Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 271121

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
521 AM CST Fri Jan 27 2023

.SHORT TERM... (Through Saturday Night)
Issued at 313 AM CST Fri Jan 27 2023

Surface analysis at 0800 UTC shows an area of low pressure near the
US-Canadian border, with a cold front draped to its south across the
Upper Mississippi Valley. The far southern end of this front is
forecast to move through the northern CWA late this morning into
early afternoon. This front is likely to pass through dry, though a
few snow showers are possible this morning in portions of northeast
Missouri and west-central Illinois. No accumulation is expected.

Temperatures ahead of this front will warm quickly, aided by partial
sunshine and strong low-level warm air advection. Winds at the
surface are also expected to veer more to the southwest, which
should promote some additional warming downslope off of the Ozark
Plateau. Low 50s are forecast in these locations in parts of central
and east-central Missouri. Elsewhere, some residual snow cover will
help limit the temperature rise a bit, keeping highs mostly in the
mid to upper 40s.

A subtle midlevel shortwave trough is forecast to move to our north
on Saturday, with a weak surface low passing through the northern
CWA. Widespread light to moderate snow is forecast north of this
feature across much of Iowa and northern Illinois. Further south,
chances of rain showers increase with the trailing cold frontal
passage Saturday night. As the low-level cold air comes in behind
the front, the rain may mix in with or briefly changeover to snow or
freezing rain/drizzle before ending. The reason that freezing
drizzle/rain is possible is that some model guidance suggests a
largely unsaturated dendritic growth zone. However, a trailing
shortwave trough may provide just enough midlevel ascent to
introduce ice crystals so went with a mix of freezing drizzle/rain
and snow later on Saturday night.


.LONG TERM... (Sunday through Thursday)
Issued at 313 AM CST Fri Jan 27 2023

(Sunday - Monday)

Canadian high pressure settles into the mid-Missouri Valley on
Sunday, bringing the mid-Mississippi Valley a period of cold and dry
weather conditions. High temperatures are forecast to return back a
bit below normal, with mid 20s in the northern CWA to low 40s in
southeast Missouri and southwest Illinois. Temperatures on Monday
will be a bit colder, generally topping out in the 20s to low 30s.
Those readings would be about 5-10 degrees below normal for the date.

(Monday Night - Tuesday Night)

This remains the main period of interest in terms of the potential
for wintry precipitation. Model trends over the past 12-24 hours
however show a stronger/further south placement of the surface high
pressure center. Consequently, higher odds for wintry precipitation
during this time frame have also shifted more toward the mid south.
That being said, there remains a lot of spread in ensemble data.
Many EPS members (~75%) still bring accumulating wintry
precipitation into the southern half of the CWA, with about half its
members showing at least 0.10" of liquid equivalent. The GEFS/CMCE
though show a much weaker signal for >0.10" of liquid equivalent,
with only about a 1 in 4 chance. At this time, maintained chance
PoPs for this period with the focus in the southern part of the CWA.
If it precipitates, snow or sleet are more favored at this time but
if the warmer (aloft) and wetter scenario like some of the EPS
members have verifies, then freezing rain would become an increasing

(Wednesday - Thursday)

Uncertainty increases further mid/late next week as guidance
struggles with how to handle the trough ejecting out of the desert
southwest. Most ensemble members of the CMCE/EPS/GEFS eject the low
during this time frame. Strong mid/upper level confluence across the
mid and Upper Mississippi Valley suggest this feature will either
stay south of the area, or weaken if it heads further north.
Therefore, dry weather is favored at this time along with continued
below normal temperatures.



.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 508 AM CST Fri Jan 27 2023

Gusty southwest winds are forecast today ahead of a weak cold
front. This front is expected to stall out across northeast
Missouri and west-central Illinois tonight. A few sprinkles or
flurries are possible near the front this morning around KUIN.
Otherwise, dry/VFR conditions are forecast through the period with
plenty of mid/high level cloudiness.





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