622
FXUS63 KLSX 011122
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
622 AM CDT Sat Nov 1 2025

.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 Afternoon)
Issued at 308 AM CDT Sat Nov 1 2025

As of 0530z, surface analysis shows a cold front just southeast of
our CWA. Very light rain has followed in south-central Missouri
along its 850 mb front, but dry air near the surface has evaporated
most of it before it`s reached the ground. Rain will continue east
this morning, with front remaining in the vicinity of our
southeastern border. The coverage of rain along the front will
increase through the late morning as greater forcing associated with
an upper level closed low dives into the Mid-Mississippi Valley.
Portions of far southeast Missouri and southwest Illinois will be
the only beneficiaries of this increased rain, though amounts will
still be low. 00z HREF probabilities of 0.10" of rain only peak
at 40%. Behind the front, steep low-level lapse rates caused by
cold air advection will result in meager instability. Though the
chances of any one location being hit is low, there is enough of a
chance of isolated to scattered showers behind the front to
warrant mention. Some lucky few will likely see light rain
associated with them.

The aforementioned cold air advection along with persistent cloud
cover will severely stunt the diurnal temperature trend today. As
opposed to widespread highs in the 50s like we`ve been seeing,
today most locations north of I-70 will struggle to hit 50 at all.
Even our warmest locations have a 90% chance at failing to reach
55 degrees.

Perhaps more notable will be our temperatures tonight. Surface high
pressure will settle into the Mid-Mississippi Valley tonight,
scouring out remaining cloud cover, calming winds, and allowing
radiational cooling to take place. The NBM has been cooling its low
temperature forecast for tonight over the past few days, which is on
par given its warm bias in radiational cooling events. This bias can
be seen in the NBM`s forecast vs its 25th/75th IQR spread, in that
its forecast is consistently higher than its 75th percentile lows at
numerous sites in the CWA for tonight. This is relevant considering
that these warm forecasts are still at or below freezing. This,
along with the environmental conditions in place tonight, yield high
confidence in a widespread freeze. Thus, our Freeze Watch has been
upgraded to a Freeze Warning for the majority of the CWA. A small
portion of eastern Missouri including St. Louis City and County and
our southwest Illinois counties continue to be in a Freeze Watch for
the time being. With the exception of St. Louis where the urban heat
island has the most influence, there is uncertainty regarding how
quickly remnant cloud cover clears and how low dewpoints will fall
throughout the night. If they don`t fall under 32 degrees, our
temperatures by definition cannot either. According to the 00z HREF,
these locations have about a 50/50 chance at dewpoints reaching 32
degrees, which, along with the possibility of cloud cover, yields
too much uncertainty to upgrade to a Warning at this time.

Jaja

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 308 AM CDT Sat Nov 1 2025

The upper level trough will exit the region on Sunday, with ridging
building in behind it. This and low-level southwest flow will open
us up to warm air advection and allow our temperatures to moderate
back into the 60s by Monday. The pattern through next week is fairly
dynamic, with two ridges and two cold fronts passing by late week.
The shortwaves will push weak cold fronts through the Mid-
Mississippi Valley on Monday and again on Wednesday, but a dry
column and weak post-frontal airmasses will make fleeting cloud
cover the most noticeable impact from each passage. A stronger
trough will threaten to bring the chance of showers back into the
forecast along a cold front late next week, but variability in
guidance makes it difficult to expound on the details at this
juncture.

Jaja

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 603 AM CDT Sat Nov 1 2025

Winds will continue to veer to northwesterly today behind a cold
front that has cleared the area. In southwest Illinois and
southeast Missouri showers will increase in coverage through early
this afternoon before exiting the CWA to the east. Areawide,
isolated to scattered showers are possible within a field of
post-frontal stratocu. No impacts are expected from today`s
showers.

Confidence is increasing that fog, perhaps dense at times, will
develop across much of the area, namely in locations under a
Freeze Warning. The combination of fog and below freezing
temperatures may result in spots of freezing fog, but confidence
in this occurring specifically is low at this time. Will continue
to monitor as new guidance comes in today.

Jaja

&&

.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-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-Shelby MO-
     Warren MO-Washington MO.

     Freeze Watch from late tonight through Sunday morning for
     Jefferson MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO.

IL...Freeze Warning from 1 AM to 7 AM CDT Sunday for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin
     IL-Madison IL-Montgomery IL-Pike IL.

     Freeze Watch from late tonight through Sunday morning for
     Clinton IL-Marion IL-Monroe IL-Randolph IL-Saint Clair IL-
     Washington IL.

&&

$$

WFO LSX