Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

052
FXUS63 KLSX 232128
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
328 PM CST Fri Jan 23 2026

.KEY MESSAGES...

- A major winter storm will impact the area between Saturday
  morning and Sunday afternoon, coming in one round Saturday and a
  more widespread and significant round Saturday night into
  Sunday. The heaviest snowfall is likely to fall in southeastern
  MO/southwestern IL up to I-70.

- Bitter cold will continue through Monday, with dangerous wind
  chills expected into Saturday morning.


&&

.SHORT TERM...  (Through Sunday Night)
Issued at 320 PM CST Fri Jan 23 2026

Low-level CAA and an Arctic surface anticyclone extending into the
Mid-Mississippi River Valley has firmly established an anomalous,
bitterly cold airmass in place across the CWA with temperatures even
this afternoon around 0 to lower teens F. Persistent upper-level
clouds have also prevented many areas from warming more than a
degree or two. As a result, wind chill values have remained colder
than expected today and will only lower by tonight as temperatures
further cool. As a result, the entire CWA is now in a Cold Weather
Advisory through midday Saturday, when temperatures will rise
slightly and winds will become light. During that time, wind chill
values will rise above conventional dangerous levels but still
remain below 0 F in many locations.

A winter storm is still on track to impact the area in the Saturday
morning-through-Sunday evening timeframe with the potential to cause
significant travel impacts where heaviest amounts fall. The northern
extent of significant snowfall is still not completely clear given
the compounding uncertainties between the two rounds of the storm.
That being said, over the last 24 hours the northward shift of total
snowfall across the CWA has stabilized with a tightening northern
gradient emerging.

The first round, generated largely by low/mid-level isentropic
ascent and upper-level jet dynamics, is expected Saturday morning
through afternoon. The onset and northern extent of accumulating
snow with this first round is still quite uncertain due to the
potency of exceptionally dry, antecedent low-level air. In fact,
dewpoints this afternoon are approaching daily record minimums--
an indicator of the unusually low amount of moisture content. It
still appears that the most vigorous low-level forcing will pass
across the southern half of MO, where moistening should happen
more quickly. Therefore, there will be a gradual moistening
sufficient for snowfall gradually occurring from southwest to
northeast on Saturday, but this could cut down on snowfall
duration and totals with this first round in locations along/north
of I-70. HREF 6-hour probabilities of QPF >0.10" also taper
quickly from 60 percent south of I-70 to 30 percent north of I-70,
encapsulating the uncertainty. It is entirely possible that
portions of northeastern MO and west-central IL see no snow with
this first round. However, with very cold air and roadway
temperatures in place, even if snow is light it will efficiently
accumulate on roadways and cause impacts. There remains a
consistent signal in model guidance for a relative lull in
precipitation Saturday evening lasting for as much as 6 hours in a
minimum of large-scale forcing. Precipitation may not abate
entirely but should at least become much lighter.

Confidence remains relatively higher for the second round Saturday
night into Sunday to impact nearly the entire CWA, since large-scale
ascent will be much broader and deep/more vigorous. Model guidance
even indicates that there could be upper-level jet coupling further
amplifying ascent. However, they have varied in how multiple
shortwave troughs phase together with a longer wavelength trough,
with a trend toward a slightly less amplified solution and a less
mature cyclone with a slightly more southerly track. This makes
the intrusion of sleet along the system`s warm nose less of a
concern, but also leads to a less meridionaly elongated
precipitation shield, which could once again limit snowfall
amounts across northeastern MO and west-central IL. On the
contrary, the very end of the HREF (through 12z SUN) gives highest
confidence in 1"/hour snowfall rates across southeastern MO early
Sunday with up to 50 percent probabilities of >0.08" QPF /hour (a
lower-end reasonable proxy assuming 12:1 SLR). Accumulating snow
will gradually end from west to east Sunday midday through
afternoon as stronger large-scale ascent departs, but light
snow/flurries may linger into the evening as deeper moisture
lingers longer.

A unique aspect of this event will be the bitter cold airmass in
place, aiding in a deep, isothermal layer and elongated, saturated
DGZ, favorable for above average SLRs that could range from 12 to as
high as 20:1. However, a relatively warmer mid-level "gap" in the
DGZ will likely keep SLRs from running too high, but they will be
maximized where the strongest FGEN/ascent exists in any banding. In
terms of total snowfall, latest probabilistic snowfall data (25th to
75th percentiles) generally supports 7 to 13" in southeastern
MO/southwestern IL, 5 to 11" along the I-70 corridor, and 2 to 5" in
northeastern MO/west-central IL. However, the high end of these
ranges assumes several inches of snow falls CWA-wide with the first
round, which is uncertain per the discussion above. Lastly,
ensemble model mean total QPF has decreased in central,
northeastern MO/west-central IL and remained steady/slightly
increased elsewhere, increasing support that there could be a
rather sharp gradient in snowfall (at least between light snowfall
and significant snowfall) in those areas.

Pfahler

&&

.LONG TERM...  (Early Monday through Next Friday)
Issued at 320 PM CST Fri Jan 23 2026

Deep troughing will remain in place across eastern North America
through the rest of the forecast period. This will establish deep
northwest flow across the Mississippi Valley, though a series
shortwaves rippling through the flow will cause winds to
occasionally waver a bit more westerly than north. Ahead of each
shortwave, temperatures will warm slightly before reinforcing arctic
air rushes into the region in the wake of those disturbances.

At this point, the first additional shot of cold air will arrive on
Monday morning. This arctic air coupled with fresh snowpack will
result in bitterly cold temperatures. Even the 75th percentile of
model guidance is near or below 5 degrees areawide, which provides
high confidence that these very cold temperatures will be realized.
This, coupled with even weak winds, will push minimum wind chills to
near or below -10 in our south and to near or below -20 in our
north.

Temperatures will gradually recover during the day on Monday and
Tuesday but will still remain well below climatology. The next
shortwave will arrive around midweek, and will push temperatures
colder for the second half of the week. There is some signal that
this shortwave may have just enough moisture to work with to squeeze
out some light precipitation, though even the 90th percentile of
guidance is below 0.1" of QPF. If it does precipitate, it will be
all snow given the cold air in place, though at this point it does
not look like we`d see much more than 1" if we get anything at all.

BSH

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1137 AM CST Fri Jan 23 2026

Dry and VFR flight conditions will persist into at least early
Saturday morning with northerly winds also gradually veering to the
northeast. A winter storm will track through the region Saturday and
Sunday, coming in two rounds. The first round will arrive Saturday
morning into early afternoon, but there is uncertainty in the exact
start time of snow and associated visibility reductions given very
dry antecedent air in place. It is possible that there are periodic
visibility reductions below what is included in the current TAF.
Much of the snow will likely remain south of KUIN through 18z
Saturday. This first round will move out Saturday evening, beyond
the current TAF period, with a lull in precipitation expected.

Pfahler

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Cold Weather Advisory until noon CST Saturday 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-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Shelby MO-Warren MO-Washington MO.

     Winter Storm Warning from 9 AM Saturday to 6 PM CST Sunday for
     Audrain MO-Lincoln MO-Pike MO-Ralls MO.

     Winter Storm Warning from midnight tonight to 6 PM CST Sunday
     for Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Reynolds MO-Saint Charles MO-Saint
     Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

     Winter Weather Advisory from 9 AM Saturday to 6 PM CST Sunday
     for Knox MO-Lewis MO-Marion MO-Monroe MO-Shelby MO.

IL...Cold Weather Advisory until noon CST Saturday 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.

     Winter Storm Warning from 9 AM Saturday to 6 PM CST Sunday for
     Calhoun IL-Greene IL-Jersey IL-Macoupin IL-Montgomery IL-
     Pike IL.

     Winter Storm Warning from midnight tonight to 6 PM CST Sunday
     for Bond IL-Clinton IL-Fayette IL-Madison IL-Marion IL-
     Monroe IL-Randolph IL-Saint Clair IL-Washington IL.

     Winter Weather Advisory from 9 AM Saturday to 6 PM CST Sunday
     for Adams IL-Brown IL.

&&

$$

WFO LSX