Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

910
FXUS63 KLSX 131201
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
701 AM CDT Mon Apr 13 2026

.KEY MESSAGES...

- Well above normal temperatures are expected to persist at least
  through Friday.

- Severe thunderstorms are possible Tuesday night, and again
  Wednesday afternoon and evening. Damaging winds and large hail
  are the primary threats both days.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 339 AM CDT Mon Apr 13 2026

The weather pattern continues to be controlled by a long wave
trough over the western United Sates and a ridge over the east.
This is producing deep southwest flow over the Mid Mississippi
Valley resulting in well above normal temperatures. Forecast
soundings show good mixing this afternoon to 850mb or slightly
higher with temperatures in the 14-18C range. This mixes down to
81-88 surface temps which agrees well with traditional MAV/MET
guidance as well as the deterministic NBM output. Insolation may
be limited a bit by clouds so I tended to lean a little lower on
that range. Some guidance members develop isolated showers today,
mainly over northeast Missouri and west central Illinois. This
looks to be in response to weak low level moisture convergence
produced by a broad 30-40kt low level jet. Forecast soundings show
a very strong inversion above the boundary layer, so deep
convection doesn`t look likely. However, low level lapse rates
below the inversion are very steep and there is a small area of
positive energy which could allow for some very shallow showers to
develop. Have therefore kept slight chance in the forecast in
northeast Missouri and west central Illinois today into the early
evening. Mild temperatures will continue tonight due to continuing
southwest flow with most locations only dipping into the mid to
upper 60s. In fact, there`s a chance that St. Louis and Columbia
may have their first 70+ degree lows since last September 15th
and August 19th respectively.

Carney

&&

.LONG TERM...  (Tuesday through Sunday)
Issued at 339 AM CDT Mon Apr 13 2026

The long wave trough over the western U.S. moves slowly east on
Tuesday and Wednesday which forces low level cyclogenesis over the
Great Plains.  A dryline pushes ahead of the surface low into
eastern Kansas and western Oklahoma Tuesday afternoon providing a
focus for convective initiation.  Current thinking is that
thunderstorms will develop over north central Oklahoma or eastern
Kansas and move northeastward off the dryline into Missouri during
the evening. GFS and RAP show 3000+ J/Kg SBCAPE Tuesday afternoon
extending into Missouri with 35-45kts of 0-6km shear for storms to
utilize.  However, the strong inversion remains in place over
Missouri Tuesday afternoon/evening, and guidance suggests strong
afternoon instability will decrease quickly in the evening.  It is
unclear whether storms which develop during the late afternoon will
have enough steam...so to speak...to make it into our forecast area
before weakening or even dissipating entirely.  The GFS is very wet
north of I-44 and west of I-55 Tuesday evening with its tendency
for grid-scale convective feedback to carry precip longer than
reality. The RAP is virtually dry in the same areas, and I tend to
feel this is more realistic as there will be little if any mid-
upper level support for convection over the Mid-Mississippi
Valley. The bottom line is that IF storms can make it into central
and northeast Missouri before the instability wanes during the
evening, some will probably be severe, with damaging winds and
large hail the most likely threats. However, I feel this threat is
very conditional at this time.

Wednesday/Wednesday night continues to look like the period which
will have the best chance for convection.  Mid-upper level support
will be much more robust as the trough moves from the Plains into
the Midwest. The surface reflection of the wave is forecast to
move from eastern Nebraska Wednesday morning to west central
Wisconsin by 06Z Thursday. This will push its associated weak cold
front into northwest Missouri Wednesday afternoon. GFS and ECMWF
are showing 2000+ J/Kg CAPE with 40-50kts 0-6km shear ahead of the
front Wednesday afternoon before convective initiation. The
convection reinforces the surface boundary and pushes into eastern
Missouri and southwest Illinois Wednesday night. Upper level
support from the eastward-moving trough should allow the storms to
survive into the nighttime. However, like Tuesday evening,
instability is forecast to diminish rapidly during the evening. As
a result, confidence in the eastward extent of the severe threat
is not high.

Some showers may linger into Thursday morning as the tail end of
the trough moves east of the Mid Mississippi Valley. Upper level
ridging builds back over the area by Thursday afternoon, but
southwest flow returns by Friday as another long wave trough digs
across the Rockies. This late-wek trough looks much more
progressive and higher amplitude than the first one with a
stronger cold front. Precipitation chances ramp up again Friday
afternoon through Saturday as the system sweeps through the Plains
and Midwest. Guidance members differ on the timing of the FROPA
through our area making the temperature forecast and severe threat
a very low confidence forecast. Some of the slower solutions
would keep Saturday`s temperatures well above normal in the upper
70s to mid 80s ahead of the front, and the 90th percentile SBCAPE
from the LREF approaches 2000 J/Kg. The faster solutions show a
much cooler and cloudy day with highs only reaching the 60s. The
front should be well southeast of the area by Sunday, with high
pressure building into the Midwest and temperatures near to a few
degrees below normal.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 643 AM CDT Mon Apr 13 2026

Areas of MVFR ceilings between 2500-3000 feet AGL will persist
across parts of southeast, central, and northeast Missouri through
at least 14-15Z this marooning. The these lower ceilings are also
expected to briefly spread into west central Illinois before
lifting. Additionally a small area of showers and thunderstorms
will continue moving northeast from central into northeast
Missouri and west central Illinois. The heaviest thunderstorm
cores will be capable of briefly reducing the visibility to 2
miles or less in moderate to heavy rain. Elsewhere and otherwise,
VFR flight conditions are expected to prevail today. Southwest
winds will increase to 15-20kts with gusts of 25-30kts. Current
thinking is that winds will stay gusty through tonight. However
low level wind shear conditions will be possible if surface winds
diminish this evening.



Carney

&&

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

$$

WFO LSX