Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

506
FXUS63 KLSX 061132
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
632 AM CDT Mon Jul 6 2026

.KEY MESSAGES...

- Expect seasonably warm weather this week, with highs near
  normal through Wednesday, and slightly above normal Thursday.

- There is a chance for thunderstorms today through Wednesday,
  mainly in areas from St. Louis and to the south and east.

- The best chance for storms this week will be on Thursday night
  into Friday as a front stalls over Missouri and Illinois.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 400 AM CDT Mon Jul 6 2026

Early morning water vapor imagery is showing a short wave trough
digging into the Mississippi Valley. RAP analysis is indicating
several vorticity maxima rotating around the axis of the wave, and
it appears that most short-range guidance is latching onto these
features to kick off scattered convection once again today.  Best
chances for thunderstorms should be across southeast Missouri this
afternoon, along and just ahead of the trough axis where lift will
be maximized. However, GFS and RAP are showing as much as 1000-1500
J/Kg CAPE back as far as central Missouri into west central Illinois
with very little if any CINH.  Could see isolated convection back
into these areas as well this afternoon.  Soundings indicate little
if any deep-layer shear, so pulse convection will be the mode of the
day.  A few storms will probably linger into the evening similar to
Sunday evening, but should finally dissipate before midnight.

The consensus from guidance is that the northern end of the short
wave will move east while the southern end closes off leaving a low
near the Missouri/Arkansas border today.  The low drifts east-
northeast through Tuesday ending up over far southeast Missouri by
00Z Wednesday.  The low will once again provide broad-scale lift to
promote convection Tuesday afternoon, and the environment will be
similar to today`s with modest instability and weak shear.  Think
convection will mostly be confined to east central and southeast
Missouri into southern Illinois which will be in closer proximity to
the low.  Lastly, temperatures for today and Tuesday continue to
look like they`ll be very similar to Sunday`s readings in the mid to
upper 80s as there will be little change in the pattern through then.

Carney

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 400 AM CDT Mon Jul 6 2026

The closed upper level low begins opening up on Wednesday, moving
east into the Lower Ohio Valley by 00Z Thursday.  GFS and ECMWF
continue to produce QPF on the western side of the low across
southeast Missouri and southern Illinois Wednesday afternoon, so
have continued chance PoPs in these areas.  The upper flow becomes
more zonal in the wake of the low for Thursday and Friday.  Both the
GFS and ECMWF show a weak short wave moving across the Midwest on
Thursday in the zonal flow which forces convection across Iowa and
Wisconsin/northern Illinois.  The environment looks favorable for
MCS development, and this system could move into northern Missouri
and central Illinois Thursday night.  The remnant boundary would be
a focus for continuing convection on Friday.  Therefore our highest
chances for rain will be in the Thursday night-Friday night
timeframe.  However, the initial short wave looks suspiciously like
it`s developed by grid-scale convective feedback in the models, so
I`m skeptical of the deterministic solutions.  An examination of the
LREF for Thursday night when we have our highest PoPs (60-80 percent
in many locations) shows around a 60/40 wet/dry split among the
members where the deterministic guidance shows the highest QPF.
Additionally the  probability distribution leans toward less than
0.20 inches of rainfall.  This all adds uncertainty to the
precipitation forecast for later in the week, but there could be at
least 2 or 3 rounds of thunderstorms if the deterministic models are
correct.

There`s a good deal of uncertainty in the forecast for Saturday and
Sunday as the flow aloft becomes highly amplified with a strong
upper level high building across the western 1/2 of the CONUS.  Our
local weather will depend greatly on how far east the ridge builds,
and any potential ridge running short waves that dive into the
Midwest if we stay on the periphery in northwest flow.  Current
indications are that temperatures will stay just above normal with
chances for thunderstorms both days on the eastern side of the
ridge.  However the ridge could move farther east into the
Mississippi Valley in which case temperatures could rise well above
normal by Sunday.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 624 AM CDT Mon Jul 6 2026

Scattered showers and thunderstorms will be possible again this
afternoon and evening, mainly along and south of I-70. Wind gusts
to 30-40kts and brief heavy downpours reducing the visibility to 1
mile or less will be possible with the strongest storms.
Otherwise, VFR flight conditions and light northerly flow is
expected through the period outside of thunderstorms.

Carney

&&

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

$$

WFO LSX