmest day of the week (low/mid-80s).

The long-awaited question is the rainfall potential considering how
dry is has been in recent weeks. Ensemble data remains fairly well
clustered through the day Friday before diverging Saturday into
Sunday. Guidance is in better agreement than previous days, but
timing issues remain. General consensus bring the cold front into
the region late Friday night into early Saturday morning, then
quickly moves it southeast Sunday morning. This mainly impacts the
start and end times of measurable precipitation with blending
between guidance likely too dispersive. Per usual, this is likely to
be fine-tuned in coming days with better consensus among the
ensembles as medium range guidance can better resolve potential vort
lobe rotating around the parent upper level low and over top the
surface boundary.

As of now, trends are looking a little more favorable for rainfall,
but it is more likely to be a progressive hit rather than a long
duration, soaking that we need. Through much of the week, the
moisture source out of the Pacific (uncommon) is cutoff,
transitioning to the western Gulf. One key is how quickly we can
transition to Gulf moisture as the front advances from the
northwest. Fortunately, long range deterministic solutions show
strong moisture advection drawing 60 degree dewpoints into the mid-
Mississippi Valley ahead of the front. Additionally, we may finally
have a low level jet to work in light of the tightening pressure
gradient. If current trends stick, we may be able to squeeze out a
reasonable amount of rainfall to hold use over for a few days. LREF
guidance shows 50-70% probabilities for measurable rainfall lining
the front Saturday morning through Sunday morning. Amounts are
dispersed roughly between 0.25" to 1" in the interquartile range
(25th-75th percentile).

While these aren`t impressive numbers that would put a dent in
drought conditions, the pattern may become more active and cooler
beyond the end of the long range period. It might be the first step
to additional chances further out. Cooler, more seasonal
temperatures follow (mid-60s/low-70s).


Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 619 AM CDT Mon Oct 13 2025

Light rain continues to line up from northeast Missouri through
central Missouri early this morning. Rain is falling from mid-
level cloud bases that is running into drier air and high pressure
to the east, which will limit potential to central Missouri
terminals (KCOU/KJEF) and KUIN. Not much impact is expected
considering the light nature of the precipitation. What currently
exists is expected to fade through mid to late morning.

VFR conditions are expected to continue otherwise. There are
indications that a brief stint of patchy fog is possible over
central sections of Missouri late tonight into early Tuesday
morning. This was not included in this TAF package as the
potential may be able to be handled with TEMPO groups in later
updates.

Maples

&&

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

$$

WFO LSX