Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

992
FXUS63 KLSX 080235
AFDLSX

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

.KEY MESSAGES...

- Temperatures gradually warm through Thursday or Friday.

- The potential for showers and thunderstorms increases late
  Thursday through Saturday with at least a low threat for severe
  thunderstorms.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 145 PM CDT Tue Jul 7 2026

Broad surface high pressure remains centered near the Mississippi
River at the Iowa/Illinois border. The flow around this high has led
to the more modest humidity the past few days along with cooler
temperatures. Looking aloft, our region is in a weakness in between
two ridges. The ridge that brought our recent heat has weakened and
shifted southeast into the western Atlantic, while a new ridge has
strengthened over the Rocky Mountains. In the weakness in between we
see multiple weak lows stretching from the Rio Grande through the
Midsouth and to New England. The one nearest to us is currently
spinning near southeast Missouri making very slow progress toward
the Ohio River. With enough lingering low level moisture and cooler
temperatures aloft within the trough, instability has built up
with the heat of the day. With added support from the vorticity
aloft, we`ll see isolated showers and a few embedded thunderstorms
this afternoon mainly in southeast Missouri into southern
Illinois. With little to no wind shear to work with, any storms
will be of the pulse variety with primarily a threat for locally
heavy downpours and lightning. These should dissipate for the most
part within a couple of hours of sunset.

We`ll see a similar story for Wednesday, but with slightly warmer
temperatures and perhaps a little less coverage of showers locally.
The trough weakens and slowly pushes east while we get another day
of July sun working to modify the air mass in place. Temperatures
begin to approach 90 degrees, especially in central Missouri closer
to the influence of the western ridge.

Kimble

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 145 PM CDT Tue Jul 7 2026

A shortwave trough rounding the top of the western ridge will dip
southeast into the Upper Midwest on Thursday, sliding a surface cold
front southward into Iowa and northern Illinois. Our area should
remain south of the front on Thursday allowing for another day of
warming, into the low 90s. Thankfully, though, humidity remains
modest without a significant moisture connection to the Gulf,
meaning heat index values top out only around 100 degrees. As the
front continues to dip southward it will serve as a focus for
multiple rounds of thunderstorms over the coming days as
additional shortwave troughs track eastward in the vicinity of the
surface boundary. Wind shear does increase just enough to support
some storm organization with the potential for one or more
Mesoscale Convective Systems (MCSs) to develop mainly Thursday
evening and again Friday evening. Where these more organized
thunderstorms develop there will exist a greater threat for
damaging winds and locally heavy rainfall.

Each round of storms has the net effect of gradually shifting the
surface boundary southward, though how quickly this progression
occurs remains to be seen. This frontal positioning, and any cloud
cover associated with the rounds of thunderstorms, will impact the
temperature forecast Friday and Saturday. If the front doesn`t move
very quickly southward and we see strong sunshine, then Friday could
be just as hot or a bit hotter than Thursday. The latest forecast
assumes more cloud cover and a gradual southward push of the front,
leading to lower high temperatures each day through Saturday.

Late in the weekend the western ridge strengthens and expands into
the Northern Plains. This has the effect of pushing surface high
pressure southward through the Great Lakes and into the Ohio Valley
Sunday into Monday, further shoving the surface front southward.
With the front further south, the daily threat of storms also shifts
southward leading to a drier forecast as we go into early next week.
But with the ridge building to our north we`ll also see temperatures
begin to rise again. Guidance varies on how the ridge progresses,
with some eventually pushing the center of the ridge over our area.
Thus there`s some uncertainty on just how hot it will get. However,
confidence in high temperatures in the 90s increases each day
through the middle of next week, with NBM probability of 90+
reaching about 50 to 60 percent by Tuesday. However, with the
surface high nearby it will block access to richer Gulf moisture,
keeping humidity levels more modest for this time of year and
holding heat index values in check.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 931 PM CDT Tue Jul 7 2026

VFR conditions are expected throughout the 06Z TAF. While a few
weak showers have developed just southeast of STL this evening,
this activity is not likely to directly impact the terminal and
should diminish by the start of the period. Light winds are
expected overnight, with a low chance for shallow fog at river
valley sites (SUS/JEF/CPS), but given that fog struggled to
develop last night under very similar conditions, probabilities
remain too low to include in the TAF at this time.

VFR cumulus is expected again tomorrow afternoon, with another
limited opportunity for weak showers near St. Louis terminals in
the afternoon. However, once again the majority of this activity
is expected to remain southeast of the terminal, and the
probability of direct impacts to terminals remains too low (less
than 30%) for TAF mention at this time.

&&

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

$$

WFO LSX