Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

610
FXUS63 KLSX 141747
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1247 PM CDT Tue Jul 14 2026

.KEY MESSAGES...

- Seasonably warm temperatures are expected through the end of
  the week, with increasing humidity and heat index values
  approaching 100 to 105 degrees Thursday and Friday.

- Chances for scattered afternoon pop-up showers and
  thunderstorms are increasing both Thursday and Friday
  afternoon (30-60%). While plenty of dry time is expected both
  days, these showers may produce brief heavy downpours.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 202 AM CDT Tue Jul 14 2026

As we await another round of high humidity and pop-up
showers/thunderstorms later in the week, at least one more day of
typical summer-like conditions is expected area-wide today. This is
thanks to the persistence of surface high pressure draped
across the Mid-Mississippi Valley, along with an anomalously
deep upper level ridge to our north. While the latter feature
will drive dangerous heat across the Northern Plains, Upper
Mississippi Valley, and Great Lakes regions, temperatures
locally are expected to remain very near seasonal averages for
mid July (upper 80s to near 90). Dew points are expected to
creep upwards this afternoon as higher surface moisture to our
east is caught up in easterly low level flow, but strong
subsidence aloft should prevent showers and thunderstorms from
developing locally. The primary impact of these increasing dew
points is expected to be on the heat index, which may rise into
the upper 90s to near 100 degrees in a few locations this
afternoon, particularly in southwest Illinois.

After another quiet night with light winds and mostly clear skies,
tomorrow is expected to be very similar in most areas, with only
subtle changes to the synoptic flow pattern and local sensible
weather. However, we have maintained a 20-50% chance of showers and
thunderstorms across the Ozarks, as deeper moisture is expected to
drift slightly further north, and the southern fringes of the upper
ridge and subsidence are both expected to weaken very slightly.
While there will be a lack of notable forcing mechanisms, we
may get just enough afternoon heating to produce a few pop-up
showers or weak thunderstorms in our southernmost areas, capable
mainly of brief heavy downpours. While we don`t expect these
storms to be widespread or long-lived enough to pose a
significant flood threat, very high PWATS (1.8-2 inches) and
deep warm cloud layers will support efficient rain rates. In
spite of this, most areas will remain dry, and even where
showers occur there will be plenty of dry time as well. We may
also see a few areas with an afternoon heat index near 100
degrees, but temperatures are expected to remain near seasonal
averages.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 202 AM CDT Tue Jul 14 2026

While we still do not expect an area-wide washout late in the week,
the chance for afternoon pop-up showers and thunderstorms does
appear to be increasing Thursday and Friday, resulting in an
increase in precipitation probabilities to the 30-60% range in many
areas both days. This is essentially a continuation of the trend
described in the short term discussion regarding Wednesday`s
shower/thunderstorm potential, as the upper ridge is expected to
gradually weaken, and deep moisture is expected to slowly drift
further and further north. Between the weakening subsidence aloft
and anomalous moisture (PWATs of 1.9-2.1 inches) moving directly
overhead, there is an increasing signal for diurnally-driven showers
and thunderstorms across a broader area Thursday afternoon, although
the Ozarks continue to be slightly favored for the greatest
coverage. Again, while very weak wind flow aloft and a lack of large-
scale forcing mechanisms limits the threat of prolonged heavy rain
or strong/severe thunderstorms, even brief pop-up showers will be
capable of heavy rain rates (1-2 inches/hour), which may be a local
concern in areas that have seen recent flooding. Still, plenty of
dry time is expected due to both the strong diurnal component (rain
is heavily favored from early afternoon to late evening), and the
scattered nature of this activity.

A similar setup is expected Friday, although most ensemble members
push the deepest moisture and highest precipitation chances
slightly northeast and into Illinois and right along the
Mississippi River, with building heights and subsidence nudging
back into the area from the southwest. Where these showers
develop, similar threats will exist (brief heavy downpours,
lightning), with showers being heavily favored in the afternoon.
Again, plenty of dry time is expected both before showers
begin, and in between them.

Forecast confidence decreases Saturday onward, as the upper ridge is
expected to retrograde slightly westward, with a weak trough digging
into the Great Lakes. This opens the door for weak back-door cold
fronts to dip into the area, but there is very little member-to-
member agreement on the timing of any such features. This is
producing much more variance in temperature/precipitation forecasts
in the extended period, although we do note a very slight trend
toward moderating temperatures and a reduction of PWAT anomalies
Sunday onwards, and ensemble mean precipitation chances do shift
eastward and lower substantially Saturday onward. Given the
potential for at least a modest forcing mechanism we can`t rule out
more chances for precipitation late in the period, but very little
confidence exists in the specifics at this stage.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1245 PM CDT Tue Jul 14 2026

VFR conditions with diurnal cumulus around 4kft are expected
for a majority of the period with the exception of some patchy
fog that is possible tonight before eroding after sunrise. The
most likely location of fog formation is expected to be in river
valley locations (KSUS, KCPS, and KJEF) and across portions of
northeast MO/west- central IL (KUIN). Light easterly winds are
forecast to quickly fade to calm and variable after sunset
lasting through the night until light easterly winds return
later tomorrow morning.

&&

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

&&

$$

SHORT TERM...19
LONG TERM...19
AVIATION...Peine