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FXUS63 KLSX 122304
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
604 PM CDT Sun Oct 12 2025

.KEY MESSAGES...

- Near to above normal temperatures stay in place through the
upcoming week.

- Mostly dry conditions are expected until the upcoming weekend,
when the best chances (40-50%) of appreciable rain arrive.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 150 PM CDT Sun Oct 12 2025

Between two amplified upper-level troughs, one centered across the
Northwest U.S. and the other stalled along the eastern seaboard
under a larger ridge, high surface pressure and dry conditions
persist in the Mid-Mississippi Valley. Southerly winds are beginning
to strengthen across western and central Missouri in advance of a
slowly-advancing cold front currently draped across the northern
Plains. The continued southerly flow is keeping temperatures
slightly above mid-October normals, while gradually drawing low-
level moisture poleward. The front is still forecast to approach the
region overnight tonight, but all indications are that the upper-
level support will stay north of us. Without the upper-level wave,
the front will stall and weaken drastically in northern Missouri and
west-central Illinois.

For most in central/northeast Missouri and west-central Illinois,
the only impact will be increased cloud cover that help keep lows a
few degrees warmer than last night. A few sprinkles or periods of
light rain are possible, but the lack of mid-level lift, weak low-
level forcing from the front, and absent low-level jet will make any
appreciable rain very hard to come by. Further south and east, skies
will be clear most of the night and no impacts from the front are
expected. The clear skies will likely result in another night of
efficient radiational cooling in these areas, causing river valley
fog that will be locally-dense. Fog will gradually dissipate by
around sunrise as clouds continue to progress east, and by mid-
morning diurnal mixing will scour out any lingering visibility
restrictions. If the front still exist by then, it will be north of
the forecast area and abnormal warmth will persist for Columbus Day.
The one change will be lingering cloud cover, which will stunt
further warming for most of the region.

MRB

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 150 PM CDT Sun Oct 12 2025

All available guidance continues to depict a building ridge aloft
from Tuesday onward, setting up what can only be described as a
summer-like pattern in mid-October. Temperatures do cool into the
low 70s in the northern tier of Missouri and western Illinois
Tuesday into Wednesday thanks to a cool northeasterly wind on the
backside of a surface ridge over the Great Lakes. Further south,
easterly to southeasterly winds combined with rising heights aloft,
will keep temperatures in the upper 70s to low 80s. This warm and
dry pattern continues on through the week, and while it will make
for nothing short of a fantastic week to be outside, it is not
welcomed news to those with drought or fire weather interests. The
saving grace for the latter group is a general lack of sustained
wind above 10-12mph until at least Friday. If there is any threat of
warm, dry, and windy conditions, it would be Friday.

We continue to eye the upcoming weekend as the next best chance for
beneficial rain. By then, a more amplified trough-ridge pattern will
materialize over the CONUS. The resultant deep southwest flow aloft
is a favorable synoptic pattern for more active sensible weather.
For this reason, the CIPS Extended Analog guidance from Saint Louis
University, which relies on large-scale pattern recognition, is very
bullish on above-normal rainfall for the bi-state region. As one
drills down into the full ensemble envelope, however, there are
important timing and amplitude differences in the pattern that will
affect the amount and areal extent of the rain. There is a good deal
of confidence that we`ll see a front drop through the region, and
much of the ensemble guidance does paint some higher integrated
water vapor transport along that front. The combination of those two
leads to a promising recipe for rain, but how the cyclone itself
evolves will be an important factor.

If the wave is less amplified and quicker, the surface low may stay
further north and widespread rain will be harder to achieve. The
slower, more amplified solution brings more forcing (and rain) to
the region. This scenario may also allow for a second round of rain
to end the weekend, but most solutions do not suggest that. It`s
also important to keep in mind that existing drought may adversely
impact the low-level moisture profile in the quicker, weaker
scenario. While this feature represents our best chance for
widespread rain in the last few weeks, we`re far from certain on
how beneficial it will be.

MRB

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 541 PM CDT Sun Oct 12 2025

River fog with MVFR (possible IFR) conditions are expected to
develop late tonight at SUS, with lesser chances at CPS and JEF.
Light showers are expected to develop over western Missouri
tonight, but the chances of them moving into UIN/JEF/COU continue
to be too low to include in the TAF. Otherwise, dry and VFR
conditions are expected with winds staying under 10 knots.

Britt

&&

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

$$

WFO LSX