544
FXUS63 KLSX 222302
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
502 PM CST Wed Jan 22 2025

.KEY MESSAGES...

- There is still a low chance of light snow (30-50 percent) across
  parts of northeast Missouri and west-central Illinois through
  this evening with perhaps a dusting possible. Elsewhere there is
  a chance of flurries later tonight into Thursday morning across
  parts of the area.

- Colder temperatures return on Thursday, with a moderation
  expected to begin on Friday.

- A return to above normal temperatures and highs in the 40s
  remains on track for Saturday.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 234 PM CST Wed Jan 22 2025

Except for the West Coast, the CONUS remained under the influence of
a large deep long wave trof centered through the middle of the
Nation. Pre-frontal southwest low-level flow is currently bringing
warmer temperatures to the region and has displaced the last of the
Arctic Air well to the east. A short-wave trof moving through the
longwave will move through the region tonight driving a cold
front through the area. There is currently a region of weak large
scale ascent centered over the CWA and where it overlaps on the
northwest fringe with weak low-mid level frontogenetical forcing
we are see some weak returns on radar across northwest MO. Nothing
appears to be reaching the ground, likely owing to both the weak
overall forcing as well as notable dry sub-cloud layer air. This
area of juxtaposed forcing will translate eastward through the
remainder of the afternoon and into the evening ahead of the
advancing cold front, largely centered from the NE MO/WC IL
northward. Dry air will remain a negative issue although there
may be a brief window where the low-levels moisten enough for
light snowfall. In general most of the guidance has rather low
probabilities of snow, let alone measurable snow. The HREF
ensemble max snowfall has little to none, so probably a worst case
scenario is the potential for a few spots in NE MO and WC IL
seeing a dusting.

In the wake of the cold front tonight, and lasting into Thursday
morning across the southern CWA, will be a slug of lower-clouds and
we could see a few flurries accompanying it within the CAA regime.
After the nice temperature moderation today, a Polar Air Mass will
dominate the area Thursday and Thursday night. A return to colder
temperatures will accompany it with temperatures around 10-15
degrees below normal. Highs on Thursday should be in the
20s-lower 30s and lows Thursday night mainly in the single digits
as the surface ridge axis moves into the area.

Glass

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 234 PM CST Wed Jan 22 2025

A pattern change will commence Friday into early next week and
this will lead to largely warmer temperatures. The last short-wave
trof translating within the longwave will exit the region on
Friday morning. Large height rises aloft are expected in its wake
Friday-Saturday as flow returns to more quasi-zonal along with an
attendant low-level WAA regime. Temperatures should be warmer on
Friday and this could possibly be a day where they overachieve
from our current forecast. Our forecast for Saturday is just above
the 50th percentile on the NBM and highs look solidly at least in
the 40s, however we might see some lower 50s from the MO River
southward if the 90-95th percentile temperatures are more
accurate.

The pattern change that will take place into the weekend will
initially feature a split flow regime with a closed low/trof
centered over southern CA and new upper trof over eastern NOAM. A
cold front will move through the area on Saturday night
accompanying this evolution and the dominance of eastern upper
trof and northwest flow across our area, and this has also
resulted in precipitation chances Sunday Night continuing to get
shunted southward out of the area. At this point the threat of
measurable precipitation is 15-20% and confined to far SE MO and
southern IL. Despite some differences in the depth of the eastern
NOAM trof and the progression of the southwest upper low heading
into midweek, the general trend has favored a return to above
normal temperatures Monday-Wednesday and the entire lower quartile
of the NBM temperature guidance is above normal.

Glass

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 454 PM CST Wed Jan 22 2025

Surface winds across the area will turn from
southerly/southwesterly to northwesterly behind a cold frontal
passage tonight. Post frontal wind gusts of up to 20-25 kts are
expected. Light snow is forecast ahead of the front with northeast
MO and west-central IL having the greatest chance at seeing a
dusting. MVFR ceilings will follow the frontal passage, covering
most of the forecast area into Thursday afternoon.

Jaja

&&

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

$$

WFO LSX