Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

557
FXUS63 KLSX 141107
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
507 AM CST Sun Dec 14 2025

.KEY MESSAGES...

- Expect dangerous wind chill readings between -10 and -20 this
  morning across much of eastern Missouri and Illinois.

- Temperatures will warm up rapidly to near normal on Monday, and
  then well above normal for Tuesday through Thursday.

- The next significant chance for precipitation will be late
  Wednesday night and Thursday. No wintry precipitation is
  expected with this system.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 256 AM CST Sun Dec 14 2025

A sprawling Arctic high pressure system will move from the East
Central Plains into the Mid Mississippi Valley today.  Temperatures
are bottoming out between 0 and 6 above zero across most of the
area, but parts of northeast Missouri into central Illinois are
hitting to 4 degrees below zero. These temperatures combined with
10-12kt winds are producing dangerous wind chill readings of -10 to
-20 degrees across northeast and east central Missouri into central
Illinois this morning.  The Cold Weather Advisory therefore looks
like it`s in good shape, and I do not anticipate any changes to it
at this time.  Continuing cold advection on northwest flow as the
high builds into Central Illinois will suppress the diurnal warm up
today, and highs will struggle to reach the mid to upper teens in
most locations.  Farther north where new snow fell yesterday, highs
may not top 10 degrees this afternoon.  Temperatures fall a few
degrees this evening, particularly across the snow field in
Illinois.  However the center of the high will move east of the area
into the Ohio/Tennessee Valley by 03Z which will turn the wind to
the south-southwest which will cause temperatures to become steady
by late evening and then rise slowly after midnight.

Carney

&&

.LONG TERM...  (Monday through Saturday)
Issued at 256 AM CST Sun Dec 14 2025

The Arctic high will continue moving southeast Monday, finally
settling into the southeastern U.S. late Monday night/Tuesday. THis
will keep the Mid Mississippi Valley in persistent south-southwest
flow facilitating a rapid warm up to near normal temperatures on
Monday, and then above normal for Tuesday through at least Thursday.
A weak short wave trough zips through the Midwest late Tuesday
night/Wednesday and tries to push a cold front through Iowa into
Missouri.  However, a short wave ridge right behind the trough
builds in quickly, keeping the cold air bottled up in the Upper
Midwest.  With that in mind, there is some uncertainty on how far
south the front will make it into Missouri and central Illinois.
Ensemble high temperature IQRs increase from only 2 degrees Tuesday
to 5 to 7 degrees on Wednesday.  Regardless, even the 25th
percentile is still well above normal in the mid 40s to low 50s.

Guidance shows another, much deeper trough moving through the
Mississippi Valley on Thursday.  Both the deterministic GFS and
ECMWF show the system tapping into some Gulf moisture and they also
produce a bit of instability ahead of the front between 06-12Z
Wednesday.  The ECMWF even shows 850mb LI values falling below zero
in that time frame.  NBM added in some ~20% thunder between 06-12Z,
and this looks reasonable given the GFS` and ECMWF`s forecast.  Both
models show the primary cold front sweeping through the forecast
area between 12-18Z, and then a secondary front with much colder air
drops in during the late afternoon/early evening.  All of the precip
associated with this system still looks like it will be liquid as
the cold air arrives too late to interact with the moisture.  A
colder high pressure builds into the Mississippi Valley Friday,
bringing temperatures back to near normal in the upper 30s to mid
40s, but the high moves quickly eastward bringing southerly flow and
above normal temperatures back to the region on Saturday.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 505 AM CST Sun Dec 14 2025

VFR flight conditions are expected to prevail through the period.
Northwest wind will become light and variable this afternoon as
the center of a strong high pressure system moves across the area.
Winds will then turn to the southeast this evening and continue to
veer to the south overnight as the high moves into the Ohio and
Tennessee Valleys.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Cold Weather Advisory until noon CST today for Knox MO-Lewis MO-
     Lincoln MO-Marion MO-Pike MO-Ralls MO-Saint Charles MO-
     Saint Louis City MO-Saint Louis MO-Shelby MO.

IL...Cold Weather Advisory until noon CST today for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX