Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

816
FXUS63 KLSX 070355
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1055 PM CDT Mon Jul 6 2026

.KEY MESSAGES...

- Seasonably warm and humid conditions continue through the
  weekend with scattered showers and thunderstorms mainly in the
  afternoons.

- The best potential for widespread rain comes Thursday night into
  Friday.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 247 PM CDT Mon Jul 6 2026

High pressure over the Great Lakes has brought a northeast flow
across our region, dropping temperatures and dewpoints to more
comfortable levels considering the time of year. Scattered showers
and thunderstorms have bubbled up across southern Missouri extending
eastward along the Ohio River. This is in an area of greater
moisture where the drier air hasn`t quite arrived yet. It`s also
being supported by a weak trough aloft with its center over northern
Arkansas, but with broader elongated troughing extending northeast
along the Ohio River. Showers and storms that develop here will be
developing in an environment with very little wind shear, so storm
organization will be difficult to come by. Heavy downpours and
lightning will be the primary threats, though a rogue downburst is
also possible with any healthier updraft. Due to the dry advection
further north, this activity is likely to be confined to the far
southern portions of our forecast area this afternoon.

As ridging over the Rockies expands eastward into the Midwest on
Tuesday, the weak trough in our vicinity will become further cut off
from the flow, wobbling around in the vicinity of the Mississippi
delta to lower Ohio River region. This will help hold temperatures
in the mid 80s, a couple of degrees below normal for July.
Additional shower and thunderstorm development is possible again
Tuesday afternoon, but will be dependent on where that upper low
wobbles off to. At the moment, guidance is favoring areas just south
of our forecast area, so convection in our area may be even more
limited on Tuesday than it is today.

Kimble

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 247 PM CDT Mon Jul 6 2026

Ridging continues to expand eastward across the center of the
country on Wednesday, but the pesky cut off low will remain stuck
near Cairo, IL on Wednesday. While temperatures likely tick up
another couple of degrees over Tuesday`s highs, the trough will keep
things a bit cooler than it would otherwise be. The warmest
temperatures will be in central Missouri, furthest from the
influence of the trough, where highs around 90 are forecast.
Additional showers and thunderstorms are expected in the vicinity of
the weakening trough, mainly over southeast Missouri into southern
Illinois.

As we head into Thursday, a shortwave trough tracking over the top
of the broad ridge is expected to finally kick out the cut off low.
That will open us up to a bit warmer temperatures, with most of us
topping 90 degrees Thursday afternoon. Humidity remains modest for
the time of year, but still enough to push the heat index up toward
100 degrees. This assumes we get significant sunshine, though. The
incoming shortwave may be accompanied by clouds and thunderstorms
which could hold back on the heat. NBM shows this uncertainty with
an interquartile range for high temperatures doubling from 2F on
Wednesday to 4F on Thursday. Northern areas closer to the track of
the shortwave trough have the better chance of seeing clouds and
thunderstorms hold temperatures back a bit. With a little better
shear available, thunderstorms on Thursday have the potential to
organize into an MCS, and if this occurs then a threat for damaging
winds could develop.

A cold front/outflow boundary will push south in the wake of
Thursday`s trough setting up the potential for additional storms on
Friday in the vicinity of that boundary. Again we couldn`t rule out
a damaging wind threat if storms can organize into an MCS. And with
the potential for storms to repeat in the vicinity of the boundary
there will be at least a low threat for locally heavy rain and flash
flooding as well. Low level moisture maximizing ahead of the
boundary will send precipitable water values up to around 1.9
inches. Current NBM POPs likely undersell the thunderstorm potential
a bit. We have strong confidence that the boundary will trigger
thunderstorms in our forecast area on Friday, but uncertainty in the
position of that boundary and timing of storms along it reduce the
overall POP at any one location. Up to 90 percent of low resolution
ensemble guidance produces rainfall across our area Thursday night
into Friday.

Ridging amplifies a bit more over the Colorado Plateau later this
week, with our area in the northwest flow on the eastern side of
this ridge. Thus we`ll have the potential to feel the heat expanding
from this ridge, but also are more likely to be affected by
shortwave troughs rounding the ridge and surface cold fronts cutting
back on the heat in the low levels. Friday`s front is likely to sink
southward this weekend, with the zone of convection along it sinking
southward as well. The further south it sinks, the greater the
potential for our area to see more sunshine and mix into some of the
hotter temperatures of the building ridge. NBM interquartile range
for high temperatures rises to about 7F by Sunday, reflecting that
uncertainty on cloud cover and mixing. On the upper end, we would be
looking at temperatures climbing back into the low to mid 90s.
Dewpoints, though, should remain modest by mid summer standards, as
we remain disconnected from a more sustained flow of moisture off
the Gulf. Some model guidance attempts to develop more extreme
dewpoints by Sunday into Monday, but I remain skeptical as this
would have to come largely through evapotranspiration. If the higher
end temperatures and dewpoints materialize, then we will see heat
index values climbing above 100 again. However, confidence remains
low (less than 20 percent) that we`ll see a period of sustained high
heat index readings locally. The greater potential for more extreme
heat will be further west in the Plains, closer to the center of the
ridge.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1051 PM CDT Mon Jul 6 2026

Light and variable surface winds are once again expected tonight.
Considering recent thunderstorms and added soil moisture, a few
outlying locations could develop patchy light fog, especially in
area around thicker vegetation and river valleys. Otherwise,
expect VFR conditions to persist. Tuesday bring another chance for
isolate showers and perhaps a thunderstorm. Support for this
activity shifts slightly southward with the highest chances over
southeast Missouri and southwest Illinois. Most terminals will
avoid this potential, though a brief shower or weak thunderstorm
cannot be entirely ruled out.

Maples

&&

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

$$

WFO LSX