Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

118
FXUS63 KLSX 042026
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
326 PM CDT Tue Aug 4 2026

.KEY MESSAGES...

- Isolated showers and thunderstorms are possible late tonight
  into Wednesday morning.

- More widespread thunderstorms are expected Wednesday afternoon
  and Wednesday night. A few storms may produce damaging winds
  and locally heavy rainfall. Isolated large hail and a brief
  tornado are also possible.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 316 PM CDT Tue Aug 4 2026

A cold front stretching through Iowa into southeast Nebraska will
drift into Missouri tonight.  The front and its low level baroclinic
zone will provide a focus for thunderstorm development through the
short term.  Could see some isolated convection creep into northeast
Missouri/west central Illinois even before 12Z Wednesday, although
all indications are that this convection will be relatively weak and
sparse over our area.  Models suggest more widespread development
Wednesday afternoon as a mid/upper level short wave trough moves
from the Great Plains into the Midwest.  The upper level wave will
produce broad-scale lift along with steepening mid-level lapse rates
to support afternoon convection. There`s still some uncertainty on
where convective initiation will occur, but most models are pointing
toward northwest or north central Missouri between 17-19Z.  Could
see 1500-2000 J/Kg CAPE Wednesday afternoon with 35-40kts of shear.
Could see a few supercells initially, but CAMs show individual
cells quickly merging into line segments and clusters.  Think the
primary threat will be damaging winds, but some hail will also be
possible. 0-1km helicity is also forecast to be 100+ m2/s2 so can`t
rule out a tornado or two as well.

The focus turns to potential for heavy rain on Wednesday night as 30-
35kt low level jet develops over Missouri. Deterministic guidance
shows moderate to strong moisture convergence along the low level
baroclinic zone on the nose of the jet, and all models print out
widespread QPF, mainly north of I-70.  HREF mean precipitable water
values are in the 1.8-2 inch range south of the front, and the 6hr
LPMM values of 2-3 inches with spots of 5+ inches.  However, 1 hour
flash flood guidance is 2+ inches, and it increases to 3 an 4+
inches at 3 and 6 hours respectively.  Given the environment,
kinematics, and the signals in the QPF, heavy rain is a definite
concern for Wednesday night, but the relatively dry antecedent ground
conditions should allow for a good deal of rain to be absorbed
before any flooding begins.  If the signals in guidance remain this
strong though, a flood watch may be needed for Wednesday night.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 316 PM CDT Tue Aug 4 2026

Medium range guidance shows a somewhat blocky pattern with a ridge
over the Desert Southwest, another ridge in the western Atlantic,
and a long wave trough sitting over the Midwest and Mississippi
Valley in between.  The pattern tries to become more progressive and
zonal late in the weekend, but there aren`t any obvious broad-scale
forcing mechanisms to move the surface front.  In this case, the
position of the effective front will probably be determined by
outflow from convection along it.  Temperatures will therefore be
difficult to forecast for Thursday into the weekend.  Current
indications are that Thursday and Friday will be relatively cool in
the low to mid 80s with clouds and intermittent showers and a few
thunderstorms.  However the 75th percentile of high temperatures
from the LREF is just under 90 degrees, which is certainly possible
if the front is farther north than expected.  The Bermuda High tries
to build back to the west into the gulf and the southern U.S. late
Friday into Saturday which would tend to bring southerly flow back
to the Mid Mississippi Valley, and push the surface front north away
from our area.  This will bring temperatures back into the upper 80s
to low and mid 90s by Sunday/Monday.  The prevailing southerly flow
will also bring higher humidity back to the Mid Mississippi Valley
and a threat for heat index values above 100 degrees.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1228 PM CDT Tue Aug 4 2026

VFR flight conditions and light southerly flow is expected to
prevail at least through this evening. May see isolated to
widely scattered showers and thunderstorms develop ahead of a
cold front late tonight across parts of central and northeast
Missouri into west central Illinois. Storms late tonight into
Wednesday morning are not expected to be particularly strong,
although some could briefly reduce the visibility to 3SM and
lower in heavy downpours. Another round of thunderstorms is
expected Thursday afternoon.

&&

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

&&

$$

SHORT TERM...Carney
LONG TERM...Carney
AVIATION...Carney