331
FXUS63 KLSX 121623
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
Issued by National Weather Service Lincoln IL
1023 AM CST Wed Feb 12 2025

.UPDATE...
Issued at 1015 AM CST Wed Feb 12 2025

Radar reflectivity shows precipitation moving west to east through
eastern sections of Missouri with pockets of higher reflexivity
(bright banding) along and southe of I-44 indicating partial
melting aloft with relatively higher precipitation rates.

Reflectivity drops off over central Missouri, westward through
Kansas City. Short term guidance shows drier air gradually working
into the back side of the system after the noon hour, while HREF
ensembles indicate the DGZ becoming unsaturated as far east as
the St. Louis Metro Area between 1PM-3PM. This gives some pause as
to whether snowfall amounts will materialize in broader coverage as
previously expected. What leaves me of the fence with exactly how
the rest of the event will play out is a narrow SW/NE oriented
band of enhanced mid-level frontogenesis that could result in some
redevelopment before moisture is lost.

All-in-all, this continues to follow the quicker, lower QPF
trends over the last 24 hours. We will continue to monitor an area
over northeast Oklahoma, where scattered pockets of higher
reflectivity are likely to track east over southern sections of
Missouri, albeit in an area that is expected to warm slightly
above freezing through the afternoon. The current thinking is that
the wave of more persistent snow/sleet will occur this morning
into early afternoon with a transition to lighter precipitation or
drizzle late this afternoon/evening. Despite the lower amounts
(especially to the north of I-70), temperatures will be key in how
impacts linger considering that most areas north of I-44/I-70
will remain near/below freezing through the day.

Maples

&&

.KEY MESSAGES...

- Main changes with this forecast package for today`s winter storm
  were to reduce snowfall totals in/near the warning area and to
  shift the snow/sleet transition zones to the southeast.

- A Winter Storm Warning remains in effect for portions of
  central and northeast Missouri as well as west-central Illinois
  today. Snow totals of 2-5" are forecast in these areas. Further
  south, a Winter Weather Advisory is in effect for snow
  (including some sleet) and ice accumulations.

- Travel impacts are likely today, especially to the afternoon
  rush hour.

- Near/below normal temperatures are expected to extend through
  the long term period. Another system will bring rain to the
  region Friday night into Saturday with a possible transition to
  snow before ending Saturday afternoon/night.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 320 AM CST Wed Feb 12 2025

The winter storm which will impact the area today has continued to
trend weaker, quicker over the past 24 hours. These trends mean
less total QPF, and therefore, lesser snowfall totals in
central/northeast Missouri and west-central Illinois. Most of that
region is likely to see 2-4" of total snow, though a few isolated
locations may see 5". Therefore, left the warning continue though
it appears very unlikely many locations will actually see 5"
(warning criteria). The weaker trends farther to the south also
have impacts, namely on precipitation type. More snow and sleet is
forecast now well into east central Missouri and south-central
Illinois. The precipitation will be mostly light, other than
potentially some more moderate rates within a 2-3 hour window.
Total snow/sleet amounts in the advisory area will range from 1-2"
for most. Not much has changed however with respect to freezing
rain amounts. Freezing rain accretion will not be efficient at all
given air temperatures near freezing and this occurring near
solar noon. Roadways likely will be okay, other than perhaps some
bridges and overpasses. Elevated surfaces including trees however
will be more able to accrete some ice (glazing to as much as
0.10").

The other change made to today`s forecast was to quicken the exit
of the precipitation from west to east by about an hour or two.
This was made as these warm air advection events are typically
quicker to begin and end, and now also closely matches rapid-
update guidance (HRRR/RAP).

Behind this system, winds will turn out of the northwest, tapping
into the nearby reservoir of arctic air currently sitting across
the mid-Missouri Valley and Upper Midwest. Lows in the mid single
digits (above zero) to mid teens are forecast from northwest to
southeast.

Very cold temperatures are forecast areawide tomorrow, with highs
generally in the 20s. These readings would be some 15-20 degrees
below normal for the date. The good news? We are expecting plenty
of sunshine at least.

Gosselin

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 320 AM CST Wed Feb 12 2025

(Thursday Night - Friday)

Thursday night still is on track to be very cold, though the
timing of the surface anticyclone has sped up about 3-6 hours
compared to yesterday. This means that there may be some weak
southerly return flow across parts of central and northeast
Missouri after roughly 0900 UTC Friday. Another factor that looks
like it has changed since yesterday is we are not expecting as
much snow cover in those areas. Both of these factors have led to
warmer low temperatures compared to yesterday. All that being
said, it still looks very cold, with lows in the upper single
digits to mid teens.

Increasing southerly winds around the western periphery of the
departing surface high should help warm temperatures up on Friday
into the mid 30s to low 40s.


(Friday Night - Tuesday)

A storm system is expected to bring widespread rain to the area
Friday night into Saturday as a lead midlevel shortwave ejects out
of the desert southwest. There remains uncertainty on to the
timing/track/strength of a secondary shortwave Saturday
afternoon/night. This wave may be able to interact with the low-
level baroclinic zone to produce some light snow back into the
colder air. Probabilities for at least 1" of snow ending Sunday
morning have dropped a bit on the latest LREF, but are still in
the 20-40% range.

Behind this system, another push of arctic air appears likely,
with GEFS/EPS 850-hPa temperature anomalies of -10 to -15C. Lows
in the single digits/teens and highs mostly in the 20s are
forecast Sunday through Tuesday. Below zero lows are even a
distinct possibility Monday morning across parts of northeast
Missouri and west-central Illinois. The LREF shows 30-50%
probabilities for below zero lows.

The next chance of precipitation (snow) comes Monday into Tuesday.
There is quite a bit of spread, but WPC 500-hPa clusters generally
show a weak midlevel shortwave trough moving through the southern
Plains/mid south. There are of course plenty of unknowns, but any
precipitation that does occur in the area through at least
early/mid next week would be all snow. At this very early
juncture, the LREF shows the best chances of light snow (0.10"
liquid equivalent) in the 20-40% range centered across southern
Missouri/Illinois. There are however a smaller minority (10-20%)
of members that have 0.30+" of precipitation. Given the arctic air
mass in place, ratios could be quite high so this is a system is
one to keep an eye on over the next several days.


Gosselin

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 530 AM CST Wed Feb 12 2025

Conditions will quickly deteriorate this morning. Light snow will
increase in intensity as it spreads east/northeast. Some mixing is
expected in the metro terminals, mainly some sleet with the snow.
IFR visibilities are expected for at least a few hours, with
minimum visibilities of 1/2 SM with moderate snow possible. The
precipitation will move out this afternoon, with ceilings lifting
above 1000 feet AGL this evening.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory until 6 PM CST this evening for Callaway
     MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO-
     Jefferson MO-Lincoln 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 Storm Warning until 6 PM CST this evening for Audrain MO-
     Boone MO-Knox MO-Lewis MO-Marion MO-Monroe MO-Pike MO-Ralls
     MO-Shelby MO.

IL...Winter Weather Advisory until 6 PM CST this evening for Bond IL-
     Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Randolph IL-Saint Clair IL-Washington IL.

     Winter Storm Warning until 6 PM CST this evening for Adams IL-
     Brown IL-Pike IL.

&&

$$

WFO LSX