801
FXUS63 KLSX 300854
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
354 AM CDT Mon Sep 30 2024

.KEY MESSAGES...

- Isolated showers are possible again this afternoon across parts
  of south central and southwest Illinois into southeast Missouri.

- A cold front will move through the Mid-Mississippi Valley
  tonight into Tuesday morning bringing near to slightly below
  normal temperatures in the 70s to the area through Wednesday.

- The cooldown will be short-lived as temperatures warm back up
  into the 80s for Thursday and Friday.


&&

.SHORT TERM... (Through Wednesday)
Issued at 349 AM CDT Mon Sep 30 2024

The mid-upper level low that merged with the remnants of TC Helene
has sheared out into an open wave that`s stretched out from the
lower Tennessee Valley northeast into the Mid Atlantic states.  The
low level reflection of the wave is barely discernible in the
surface pressure field.  However the pressure gradient between it
and a high pressure system over eastern Canada continues to produce
easterly flow which is funneling low level moisture from the Ohio
Valley back into the Mid-Mississippi Valley.  This means we`ll have
to deal with one more day of scattered to broken clouds, mainly
across eastern Missouri and Illinois.  Deterministic guidance also
spits out very light QPF over south central and southwest Missouri
into southeast Illinois this afternoon, and the CAMs also develop
spotty convection in these areas.  Since we`re dealing with
basically the same setup as yesterday, and isolated showers
developed as expected yesterday afternoon, we`ll continue with the
20 percent chance for showers that`s in the going forecast for this
afternoon.  With that said, there should be fewer clouds, and the
the low level thermal ridge will be pushed east from the Plains into
Missouri and Illinois ahead of the next upstream short wave.  These
two factors will combine to bring warmer temperatures in the low to
mid 80s across most of the area.

A cold front associated with the aforementioned upstream short wave
is currently moving through the western Dakotas.  The short wave
will move quickly along the U.S./Canada border today into Tuesday,
and this will push the cold front southeast through the northern
Plains and Upper Midwest into the Mid-Mississippi Valley by early
Tuesday morning.  Guidance is in good agreement in timing the FROPA
through our area, entering northeast Missouri around 08-09Z, and
continuing southeast through central and east central Missouri by
12Z, and into far southeast Missouri by 18Z.  All guidance continues
to show this will be a dry FROPA for our area due to a lack of deep
moisture, but the wind will pick up from the northwest and likely
gust to 25-35 mph.  The northwest flow will bring a brief cool down
for Tuesday and Wednesday with highs mainly in the low to mid 70s
and lows in the 40s Wednesday morning.

Carney

&&

.LONG TERM... (Thursday through Sunday)
Issued at 349 AM CDT Mon Sep 30 2024

The short wave which will bring us the cooler weather Tuesday and
Wednesday attenuates the long wave pattern aloft, and the resulting
mid-upper level zonal flow will move the low level pattern along to
the east.  This will mean the cool high pressure that settles into
the Mid-Mississippi Valley will move over the Mid-Atlantic region
Thursday which turns the flow back to the south across the Mid-
Mississippi Valley resulting in a warm up back into the 80s.  Medium
range deterministic guidance begins diverging at the very end of the
week with the GFS bringing another cold front through Missouri and
Illinois on Friday driven by a deeper Mid-Upper level trough that
digs deeper into the eastern U.S.  The ECMWF is not as strong/deep
with the wave resulting in a weaker cold front and warmer airmass
over Missouri and Illinois for the weekend.  LREF is picking up on
these differences, showing a temperature spread of up to 10 degrees
between the 25th and 75th percentile.  While the NBM is showing a
bit of a cool down for the weekend, this continues to be a low
confidence forecast at this time.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1050 PM CDT Sun Sep 29 2024

Clear skies over central Missouri through northeast Missouri in
combination with light winds will favor the development of fog at
KJEF and KCOU overnight. Expect fog to cause MVFR visibilities with
a potential for periods of IFR visibilities at KJEF. Fog is also
possible at KSUS. Fog will dissipate shortly after sunrise.

Cloud cover over eastern Missouri and southern illinois will persist
through the overnight hours and ceilings are expected to lower to
MVFR status at KSTL, KSUS, and KCPS early Monday morning. Ceilings
should lift to VFR by mid-morning. Otherwise, surface high pressure
over the region will winds light through the TAF period.

MMG/Glass

&&

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

$$

WFO LSX