Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

237
FXUS63 KLSX 150855
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
355 AM CDT Wed Jul 15 2026

.KEY MESSAGES...

- Very little changes have been to the temperature forecast,
  with near average temperatures and heat index values between
  95 and 105 degrees expected through the weekend, and
  potentially early next week.

- Scattered afternoon pop-up showers and thunderstorms are
  expected each afternoon today through Friday, with the best
  chances across the Ozarks today and tomorrow, and Illinois
  Friday. Bursts of heavy rain and lightning are the most
  likely hazards with these storms.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 245 AM CDT Wed Jul 15 2026

While dry conditions are in place early this morning, attention will
soon turn to the slow approach of rich moisture and a mid-level
vorticity maximum from the south over the next few days, as this
will bring increasing chances for afternoon showers and
thunderstorms. Water vapor imagery indicates that this feature is
currently located across central Mississippi and very slowly
drifting to the northwest, with a plume of moisture and other
smaller impulses ahead of it in southern Missouri. As the day
progresses, both of these features will nudge further north, and we
expect to see a round of scattered showers and weak thunderstorms
developing in the afternoon in the Ozarks and far southwest Illinois
as heating erodes a weakening capping inversion. With PWAT
values approaching 1.8 to 2.0 inches in these areas by that
time, the strongest cores may produce rain rates on the order of
1 to 2 inches per hour, which may cause localized flooding
issues in areas with saturated soils from recent rain.
Meanwhile, these storms will be developing within a regime of
relatively weak wind shear, but there is just enough easterly
mid level flow (25-30 kt) that cells will likely have at least
some modest forward motion. This also means that storms will be
moving from east to west, which is somewhat unusual for our
area. We also don`t expect severe storms, but can`t rule out
some wind gusts in the 30-40 mph range here and there.

Convective activity should wane a bit after sunset as we lose
afternoon heating, although a smattering of showers may persist
through the night. During the day though, the aforementioned vort
max is expected to continue moving northward and directly overhead,
along with the core of very rich moisture. As such, another round of
afternoon showers and thunderstorms is expected, likely with greater
areal coverage than today. Still, given the slow northward
progression of the upper low, the highest concentration of showers
and thunderstorms is still expected to occur across the Ozarks.
Meanwhile, very similar threats will exist with tomorrow`s storms,
including bursts of heavy rain, lightning, and occasional modest
downburst winds. Again, the threat of flooding appears low overall,
but storm motions may be slightly slower Thursday, and there are a
few locations in the Ozarks that are particularly sensitive to heavy
rain rates at this time and may experience localized minor flooding
impacts. Once again, the focus of this activity is expected to be in
the afternoon, but a few of the more persistent thunderstorms may
lingering the evening and overnight.

Otherwise, while very humid conditions are expected in the Ozarks
and southwest Illinois today due to dewpoints in the low to mid 70s
(and locally higher), and this humidity is likely to spread into
additional areas Thursday. Fortunately, temperatures are only
expected to top out in the upper 80s to low 90s, roughly average for
this time of year, which should keep heat index values in check.
Still, you can expect to see heat index values approaching 100
degrees in our warmest areas this afternoon. This is something that
will need to be monitored today, because if we do reach 100 degree
heat index values today, we may be in danger of reaching the 4-day
Heat Advisory threshold of 100+ degree heat index values as
temperatures are likely to rise slightly through the weekend. Given
that we are now in mid-July and have already see widespread heat, we
will refrain from issuing any headlines for now, and see how today`s
temperatures verify first.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 245 AM CDT Wed Jul 15 2026

By Friday, the subtle impulse partially responsible for Thursday`s
shower activity is expected to slowly pivot to the northeast,
carrying the focus of renewed showers and thunderstorms with it.
While the exact motion of such a small feature is somewhat uncertain
at this time range, the greatest rain chances are expected to shift
into Illinois, although we may see some activity in far eastern
Missouri near the Mississippi River as well. At the same time,
shower coverage is likely to wane across the Ozarks and central
Missouri due to a combination of increasing subsidence and drier
westerly flow. In any case, a similar round of scattered afternoon
pulse-type showers featuring brief heavy rain rates, lightning, and
occasional gusty winds appears most likely.

Over the weekend and into early next week, ensemble guidance
continues to indicate that the upper flow pattern will gradually
amplify, with a buildup of the longwave ride across the
intermountain west, and the development of a longwave trough across
the Great Lakes and eastern CONUS. While this process will
begin Saturday and Sunday with a digging weak shortwave trough,
this feature may be too far removed from our area for its
associated backdoor cold front to impact our area much, although
there are still some members that do bring such a feature into
our northern areas late Saturday, along with another round of
showers and thunderstorms. However, this is still very much in
the minority of solutions, and we have little confidence that we
will see much in the way of precipitation over the weekend.

Instead, given the higher probability that cold fronts will wash out
before they arrive over the weekend, confidence is increasing that
temperatures will, at a minimum, remain near seasonal averages, and
may even continue to rise by a degree or two each day. We should see
a slight decrease in dewpoints after Friday in western areas, but
without a notable cold front to push near-surface moisture out of
the area, high humidity is also expected to persist through the
weekend, with heat index values nudging slightly upwards into the
100 to 105 degree territory. Between Monday and Tuesday though,
there is an increasing signal in long-range ensemble guidance that a
deeper trough will dig into the Great Lakes, sending a more
noteworthy cold front south and through the area. Not only may this
renew chances for showers and thunderstorms, but this would also
likely put and end to any notable heat concerns by mid-week. There
is still a high degree of ensemble variance, though, particularly on
the timing of the initial cold front on Monday. A slower solution
would likely yield another warm day Monday (potentially the
warmest of the next 7 days), and add another day to a string of
100 to 105 degree heat index values, possibly even 5 days in a
row in some places. Again, temperatures and heat index values
will be evaluated today and tomorrow to determine if any
duration-driven headlines are needed.

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 349 AM CDT Wed Jul 15 2026

VFR conditions are expected to largely prevail at all TAF sites
through the 12Z TAF cycle. While there may be some patchy fog
and brief visibility reductions at river valley sites
(SUS/CPS/JEF) both at the very beginning and end of the period,
any visibility reductions and impacts are expected to be brief.

This afternoon, showers and thunderstorms are expected to
develop mainly across the Ozarks, and will most likely remain
south of all local terminals throughout this period. However, a
low probability exists (20% or less) for a rogue shower or
thunderstorm to develop along I-70 late this afternoon through
the night, but this chance is too low to include in the TAF at
this time.

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

&&

$$

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