786
FXUS63 KLSX 231637
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1037 AM CST Sun Feb 23 2025

.KEY MESSAGES...

- Mild temperatures are expected through the week.

- The forecast remains dry except for Wednesday when there will be
  a 20-40% chance of rain.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 304 AM CST Sun Feb 23 2025

High pressure centered over the central Appalachians this morning
will drift a bit eastward today.  The pressure gradient between this
high and a trough of low pressure over the northern and central
Plains will continue to produce southwest flow across the Mid
Mississippi Valley today.  This will continue our warming trend from
last week`s record setting cold snap.  Should see plenty of sunshine
today in addition to warm southwest flow.  NBM tends to be a little
laggy with temperatures in these situations, so I leaned on the 75th
percentile for temperatures today which bumps highs up into the low
to mid 50s in most locations.  It looks cooler in the upper 40s in
south central Illinois which will be closer to the retreating cold
air mass.

Winds drop off again during the evening and a mostly clear sky will
allow good radiational cooling.  Temperatures should drop quickly
back into the 30s and low 40s.  However the trough over the Plains
will be moving into the Mississippi Valley overnight, and the
increasing pressure gradient between it and the surface ridge still
hanging over the Appalachians will produce increasing southwest flow
overnight.  After the initial drop in the evening, temperatures
should steady out or rise a few degrees through sunrise Monday.
Clouds will also increase ahead of the trough overnight which will
also limit any further cooling.

Warm advection in southwest flow continues for most of Monday ahead
of the trough.  With the warmer start to the day, high temperatures
should be several degrees warmer than Sunday.  Once again leaned
toward the NBM 75th percentile which yields highs in the mid 50s to
low 60s.

Carney

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 304 AM CST Sun Feb 23 2025

The short wave driving the surface trough through the Mississippi
Valley on Monday is forecast to mainly stay over Canada, the Upper
Midwest and Great Lakes region, and the surface low stays well north
of the U.S./Canada border near Hudson Bay. With this pattern,
there`s little or no cold advection behind the trough Monday
night/Tuesday.  Tuesday morning lows/afternoon highs look very close
to Monday`s, if not a couple degrees warmer as the air mass
continues to modify.

The first and (so far) only chance for rain in the forecast is still
on Wednesday.  The LREF cluster analysis reveals the models are
still having trouble resolving the amplitude and timing of the short
wave as it moves across the Mississippi Valley on Wednesday, so
temperatures and the timing of the precip remain uncertain at this
time.  The deterministic ECMWF and GFS are actually in pretty good
agreement on Wednesday, pushing the cold front and light QPF
associated with this system through the forecast area during the
daylight hours. The deterministic GFS even develops ~200 J/Kg MUCAPE
across the eastern Ozarks and southwest Illinois Wednesday
afternoon. However only about 30% of the LREF members show any
MUCAPE at all, and of those that do the majority are 100 J/Kg or
less.  At this point in the forecast I don`t think putting in a
mention of thunder is warranted, however it bears watching.

Mild temperatures continue ahead of the front Wednesday, but cooler
air spills in behind the front Wednesday night.  The air mass behind
the front still doesn`t look terribly cold, and temperatures are
only forecast to be a few degrees cooler on Thursday.  With that
said, it should be noticeably cooler.  The NBM knocks temperatures
back from the upper 50s to low 60s on Wednesday to the low to mid
50s on Thursday. Additionally, the LREF cluster analysis shows
increasing uncertainty in how amplified the short wave trough will
get over the Ohio Valley and East Coast Thursday. The deeper
solutions would yield stronger cold advection behind the front, and
therefore colder temperatures than currently forecast for Thursday
and Friday.  With that in mind, interquartile temperature ranges
show an increasing spread for the end of the week into the weekend,
especially on Saturday when a long wave trough is forecast to dig
into the Ohio Valley.  However, even the 25th percentile
temperatures for Thursday through Saturday remain near or above
normal for late February.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1033 AM CST Sun Feb 23 2025

Dry and VFR flight conditions will continue through the remainder
of the TAF period. Southwesterly winds will increase to around 10
kts today before going calm for the first half of the evening.
Winds will increase overnight as the surface pressure gradient
tightens and will remain elevated (around 10 kts) tomorrow. A few
gusts are possible across KCOU, KJEF, and KUIN, but confidence is
highest at KUIN.

Delia

&&

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

$$

WFO LSX