Area Forecast Discussion
675
FXUS63 KLSX 182332
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
532 PM CST Sun Jan 18 2026
.KEY MESSAGES...
- A cold front will bring a reinforcing shot of Arctic air
tonight. The combination of northwest winds and cold
temperatures will produce wind chills between -10 and
-15 degrees from late tonight through Monday morning.
- Dry and milder weather is expected Tuesday through Thursday.
- Another strong cold front arrives late in the week, along with
chances for precipitation into next weekend. Significant
discrepancies persist in long-range data, resulting in high
uncertainty regarding specific details.
&&
.SHORT TERM... (Through Late Monday Night)
Issued at 205 PM CST Sun Jan 18 2026
A weak northern stream system will move southeast from the Upper
Midwest through west-central and central Illinois this evening.
While mid-level saturation (750-500mb) and ascent are present, dry
air below 750mb will prevent much more than isolated flurries, if
that. Aside from flurries, thicker cloud cover will be the end
result from northeast Missouri through southwest Illinois. Even
drier air over central and southeast Missouri trend toward mostly
clear skies tonight.
A cold front trailing this system will bring a reinforcing shot of
cold air and increasing winds late this evening. The front`s
southward progression is expected to stall, keeping the core of the
coldest air to the north. Lows tonight will be similar to last
night. However, winds will be the difference with HREF
probabilistic guidance showing speeds exceeding 15 mph (>60%
probability) from Kirksville, MO, through Alton and Mt. Vernon,
IL. These factors will result in wind chills between -10 and -15
degrees. Recent HREF ensemble guidance shows 50-60% probabilities
for -10 wind chills now extend just south of I-70 in Illinois.
Therefore, I`ve added Madison, Bond, Fayette, and Marion Counties
to the cold weather advisory, which will go into effect at
3AM-10AM Monday morning.
High pressure moves southeastward, centered near the OK/AR border
Monday, with winds gradually subsiding and backing from the
northwest to the west-southwest to southwest in the pre-dawn hours
Tuesday. While warm air advection will begin to pull milder air in
from the southern Plains, it will not arrive in time to prevent
another cold night with lows in the upper single digits to low teens
early Tuesday morning.
Maples
&&
.LONG TERM... (Tuesday through Next Sunday)
Issued at 205 PM CST Sun Jan 18 2026
On Tuesday, the surface high will broaden and center over the
western Gulf as a shortwave trough moves into the central Plains.
This will enhance warm air advection, with west and southwest flow
drawing on milder mid-level temperatures. While air will be
seasonably milder (5C at the Front Range vs. -5C Locally), the
approaching trough drags another cold front through the region,
which stymies the northward advancement of warmer air, maintaining a
more westerly flow component. Temperatures return to near normal on
Tuesday, ranging from the low 30s to low 40s.
Wednesday is expected to be the warmest day of the week, with
temperatures rising into the upper 30s and mid-40s. Parts of
southeast Missouri and southwest Illinois may flirt with 50 degrees
as the warm mid-level air mass extends along and south of I-70. As
the shortwave tracks east into the Ohio Valley by Wednesday night,
it will reinforce colder air, dropping high temperatures by 5 to 10
degrees for Thursday.
The forecast becomes more complex late in the week as a stalled
front creates a sharp temperature gradient, ranging from the mid-20s
near the MO/IA border to the low 40s in southeast Missouri. Long-
range guidance remains inconsistent due to uncertainty regarding
boundary placement and the organization of impending disturbances.
Currently, deterministic ECM and GFS models show a cutoff
southwestern upper trough off the Baja Peninsula, while northern
stream disturbances continue to affect the northern U.S.
The late-week pattern is not conducive to deep, organized systems,
but it may eject multiple fragments of vorticity eastward from the
southwestern upper trough/low. These disturbances tend to track
along and over top the stalled boundaries. Key limiting factors
include the position of the Gulf high, which restricts moisture
return, and southward reinforcements of cold air with each
successive shortwave. The weak La Nia pattern suggests systems
often become better organized as they reach the eastern trough and
take advantage of strong baroclinicity. That being said, while a
stark, north-south temperature gradient exists in this timeframe,
there are no strong signals supportive of intensification, more
specifically over the mid-Mississippi Valley. One area of higher
confidence is in temperature trends. The strong cold front that
arrives late Friday brings a significant cooling trend toward the
end of the week into next weekend. Despite wide IQR spreads as much
as 15 degrees, IQR plots show a distinctive drop in temperatures
through next weekend with highs in the 20s and lows in the single
digits.
Maples
&&
.AVIATION... (For the 00z TAFs through 00z Monday Evening)
Issued at 530 PM CST Sun Jan 18 2026
Th primary concern during the 00Z TAF period is wind, as a
reinforcing cold front will push through the area this
evening/overnight and bring a round of gusty northwest wind. Wind
speeds are expected to be strongest prior to sunrise, but will
remain breezy through much of the day tomorrow. Wind speeds are
expected to diminish considerably by late afternoon tomorrow.
Otherwise, some patches of VFR stratocumulus will move through
terminals this evening and overnight, but flight category
reductions are not anticipated.
BRC
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Cold Weather Advisory from 3 AM to 10 AM CST Monday for Knox MO-
Lewis MO-Marion MO.
IL...Cold Weather Advisory from 3 AM to 10 AM CST Monday for Adams IL-
Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
Jersey IL-Macoupin IL-Madison IL-Marion IL-Montgomery IL-
Pike IL.
&&
$$
WFO LSX
NWS LSX Office Area Forecast Discussion
