Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

630
FXUS63 KLSX 081100
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
600 AM CDT Wed Jul 8 2026

.KEY MESSAGES...

- Seasonably warm temperatures continue today, and scattered
  showers and thunderstorms are possible, mainly south and east of
  St. Louis.

- More widespread thunderstorms are expected Thursday through
  Saturday. Some storms could be severe Thursday and Friday
  afternoon and evening. Additionally, locally heavy rainfall will
  be possible.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 330 AM CDT Wed Jul 8 2026

An upper level low near the confluence of the Mississippi and
Ohio Rivers will continue to produce scattered showers and
thunderstorms for southeast Missouri and southern Illinois today.
The low will drift northeast and weaken, eventually opening into a
more progressive wave this evening. This will bring the chance
for convection associated with this system to an end for our area.
Temperatures today will be a few degrees warmer than Tuesday,
except over southeast Missouri and southern Illinois due to more
extensive cloud cover and scattered convection associated with the
upper low. The next upstream short wave is already producing
convection over the northeastern Great Plains into the Upper
Midwest. The wave will dig farther into the Midwest today, and
then the next behind it will move into the Midwest late tonight,
further amplifying the upper flow. Guidance shows another round of
convection over eastern Nebraska and Iowa, that moves into
northwest Missouri this evening. The convection will continue
moving east overnight, and could reach central and northeast
Missouri before 12Z Thursday morning, although it should be weak
by that time and coverage may be limited.

Carney

&&

.LONG TERM...  (Thursday through Tuesday)
Issued at 330 AM CDT Wed Jul 8 2026

Latest guidance suggests tonight`s convection will generate an MCV
which will track across the area on Thursday.  Additionally, the
composite outflow/surface front will drift across northern Missouri
into central Illinois during the afternoon and provide a focus for
convective development.  Temperatures in the low to mid 90s along
with dew point temperatures in the low to mid 70s and steepening
lapserates are forecast to produce very unstable conditions with
CAPE in excess of 2000 J/Kg.  Guidance also shows increasing deep-
layer shear up to around 35kts which would support organized
convection.  Think the most likely scenario is that thunderstorms
develop during the afternoon in the vicinity of the MCV/composite
cold front over central or northeast Missouri and get organized into
a broken line which moves quickly east-southeast.  Damaging winds
are the most likely threat, though some large hail is also possible
given the CAPE profiles in model soundings.

Think the severe thunderstorm threat should end during the evening
as instability wanes.  However, the low level boundary looks like it
will remain draped over our area, most likely across the Ozarks, but
this is uncertain.  Models show a west-southwest low level jet
developing during the evening which rides over the boundary
producing moderate to strong moisture convergence.  Convection is
therefore likely to redevelop in the vicinity of the boundary and
possibly train along it which would pose a heavy rain threat.

Friday`s weather continues to depend heavily on convective trends
Thursday night.  However, current thinking is the boundary will remain
over our area, possibly drifting northward through the day as
southerly flow increases ahead of another wave.  The GFS develops
2000+ J/Kg of CAPE during the afternoon coincident with 30+ kts of
shear which will produce another round of thunderstorms Friday
afternoon and evening which could be severe.

The long wave upper level ridge over the western U.S. begins
strengthening and building east Friday night into Saturday.  This
will eventually push warmer air aloft into the Mid Mississippi
Valley and finally cap the low levels.  Additionally, the downstream
long wave over the eastern U.S. will drag a drier airmass into the
Great Lakes and Midwest. This will turn the low level flow over our
area to the northeast and finally the surface boundary south.
However, it`s unclear how quickly this will happen.  Guidance PoPs
have increased Saturday and Sunday as the models build the ridge
eastward more slowly in the latest runs.  Additionally the LREF
cluster analysis is showing variance in the position and amplitude
of the ridge as it strengthens this weekend.  This lends a great
deal of uncertainty to the forecast for Saturday and Sunday,
particularly across the Ozarks where the boundary would likely
linger for the longest time.  While PoPs now linger into Sunday,
Monday and Tuesday continue to look warm and dry under the influence
of the upper level ridge.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 557 AM CDT Wed Jul 8 2026

VFR flight conditions are expected to prevail through Thursday
morning. Widely scattered thunderstorms are possible this
afternoon and early evening, generally south and east of St. Louis
in proximity to an upper level disturbance. The strongest storms
may produce gusty winds and MVFR/IFR flight conditions in brief
heavy rain. Additionally, there is a slight chance that
thunderstorms which develop over the Great Plains this evening may
reach parts of central and northeast Missouri between 10-12Z
Thursday morning. However, confidence is too low at this point to
mention in central Missouri terminal forecasts.

Carney

&&

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

$$

WFO LSX