Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

235
FXUS63 KLSX 131116
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
616 AM CDT Fri Mar 13 2026

.KEY MESSAGES...

- There is a threat of strong to severe thunderstorms Sunday
  afternoon and evening, mainly across portions of southeastern
  Missouri. The primary threat is damaging wind gusts, with the
  lesser threat being tornadoes.

- There is a 50-60% chance of 2" of snowfall accumulation north
  of I- 70 in Missouri and across west-central Illinois Sunday
  night into Monday morning.

- Anomalously cold temperatures are expected Monday morning
  through Tuesday.


&&

.SHORT TERM... (Through Saturday Night)
Issued at 324 AM CDT Fri Mar 13 2026

Early morning water vapor imagery shows expansive upper-level
troughing over nearly the entire CONUS, with northwesterly flow
stretching from the Pacific Northwest toward the East Coast. Within
this flow, a tightly-wound shortwave is moving into the Great Lakes
region; its surface reflection visible in observations spinning
across central Minnesota. A tight pressure gradient thanks to the
surface low and a strong low-level jet (60-70 knots per SPC
Mesoanalysis and ACARS soundings) sinking eastward into the Lower
Missouri Valley will continue to yield gusty winds through mid
morning. Where confidence is greatest in wind gusts reaching and
exceeding 45 mph through this time range, a Wind Advisory remains in
effect. This continues to be areas generally north of I-70, where
the 00z HREF has a 90% chance of gusts of this magnitude.

An attendant cold front will swing through the CWA by mid to late
morning, signaling a decrease in wind speeds as they shift to out
of the northwest. The winds through the depth of the atmosphere will
be west-northwesterly, leading to weak cold air advection at best
with an airmass that originates from the Pacific. As a result,
temperatures this afternoon will at least be comparable to what was
experienced Thursday, with even warmer temperatures south of I-70
thanks to less cloud cover and warmer temperatures at 850 mb.
Temperatures will warm further on Saturday as subtle ridging builds
into the Midwest, causing low-level winds to become southerly and
advect warm air into the CWA. The 01z NBM and our current forecast
calls for Saturday`s highs reaching the 60s to low 70s for most
locations; though this is on the warmer side of guidance, and a more
southeasterly component to the surface winds prevents confidence
from being high in specific values. However, this warmer solution is
within reasonable bounds and has not been modified.

Elmore

&&

.LONG TERM... (Sunday through Thursday)
Issued at 324 AM CDT Fri Mar 13 2026

Confidence is high in an amplified trough digging into the center of
the CONUS Sunday, sending a strong low pressure system through the
Midwest. Deep south-southwesterly flow ahead of this system will
pump warm, moist air into the region through the day Sunday, with
anomalously warm temperatures expected through the day beneath
increasingly cloud skies. This warmth will increase instability
across the region, pairing with ample deep-layer shear (around 50
kts) to lead to a threat of strong to severe thunderstorms during
the late afternoon and early evening. Confidence in this threat
remains low, as several failure points exist. First, guidance still
varies on the strength of the low and its speed, leading to
uncertainty in boundary layer moisture and instability.
Additionally, an earlier front in the day favors the threat being
displaced eastward from the CWA, and the front will be moving
quickly, potentially undercutting storms. If a severe thunderstorms
threat materializes, deep-layer shear vectors mostly parallel to the
front and the speed of the front itself will favor QLCS storm mode.
Steep low-level lapse rates will favor damaging wind gusts being the
primary threat, with a secondary threat being tornadoes for line
segments that can bow to the northeast given the orientation of the
0-3km shear vector. Southeastern Missouri is where a majority of
severe-favoring guidance supports this environment, with the threat
decreasing northeastward into southwestern Illinois.

The post-frontal airmass will be packing a punch and will send
temperatures free-falling through the evening and overnight hours.
This will allow for precipitation behind the front and associated
with the low`s deformation zone to transition to snow Sunday night
into Monday morning. As with the severe threat detailed prior, the
threat for accumulating snowfall is equally uncertain due to
differences among guidance in the handling of the surface low.
Additionally, moisture will become increasingly shallow as the front
departs the CWA, with model soundings showing varying degrees of
saturation within the dendritic growth zone (DGZ). Steep low-level
lapse rates may allow for enough instability to build beneath the
DGZ to lift moisture into the DGZ and increase ice crystal growth.
At the very least, SLRs looks to be below climatology. If
accumulating snowfall does occur, the best chances (50-60% per the
NBM) for at least 2" through Monday morning are north of I-70 in
Missouri and across west-central Illinois.

As Sunday`s system and impacts quickly move eastward, our attention
turns toward the anomalously cold air mass settling into the Midwest
in its wake. Deep northwesterly flow on the western periphery of the
departing upper-level trough will advect sub-freezing air into the
region Sunday night, with all guidance sources supporting lows well
below 32 degrees Monday morning for the entire CWA. In fact,
ensemble probabilities are at 80-90% that most locations along and
north of I-70 will fail to warm above freezing during the day
Monday. This will set the stage for even a cold night Tuesday night,
with the 75th percentile of Monday night`s low temperatures being
colder than the 25th percentile for Sunday night`s low among
ensemble guidance. This supports widespread values in the teens and
single digits across the region; though exactly how cold will depend
on how quickly winds can calm before shifting south-southwesterly
and how long skies can remain clear.

The south-southwesterly winds are associated with low-level ridging
passing through the Mid and Deep South. Guidance consensus is that
our anomalously cold airmass will be stubborn to depart the area,
leading to 70-90% chance of highs failing to crack 32 degrees for
our Illinois counties on Tuesday. Ensemble means and spreads support
temperatures continuing to warm through the remainder of the week,
despite multiple clipper-esque systems diving through the Midwest via
northwesterly flow.

Elmore

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 614 AM CDT Fri Mar 13 2026

West/northwesterly winds are expected to gust this morning into
at least early afternoon before subsiding later today into
tonight. VFR conditions are expected to prevail under scattered to
broken high clouds. Winds go calm to light/variable overnight,
then shift out of the south Saturday.

Maples

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory until 11 AM CDT this morning for Knox MO-Lewis MO-
     Marion MO-Shelby MO.

IL...Wind Advisory until 11 AM CDT this morning for Adams IL-Brown IL-
     Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Montgomery IL-Pike IL.

&&

$$

WFO LSX