333
FXUS63 KLSX 020246
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
946 PM CDT Sat Nov 1 2025

.UPDATE...
Issued at 940 PM CDT Sat Nov 1 2025

Fog is starting to develop north of I-70 where clouds have
cleared, and is expected to develop into mid-Missouri and the St.
Louis metro overnight as the lingering scattered clouds exit the
area. Visibilities are expected to bounce around between 1/4 to 2
miles overnight, and will linger a few hours past sunrise before
dissipating. Despite the incoming freezing temperatures and the
expected fog, warm surface temperatures will keep freezing fog
from becoming a concern.

Delia

&&

.KEY MESSAGES...

- A Freeze Warning is in effect tonight into Sunday morning as we
reach  widespread freezing temperatures for the first time this
season.

- There is a slight chance (15 - 20%) of light rain in most of the
area  this afternoon. Southeast Missouri and southwest Illinois have
  a higher chance (30 - 50%) of measurable rain with up to 0.10"
possible.

- Dry and mild conditions are forecast from Monday into late next
week.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 236 PM CDT Sat Nov 1 2025

(Analysis/Overview)

A longwave trough encompasses the eastern half of the U.S. with an
upper level low rotating southeast through the Mid-Mississippi
Valley. A weak shortwave is rounding the base of the trough,
tracking west to east, near the AR/LA border. The cold front that
passed through late last night into this morning has cleared south
of MO/IL with surface high pressure centered over the Plains.
Scattered to overcast skies accompany the shortwave and cold front
to the south, as well as the upper level low to the north. Surface
moisture drops off from southeast to northwest as the surface high
draws in drier air from the northern Plains.

(This Evening through 15z Sunday)

The upper level low is projected to parallel the Mississippi River
as it drops south over western TN around 12z Sunday morning. The
upper low incorporates very cold air aloft with temperatures at
500MB ranging from -28C to -30C and 6C-6.5C lapse rates. This has
supported isolated to widely scattered showers in an area of mid-
level saturation over northeast MO. Radar trends have shown
activity increasing since 18z and therefore raised PoPs to 30%
across much of the CWA. Showers will largely lead to trace
amounts with isolated pockets of measurable rainfall (couple
hundredths or so). The diurnally driven nature of the activity
should have it fading through sunset this evening.

It`s expected to be one of the coldest nights since last March and
April with widespread freezing temperatures affecting the bi-state
region (MO/IL) through Sunday morning. A majority of the area,
extending from Ozark Plateau through sections of west-central and
southwest IL, where 60-80% of the HREF members drop temperatures to
32 degrees or colder. This signal has become incrementally stronger
over the last few forecast cycles, leading to high confidence for
the season`s first freeze. Fog potential is an added impact, as
skies clear and the area of low/mid-level moisture settles over
central MO. HRRR guidance is rather bullish with visibilities
dropping to 1/4SM or lower along the EAX/LSX CWA border. For now, I
did not lean that heavily into lower visibilities with questions in
the extent of clouds. Trends may provide better clues to adjust
accordingly as the evening progresses.

The Freeze Watch has been upgraded to a Freeze Warning over
southeast MO and southwest IL. The same trends in HREF data to the
north have shifted slightly higher probabilities to the south.
Additional, soundings show mid-level moisture begins to decrease
after 09z tonight. Much of the guidance has nudge 1-2 degrees cooler
with lows comically landing right at 32-33 degrees in the warmer
locations. Trends were heavily favored here, along with the fact the
growing season has come to an end for many. After collaborating with
neighboring offices, the Freeze Warning was opted to hopefully mark
a definitive end to frost/freeze headlines (TBD).

(15z Sunday through 12z Monday)

Sunday remains cool with the pool of -3C mid-level airmass overhead.
The airmass begins to moderate as it moves eastward Sunday afternoon
in combination with mostly sunny skies. While temperatures remain
seasonably cool (50s), it`ll feel a little better than Saturday. Mid-
level ridging over TX will turn winds out of the west late in the
day, which will draw warmer temperatures in from the Plains. 850MB
temperatures climb by about 10C, resulting in slightly milder lows
in the low to mid-30s early Monday morning.


Maples

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 236 PM CDT Sat Nov 1 2025

(12z Sunday through 00z Monday)

The longwave trough moves east through the day Sunday with
northwesterly flow aloft, while an upper ridge stages to the west.
With the ridge to the west, we won`t see too much of a warm-up but
will tack on a few degrees over Saturday`s high temperatures with
ample sunshine. Highs return to the low to mid-50s.

(00z Monday through 12z Wednesday)

Surface high pressure shifts from central MO into western TN late
Sunday into Monday, turning winds out of the south and southwest.
Meanwhile, the upper level ridge begins to build eastward, as well,
marking the beginning of WAA and a return to near normal
temperatures (low to mid-60s). NBM`s IQR remains tightly clustered
through Monday, but then begins to spread Tuesday. Though global
guidance has come into better agreement with the synoptic pattern, a
couple minor disagreements continue to expand the spread through
Wednesday.

Global guidance shows deamplification in the upper ridge as it
progresses east late Monday into Tuesday. Another surface ridge
quickly builds southeast and eventually becomes conjoined with the
surface high over TN. The surface high building down from the
northwest follows a cold front that essentially washes out as the
upper pattern becomes more zonal and a weak shortwave rockets over
the region from west to east within the zonal upper level pattern.
This is not at all an organized, nor strong system, and the amount
of dry air around the surface ridging is expected to keep things dry
at this time. While there is some spread in the data going into
midweek, the general theme should be a modest stair step into milder
temperatures through Wednesday.

(12z Wednesday through Saturday Night)

Wednesday is favored to be the mildest day of the week, but just how
warm is still in question with spread increasing to around 7-8
degrees Wednesday afternoon. Global guidance shows a weak surface
low quickly ejecting eastward from the northern Rockies, crossing
the central U.S., along with a cold front that precedes a surface
high. Guidance diverges on both the speed and placement of these
features, which dominos on down the line from there. The boundary
lingers somewhere in the region as it gets hung up on the northwest
side of ridging over the southeastern U.S. Exactly how this plays
out is less certain at this distance in time, but the placement
could result in anything from seasonably cool temperatures to above
normal temperatures with 10-12 degrees separating the 25th/75th
percentiles in the NBM data. Yet another system approaches late
Thursday into Friday, potentially bring a round of showers along
another cold front Friday. Given the spread that develops by
midweek, confidence in the late week isn`t any greater at this time.


Maples

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 625 PM CDT Sat Nov 1 2025

Light rain showers continue across the St. Louis metro area but
will diminish in the first few hours of the TAF period, leaving
dry conditions for the remainder of the forecast. Clouds will
continue to clear from northwest to southeast across the area,
leaving the mid-Missouri terminals (KJEF, KCOU) and KUIN under a
clear sky overnight. Fog is expected to result, bouncing between
2SM and 1/2SM over the early morning hours. Fog will eventually
mix out during the morning, but now that we`ve entered the cool
season, will take a few hours longer than we were used to.

The St. Louis metro is not expected to clear out as quickly. But
if it does clear withing the first few hours past midnight, IFR fog
will be a concern at KSUS and KCPS. We`ll continue to monitor this
potential through the evening.

Northwesterly winds will become light and variable as a surface
high moves across the area overnight. Winds will pick up from the
southwest late in the day Sunday.

Delia

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Freeze Warning from 1 AM to 7 AM CDT Sunday for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Sainte Genevieve MO-Shelby MO-Warren MO-Washington MO.

     Frost Advisory from 1 AM to 7 AM CDT Sunday for Saint Louis City
     MO-Saint Louis MO.

IL...Freeze Warning from 1 AM to 7 AM CDT Sunday for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX