549
FXUS63 KLSX 051055
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
555 AM CDT Sun Oct 5 2025

.KEY MESSAGES...

-High temperatures in the 80s will persist today and Monday.

-There is a 40-60% chance for rain across the forecast area Monday
into Tuesday, though not everyone will see rain.

-Temperatures will cool briefly to near normal Wednesday and
Thursday.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 314 AM CDT Sun Oct 5 2025

Morning satellite imagery shows our next weather system over the
Dakotas and Nebraska, associated with a strong mid-level trough
along the US-Canada border. Imagery also shows a mid-level ridge
persists over the Eastern Seaboard. The strong ridge combined with
an exiting surface high are resulting in clear and dry conditions
across the mid-Mississippi Valley again today. Deep mixing and
southerly low-level winds will support high temperatures a few
degrees warmer today than yesterday. The deep mixing will also bring
gusty winds to the surface, particularly across northeast Missouri
and west-central Illinois, closest to the low-level jet. Winds will
gust during the afternoon into the low 20s (mph), diminishing with
sunset.

The mid-level trough will push eastward Sunday and Monday,
approaching the mid-Mississippi Valley. As this feature edges the
mid-level ridge to the east, a shortwave disturbance will flow north
through the ridge from the Southeast into the mid-Mississippi Valley
during the day Monday. This will bring chances for showers and
thunderstorms back to portions of southeast Missouri and southern
Illinois Monday afternoon and overnight. Global ensemble guidances
indicates a 40% chance for at least 0.25" and a 25% chance for at
least 0.50" across southeast Missouri. And hi-res ensemble guidance
indicates a 50-60% chance that at least 0.10" will occur as far
north as the I-44 corridor. This increases confidence that at least
some folks will see some minor relief from our most recent dry
spell, though not everyone will benefit from this rain due to its
convective nature.

At the same time a cold front will approach the region from the
northwest, driven by the approach of the mid-level trough. The front
is expected to enter the CWA Monday evening, and progress through
the area Tuesday. The front won`t be particularly strong when it
enters the CWA and will rapidly lose its low-level forcing and
surface convergence as it moves into the CWA. There is only a 50-60%
chance of 0.10" of rain across northeast Missouri and west-central
Illinois, and only a 25% chance of 0.25" in the same area.
Probabilities of these rainfall amounts drop off rapidly as it moves
southeast through the CWA. Once again, not everyone will see rain,
and even those who do are not expected to see a beneficial rain.
High temperatures on Monday will be in the mid 80s ahead of the
front, temperatures will be stunted several degrees where rain
occurs in the afternoon.

Delia

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 314 AM CDT Sun Oct 5 2025

The cold front will continue to slide through the forecast area
Tuesday as the axis of the mid-level trough pushes across the CWA.
Behind this front, a surface high pressure will move into the region
while a mid-level ridge slides in behind the exiting mid-level
trough. The result will be the advection of cool, dry continental
air into the mid-Mississippi Valley. Cooler temperatures are
expected in the wake of the front as 850 temperatures drop to 8-10C,
and confidence is high that temperatures will hit their peak closer
to normal for this time of year, solidly in the 70s. These seasonal
temperatures will last at least through Thursday under the influence
of easterly low-level and surface winds.

By Friday the mid-level pattern starts to diverge, with the ensemble
guidance evenly split in how to evolve the mid-level ridge. One
scenario shows the ridge strengthening across the central US and
remaining in place through much of the rest of the forecast. This
scenario would support a return to well above normal temperatures.
Scenario two indicates the ridge retrograding to the Intermountain
West and strengthening there, resulting in northwesterly flow over
the mid-Mississippi Valley and near normal temperatures. In a period
fraught with uncertainty, a largely dry forecast is the unifying
factor between these scenarios. While there are some periods that do
show PoPs (Friday), confidence in this occurring is low due to the
uncertainty in the evolution of the mid-levels and the lack of
moisture return into the region from the Gulf.

Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 553 AM CDT Sun Oct 5 2025

Fog has developed at KCPS overnight, and is also expected to
develop at KSUS before 13Z. Conditions will continue to bounce
across flight category until dissipating around sunrise.
Otherwise, dry and VFR flight conditions will continue through the
remainder of the TAF period. Winds will come from the south,
becoming gusty during the late morning into afternoon, reaching
the upper teens to low twenties. Gusts will diminish with sunset.

Delia

&&

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

$$

WFO LSX