618
FXUS63 KLSX 301749
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1149 AM CST Sun Nov 30 2025

.KEY MESSAGES...

- Confidence is high (90%+) in another round of snow Monday into Monday
  night. The greatest totals (up to 4") are forecast across
  northeastern Missouri and west-central Illinois.

- Multiple intrusions of Arctic air will keep temperatures
  running well below normal through the week.


&&

.SHORT TERM... (Through Monday Night)
Issued at 340 AM CST Sun Nov 30 2025

Morning surface observations show the low responsible for
yesterday`s snowfall is moving through the Great Lakes; its
attendant cold front clear of the CWA and moving through the Ohio
Valley. In the wake of this front, an Arctic air mass is advecting
into the region, with temperatures running about 5-10 degrees colder
than at this point yesterday morning. As this air mass moves further
into the region, temperatures will struggle to warm much today, with
mid-20s and low-30s expected for highs. This will set the stage for
lows tonight dropping into the teens for most locations.

Our attention turns toward another winter system set to impact the
region Monday into Monday night. An upper-level trough currently
seen in water vapor imagery over the Pacific Northwest will eject
out into the Plains on Monday and its surface reflection will
develop along the Gulf Coast and move through the Southeast. North
of the low across the Middle Mississippi Valley, frontogenetical
forcing will produce a band of mostly light to moderate snowfall
that will move east-southeastward through the day and into the
night.

While the lower levels of the atmosphere will initially be quite dry
as this forcing enters the region, increasing southwesterly flow
will help saturate the lower to mid-levels, including within the
dendritic growth zone (DGZ), leading to snowfall. As the
frontogenetical band moves through the CWA, deterministic soundings
show lift occasionally maximized within the DGZ, with some
potential for an isothermal layer within the DGZ. These factors
point to snow-to-liquid ratios at or just above climatology. With
the guidance consensus on QPF being around 0.15", confidence is high
in a dusting to an inch of snowfall for the entire CWA (up to 90%
chance per the NBM). A majority of deterministic models show a
narrow corridor of 0.2-0.3" of QPF occurring north of I-70,
somewhere around the Highway 36/I-72 corridor. With SLR forecast to
be 14:1-16:1, this amount of QPF would yield a band of up to 4" of
snowfall, maybe as much as 5". Given the spread of solutions and the
narrow corridor over which it would fall, blended guidance such as
the NBM is likely not accurately depicting it, with the probability
of such a threshold only topping out around 40% within the NBM.

Snowfall rates within this band will be around 1"/hr at times,
leading to rapid deterioration of travel conditions. Further south
across the CWA where amounts will be relatively lighter, at least
minor impacts to travel are still expected, especially if
snowfall occurs during the evening rush hour such as in the St.
Louis metro. Through Monday evening into the overnight hours, the
focus for snowfall will shift east-southeastward, eventually
departing the CWA during the early morning hours. Warm air
advection will produce a warm nose that has a low chance of
causing sleet to mix in at times with the snow across far
southeastern Missouri.

Timing and placement of the greater amounts of snowfall are expected
to come into better view within the next 12-18 hours, which will
allow for headline decisions.

Elmore

&&

.LONG TERM... (Tuesday through Saturday)
Issued at 340 AM CST Sun Nov 30 2025

Tuesday morning, both deterministic models and ensemble clusters
show that the axis of the upper-level trough responsible for
Monday`s snow will either be directly over the CWA or just to the
east. This supports snowfall ending by Tuesday morning at the
latest. As the upper-level flow deamplifies and becomes zonal aloft
through the day and into Wednesday, a surface ridge will nose into
the region with low-level flow becoming increasingly south-
southwesterly. Temperatures will respond by warming notably on
Wednesday, with ensemble means supporting afternoon highs at least
in the mid to upper 30s. Locations south of I-70 have the best
chance for reaching and exceeding 40 degrees, where the NBM has the
probability of such threshold being around 60%.

This relative warm up will be short lived, with guidance consensus
having a cold front delivering another Arctic blast Wednesday night
through Thursday night. Spread within the IQR of global ensembles is
still quite high (around 10 degrees), leading to low confidence in
specific temperatures through this portion of the period. However,
it will indeed be cold, as the 75th percentile from the NBM has a
majority of the CWA failing to reach freezing, with 20s north of I-
70 for highs on Thursday. The 75th percentile also has lows
Wednesday and Thursday nights in the teens for areas south of I-70
and low teens to single digits north of I-70.

As a shortwave digs into the Plains and heads toward the Middle
Mississippi Valley on Friday, low-level flow will quickly become
south-southwesterly, giving temperatures a boost. The shortwave
along with an upper-level jet streak will lead to a threat of
precipitation (40% chance), with ensembles trending increasingly
toward this solution over the last couple initializations. Warm air
advection precipitation over a retreating Arctic air mass supports
the threat of frozen precipitation, though uncertainty with the
degree of warm air advection aloft leads to low confidence in
precipitation type at this lead time.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1139 AM CST Sun Nov 30 2025

A broad area of MVFR stratus/stratocumulus with bases from
1500-2500 AGL is drifting southward this afternoon. The clouds
should continue moving south for the rest of the afternoon into
the evening, and overspread the entire forecast area by 05-07Z.
Bases are expected to rise to VFR range after 12Z Monday morning
in all areas except northeast Missouri and west central Illinois.
There ceilings may fall to IFR range by 12-15Z.

Carney

&&

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

$$

WFO LSX