Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

705
FXUS63 KLSX 021109
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
609 AM CDT Thu Jul 2 2026

.KEY MESSAGES...

- Hot and humid conditions continue through the Forth of July.
  Heat index values of 100 to locally 110 are expected each day.

- Scattered showers and thunderstorms are possible each day,
  mainly in the afternoons. The threat for severe weather or flash
  flooding is low.


&&

.SHORT TERM... (Through Friday)
Issued at 307 AM CDT Thu Jul 2 2026

The ridge which has brought our first extended stretch of hot
weather this year continues to gradually weaken and nudge to the
east. This morning it`s centered over the southern Appalachians,
with its influence still strongly felt into our region. We`ll have
another day of similar heat and humidity, though perhaps a degree
or so cooler than yesterday considering slightly cooler
temperatures aloft. Heat index values will mostly be in the 100
to 105 range with a few locations approaching 110.

Hot and humid low levels combined with slightly cooler
temperatures aloft will produce an accessible 2000 to 3000 SBCAPE
this afternoon. Looking upstream, yesterday storms developed in
northern Alabama beneath the ridge before drifting west through
Mississippi and west Tennessee before finally dissipating in
Arkansas a few hours ago. The remnants of this activity, both in
the form of a subtle upper level wave and surface level outflow
boundaries, may serve as the focus for additional thunderstorm
development this afternoon. With a southerly flow on the back side
of the ridge, the focus for this convection will lift north into
Missouri, potentially into our area. Considering weak wind flow
aloft, storms will be of the pulse variety with brief downpours,
gusty winds, and lightning the primary threats. However, I think
they may be a bit more numerous than most guidance suggests. We`ve
coordinated with neighboring offices to include a broader area of
low end mentionable thunderstorm chances this afternoon into the
evening.

The ridge continues to weaken and reorganize itself on Friday,
with the overall flow across the center of the country flattening
out into more of a zonal flow. The result for us will be little
change in air mass quality, but perhaps a bit more exposure to the
potential for thunderstorms. An MCS is expected to track west to
east across Iowa into northern Illinois, but it`s possible the
fringes of this activity reaches the northern portions of our
area. Even more likely is that outflow from this may serve as the
focus for renewed development in the afternoon. Either way, the
forecast for Friday remains the same: hot and humid with scattered
thunderstorms. The Storm Prediction Center does have the northern
portion of our area encompassed in a Marginal (level 1) outlook
with concerns for damaging winds from the MCS just to our north.
This risk is low enough that we do not plan to message this
locally at this time.

Kimble

&&

.LONG TERM... (Friday Night through Tuesday)
Issued at 307 AM CDT Thu Jul 2 2026

On Saturday, Independence Day, the ridge continues to reorganize
with the focus shifting west to the Rocky Mountains. This puts our
area in at least some degree of northwesterly flow aloft, with a
surface frontal boundary sinking southward out of Iowa. This front
will serve as a focus for additional showers and thunderstorms,
with thunderstorms possible area wide by afternoon. Temperatures
will again be seasonably hot in the low to mid 90s, with elevated
humidity (dewpoints still in the 70s). Although the threat of
thunderstorms and clouds from those do cause some uncertainty on
just how hot it will get, especially up north, we do have strong
confidence in heat index values topping 100 degrees once again. We
will need at least one more day of heat headlines of some sort.
After discussions with neighboring offices, the decision was made
to hold off on any extension of heat headlines for now. SPC has
again included us in a marginal (level 1) outlook for Saturday due
to the potential for storms to conglomerate into an MCS with a
greater threat for damaging winds if that were to occur. While
this is a legitimate possibility, the threat is low enough for now
that we do not plan to message it locally at this point.

The trend in 00Z guidance for Sunday is to favor the idea of a
more pronounced trough over the Great Lakes downstream of the
developing ridge over the Rockies. This pushes the cold front even
further south, with even ensemble means favoring northerly wind
direction as far south as St Louis Sunday afternoon. North of the
front there`s finally some break in the humidity, with dewpoints
potentially falling into the 60s. Ahead of it, it stays very
humid, but another round of showers and thunderstorms will likely
hold temperatures down a few degrees relative to Saturday. Thus
the likelihood of dangerous heat (Heat Index over 100) is lower on
Sunday and focused in the southern part of our area where the
frontal passage is least likely.

By Monday the front is likely to have cleared the entire forecast
area, though it will be washing out and becoming less defined with
each passing day of storms developing along it. Temperatures
behind the front will be closer to normal for this time of year,
in the upper 80s to near 90 for highs with less extreme humidity
than we saw earlier this week. Although current forecasts continue
to include chances for showers and thunderstorms each day through
the middle of next week, the recent trend of pushing the front
further south also shifts this daily threat of thunderstorms
toward the southern portion of our forecast area.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 607 AM CDT Thu Jul 2 2026

Light winds and a clear sky start the day, but by this afternoon
we`ll see more widespread cumulus developing at about 4-5000 feet.
Some of these are likely to bubble up into thunderstorms, but
confidence is too low on where this will occur to include this in
any TAF at this point. Storms that do occur will have heavy
downpours and gusty winds and are most likely between 20-24Z.

Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Warning until 10 PM CDT Friday for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Extreme Heat Warning until 10 PM CDT Friday for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX