574
FXUS63 KLSX 191041
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
441 AM CST Sun Jan 19 2025

.KEY MESSAGES...

- The very cold conditions will continue through early Wednesday with
  coldest wind chills expected to drop to around -10 degrees
  early on Monday morning and Tuesday morning over parts of the
  area. A Cold Weather Advisory is in effect for tonight and
  Monday morning for parts of south central Illinois.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 346 AM CST Sun Jan 19 2025

Northwest winds continue to bring a steady stream of cold air early
this morning and will continue to do so throughout the day today.
This cold air advection along with the clouds which will linger into
the afternoon will cause temperatures to only have about a 5 degree
diurnal rise today.  The HREF is showing a surface high dropping
through the Plains into southern Missouri tonight which will keep
winds out of the west over the CWA into early tomorrow morning.
Latest temperatures guidance supports lows tonight falling into 0 to
+6 degree range with the "warmest" temperatures in the St. Louis
metro. Wind chills will fall below zero across the entire area, with
minimum readings late tonight and early Monday around -10F over the
northern and eastern parts of the CWA. Have issued a Cold Weather
Advisory late tonight into Monday morning where these readings meet
criteria over south central Illinois.  Highs on Monday will be a few
degrees higher as we go into neutral temperature advection and there
will be more sun.

Regional radars are showing light returns over the far southern part
of the CWA early this morning which may be producing some light
flurries.  This light precipitation has developed ahead of a mid-
level trough currently entering western Missouri that will move east
of the area later this morning.  Then dry weather is expected today
into tomorrow as subsidence develops in the wake of the trough.

Britt

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 346 AM CST Sun Jan 19 2025

Another very cold night is expected on Monday night as the NAM/GFS
is showing another surface high moving into western Missouri late in
the night causing skies to clear and winds to decrease.  Forecast
lows in the single digits including near 0F over central and
northeast Missouri and west central Illinois look reasonable given
that the airmass is expected to be the coldest (i.e. 850mb
temperatures around -25C). Here again, most of the area will see
wind chills below zero with wind chills around -10F over the
northern CWA.  The LREF probabilities are depicting a 50-70% chance
of AOB -10F apparent temperatures as far south I-70 on Tuesday
morning, so will need to monitor the need for an additional advisory
if there is a slight change in the wind or temperature forecast.

There is good agreement in the model guidance that a deep upper
trough that is responsible for the cold will lift out of the central
CONUS by late Tuesday with a second trough dropping into the Midwest
behind it on Thursday.   This second trough will not have the deep
cold with it, and the models have been consistent the past few day
with a moderating trend with highs Wednesday through Friday in the
30s. Forecast highs by next Saturday are in the 40s across the CWA
in southwesterly low level flow with the NBM IQR only being 5
degrees.

Will keep the forecast dry as >90% of the NBM and LREF members are
dry through Saturday.  Still could not totally rule out a low chance
or rain or snow late in the week as the deterministic models are
still depicting some spotty, light QPF with the passage of the
second upper trough.  A better chance for precipitation may wait
until after the forecast period late next weekend.

Britt

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 439 AM CST Sun Jan 19 2025

Dry and VFR conditions are expected through the period. Northwest
winds will gust into the 20-25 knot range early in the period, but
will gradually decrease to around 10 knots after 00Z.

Britt

&&

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

$$

WFO LSX