Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

334
FXUS63 KLSX 071125
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
625 AM CDT Tue Jul 7 2026

.KEY MESSAGES...

- Temperatures will remain near to a few degrees above normal for
  early to mid July into the weekend.

- There is a chance for afternoon showers and thunderstorms today
  and Wednesday mainly south and east of St. Louis. More
  widespread thunderstorms are likely Thursday night through
  Friday night.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 420 AM CDT Tue Jul 7 2026

An upper level low is drifting east along the Missouri/Arkansas
border this morning.  This low will continue to drift east-northeast
through Wednesday.  A weak ridge of high pressure will continue to
produce light north to northeast flow today.  This northeast flow is
responsible for the more moderate temperatures and humidity over the
Mid Mississippi Valley over the past two days.  Guidance is
continuing to print out light QPF in the vicinity of the upper level
low this afternoon, and this looks reasonable given the isolated to
widely scattered convection which developed yesterday afternoon.
Unsure how far north and west to drag PoPs this afternoon; however,
forecast soundings suggest the relatively drier air advecting in
from the northeast will be enough to limit convection to areas along
and east of I-44 in Missouri and along and south of I-70 in Illinois
and the HREF paintball plot supports this idea.  Deep-layer shear
remains weak today, so severe storms are unlikely.  Expect
convection to dissipate in the evening with loss of daytime heating.
Thermodynamic and kinematic fields look very similar on Wednesday
as the upper low moves into the Ohio Valley, so PoPs are virtually
identical Wednesday afternoon.  Temperatures today will be very
similar to Monday`s in the mid to upper 80s.  Wednesday will be
slightly warmer in the upper 80s to low 90s as heights rise in the
wake of the upper low and weak warm advection develops on the
western side of the low level ridge.

Carney

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 420 AM CDT Tue Jul 7 2026

The upper level flow becomes quasi-zonal across the Mid Mississippi
Valley Wednesday night into Thursday.  Guidance shows a weak short
wave moving from the northern Plains into the Midwest late Wednesday
night into early Thursday.  This forces weak low level cyclogenesis
over Nebraska that enhances warm advection over Missouri and
Illinois. Traditional MOS guidance and the NBM agree that Thursday
will be the warmest day of the week. GFS 850mb temperatures push 22-
24C which mixes down to 95-99F at the surface. This is probably a
little too hot, with LREF IQRs generally in the 89-95 degree range,
and the NBM MaxT forecast in the 90-95 degree range fits this well.

The short wave also forces convection Wednesday night into Thursday
morning across Iowa that leaves a boundary near the Missouri/Iowa
border.  Guidance shows move convection focusing on this boundary
Thursday night, although it looks like there`s somewhat less
agreement in the location of the boundary, and just how strong the
forcing for convection will be.  However, there does appear to be
enough deep-layer shear for storms to become organized into a severe
MCS Thursday night, though where it develops and where it tracks
through the night is highly uncertain at this time.  Locally heavy
rainfall will also be possible with this system with a warm and
moist 30-40kt low level jet feeding it.  Friday`s temperature and
precipitation forecast is highly dependent upon what transpires
Thursday night and is very uncertain at this time.  Depending on if
an MCS develops and where it tracks, Friday could be relatively cool
compared to Thursday.  If the MCS tracks farther north and largely
remains out of our area, Friday could be very warm and humid again,
with highs potentially warmer than Thurday`s.  Guidance shows
another short wave moving through the Midwest Friday night into
Saturday, which produces another round of thunderstorms. Clouds and
potential rainfall suppresses temperatures on Saturday, but like
Friday this is conditional on where storms develop and track.

The forecast shifts back to hot and dry beyond Saturday as a strong
upper level ridge builds over the western 1/2 of the CONUS and
expands into the Midwest Sunday into next week.  Global guidance
keeps the Mid Mississippi Valley on the eastern periphery of the
ridge through Tuesday, and has the main thrust of the low level
thermal ridge over the Upper Midwest.  This may keep the most
extreme temperatures out of our area, but the pattern does support a
drier forecast with a potential for advisory-level heat index values
early next week.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 619 AM CDT Tue Jul 7 2026

VFR flight conditions and light northeast flow will prevail today.
There is a chance for widely scattered showers and thunderstorms
this afternoon and early evening, primarily across the eastern
Ozarks and southern Illinois, but there could be isolated
convection as far north as the St. Louis Metro area into parts of
central Illinois. Storms are not expected to be strong, but could
produce some gusty winds and low MVFR/IFR visibilities in brief
heavy rain. Convection should diminish rapidly after sunset. Winds
will become light and variable then turn to the east, then
southeast as a ridge of high pressure moves into the Ohio Valley.

Carney

&&

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

$$

WFO LSX