Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

692
FXUS63 KLSX 021852
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
152 PM CDT Sun Aug 2 2026

.KEY MESSAGES...

- Temperatures slowly rise to near seasonal averages early this
  week, with dry conditions expected.

- A cold front brings an opportunity for showers and
  thunderstorms late Wednesday and early Thursday, with lower
  chances later in the week.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 151 PM CDT Sun Aug 2 2026

The short term portion of this afternoon`s AFD will be on the
shorter side today thanks to the persistence of mild
temperatures and dry conditions for the next few days. Aside
from a modest warmup heading into mid-week, weather conditions
should be generally pleasant during this period.

Low cloud cover has slowly begun to scatter out across eastern
Missouri and Illinois on the back side of the departing low, but
many of these areas will continue to see more clouds than sun this
afternoon before finally clearing late in the day. For the rest of
the area, breezy north winds and mostly clear skies can be expected
today, with lowering wind speeds late in the afternoon and evening
as surface high pressure settles in. While the added sun will boost
temperatures back to near or slightly above 80 degrees this
afternoon, this is still almost 8-10 degrees below the daily average
for this time of year. Meanwhile, dewpoints have also dropped due to
persistent northerly winds, resulting in comfortable humidity levels.

Overnight, winds are expected to become nearly calm, and lingering
low level moisture may lead to some patchy fog development in river
valleys, particularly in the Ozark valleys that area already prone
to fog development. The depth/magnitude of low level moisture is not
particularly ideal for widespread fog, though, so we`d expect most
of this to be shallow and restricted to the most protected valleys,
where some instances of dense fog will be possible. Similar
conditions can be expected tomorrow afternoon thanks to the
persistence of the surface high pressure, with perhaps another
few degrees of warming from another day of ample sun.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 151 PM CDT Sun Aug 2 2026

The primary story Tuesday and Wednesday will be a slow increase
in temperatures, driven by the return of weak southerly low
level flow as the surface high slides just off to the east.
While these temperatures will be noticeably warmer on the heels
of our current, well below average values, this will be much
more typical of this time of the year with temperatures in the
mid 80s to low 90s and moderate humidity. Still, it likely won`t
be quite as humid as it otherwise could be, as we will hang
onto a modified airmass augmented by local evapotranspiration,
rather than a southerly feed from the Gulf.

Wednesday night though, a slowly digging upper trough will move into
the upper Mississippi River Valley, driving a weak cold front south
and into our northern areas sometime late Wednesday or early
Thursday. While there are typical timing differences among ensemble
members and clusters (deeper trough = faster, stronger front), this
is not out of the ordinary for this time range, and confidence in
the time window described above is growing. Meanwhile, moisture
pooling along this boundary is expected, boosting precipitable water
values perhaps into the 75th-90th percentile per ensemble means,
in spite of the poor Gulf trajectories. MUCAPE projections
ahead of this front also rise to around 1500-2000 J/kg Wednesday
afternoon, and drop down to around 500-750 J/kg overnight as
the front moves into our area. These parameters are not
particularly eye- catching but are supportive of a round of
showers and thunderstorms late Wednesday/early Thursday at a
minimum. So far, there is not much to support higher-end
threats, as modest shear/instability and the nocturnal timing
may limit the severe ceiling. There are some parts of the
pattern that support locally heavy rain (low level jet impinging
on a slow-moving front, with a large parallel component to the
mean flow), but moisture parameters are a bit lower than ideal
for this scenario, and the front is currently a bit more
progressive than you`d typically need. We also do not see a
notable signal for heavy rain in long-range indices (such as the
ECMWF Extreme Forecast Index), although there IS a stronger
signal just to the north in Iowa Wednesday. For now, it is
something to monitor, but the probability of notable severe
storms or heavy rain/flooding remains low overall.

Forecast confidence in additional precipitation chances the
remainder of the week are much lower, but it does appear that the
front will stall somewhere in the region, keeping the door open late
in the week. Meanwhile, the presence of this front will act as a
speedbump for our warming trend, which may take a few days to resume
as upper heights are slow to build. We also note widening ensemble
temperature spreads late in the week, in spite of a slow increase in
ensemble means, which indicates that while there is a slight
preference for warming, additional weak fronts/precipitation may
slow this down. It`s also notable that we are favored to remain in a
largely zonal, west-northwest flow regime through the end of the
week, which doesn`t strongly favor significant warming and also
leaves the area vulnerable to passing shortwaves.

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 1129 AM CDT Sun Aug 2 2026

VFR categories are expected to prevail for a majority of the 12Z
TAF period. Low clouds are finally scattering out around the St.
Louis metro area this afternoon, and this is expected to
continue. Overnight and early tomorrow morning, some patchy
river valley fog is expected in various locations throughout the
region, and this may periodically impact local terminals,
particularly JEF/SUS/CPS and to a lesser degree COU/UIN.

BRC

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

&&

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

&&

$$

SHORT TERM...BRC
LONG TERM...BRC
AVIATION...BRC