Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

581
FXUS63 KLSX 280503
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1103 PM CST Sat Dec 27 2025

.KEY MESSAGES...

- A strong cold front will move through the area tomorrow bringing
  a marginal risk for severe thunderstorms with threats of locally
  damaging winds or a brief tornado.

- Gusty winds of 35-45 mph behind the front will usher in an
  Arctic airmass Sunday night into Monday. Wind chill values will
  dip near, or even just below 0 on Monday morning.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 1232 PM CST Sat Dec 27 2025

An active short term period is expected as a potent mid/upper
level trough brings a drastic change in season for us Sunday
night into Monday. As of this afternoon, the fog that has plagued
us for days is finally starting to lift and erode away from the
southwest as a surface warm front lifts northeast in response to
the incoming trough. Expect this fog to continue to lift/erode
through the late afternoon hours, and even into the evening as
the front continues it push to the northeast.

It will be a mild night as southerly flow and clouds keep
temperatures in the 50s and 60s. A stout low-level jet of of 40-50
knots will pump anomalous Gulf moisture into the region late
tonight into Sunday morning. This will set the stage for
convective potential through the day on Sunday.

The first chance of thunderstorms will come as early as Sunday
morning. Mean MUCAPE values from the 12Z HREF suggest 500-1000
J/kg will be available on the nose of that low-level jet, which
will lead to elevated convection across northeast MO and western
IL. It`s possible some of this activity could have some small hail
in it, but suspect any hail should remain just below severe
limits Sunday morning.

The more appreciable severe threat will come Sunday afternoon as
the mid-level trough approaches, helping to sharpen a potent cold
front that will race through the region Sunday afternoon. The
latest guidance has continued to slowly tick upward with available
surface-based instability, with at least 250 J/kg of SBCAPE now
likely (50-60%) and 500 J/kg of SBCAPE about 20-30% likely. The
HRRR is the most aggressive with instability progs depicting
upwards of 750 J/kg of SBCAPE. The intensity of mid-level ascent coupled with
the strong frontal convergence should favor a pretty quick
transition to a linear more. While instability still remains a
limiting factor in the intensity of this event, I do think we will
have just deep enough linear convection to allow for some
isolated instances of damaging winds mainly from eastern MO into
western and southwestern IL. 0-3km shear will be strong, topping
out around 45-50 knots, which will be enough for mesovortex
creation as well, especially within any linear feature that can
surge and orient more northwest to southeast to take advantage of
the 0-3km shear vector orientation.

Immediately behind the front, gradient winds will ramp up as the
Arctic airmass spills into the region Sunday evening into Sunday
night. Would not be surprised to see some gusts approach 45 mph
(Advy criteria) Sunday night into Monday, but did not quite have
the confidence to go with a Wind Advisory quite yet. Otherwise,
temperatures will quickly plummet behind the front. Fortunately
with the gusty winds and not much precipitation expected along the
quick-moving front, I do not expect any flash freeze issues as
roadways should dry out before we dip below freezing behind the
front Sunday night.

Deitsch

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 1232 PM CST Sat Dec 27 2025

The start of the long term period Monday will feature temperatures
about 50(!) degrees colder than they were on Sunday afternoon. The
deep mid-level trough responsible for this Arctic airmass will have
pushed into the Great Lakes region leaving deep northwesterly flow
in its wake. Gusts of 35-45 mph will keep wind chill values in the
single digits and teens throughout the day on Monday, a stark
contrast to what we have seen the past several days!

Fortunately, the Arctic airmass will be short lived as heights will
already begin a slow rise by Tuesday. Surface winds should switch to
the west by Tuesday afternoon which should allow for at least some
temperature moderation, with highs expected in the low to mid 30s
(about 10 degrees warmer than Monday). Wednesday will be warmer yet,
with highs in the 40s across most areas.

Confidence in the overall pattern decreases by Thursday and beyond.
The main source of uncertainty is with how deep the next trough
embedded within the northwest flow will become and consequently what
access it will have to another additional blast of Arctic air.
Reviewing cluster analyses, it appears the bulk of the ensemble
members are on the deeper trough/colder solution, which is well in
line with the deterministic NBM. Therefore, highs in the upper
20s/low 30s seem reasonable for now, but it`s worth noting that the
interquartile temperature spread Thursday through Saturday are
nearly 20 degrees! Fortunately, it continues to look mostly dry
through the period despite the continued uncertainty in
temperatures.

Deitsch

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1102 PM CST Sat Dec 27 2025

A warm front has passed all terminals but KUIN, where IFR clouds and
fog will likely persist until sometime Sunday morning. Showers and a
few thunderstorms are expected to increase in coverage north of I-70
Sunday morning as well, potentially impacting KUIN. Elsewhere, MVFR
ceilings expand in coverage after sunrise, remaining overhead
through most of Sunday. A cold front will also pass through the area
midday Sunday into the afternoon, but confidence is decreasing that
it will be accompanied by showers and thunderstorms. The front will
at least veer winds from southerly to northwesterly with gusts
increase to 30 to 37 kt. These winds will continue through Sunday
night, but eventual lifting/scattering of MVFR ceilings is favored
sometime around or just beyond the valid TAF periods.

Pfahler

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 6 AM CST Sunday for Knox MO-Lewis MO-
     Marion MO-Monroe MO-Ralls MO-Shelby MO.

IL...Dense Fog Advisory until 6 AM CST Sunday for Adams IL.

&&

$$

WFO LSX