Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

808
FXUS63 KLSX 131952
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
252 PM CDT Mon Jul 13 2026

.KEY MESSAGES...

- Expect several days of seasonable heat and humdity with highs
  climbing back into the 90s. Heat index values of 100 to 105
  are possible again from Thursday into the weekend.

- Most locations are expected to remain dry this week, with
  precipitation chances limited to portions of southern Missouri
  and Illinois.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 246 PM CDT Mon Jul 13 2026

Recent mid-level water vapor imagery reveals an anomalously strong
mid/upper-level ridge centered across the Upper Midwest, with a
surface high centered across IA this afternoon. Further to the south
and east, across the Deep South, nebulous pieces of mid-level energy
continue to slowly retrograde to the west under easterly flow. This
setup places the area under light easterly flow, with a lack of mid-
level energy nearby. Both of these variables are aiding in the
advection of a dry/less humid airmass than compared to our recent
one, which has resulted in a seasonable day across the bi-state
region. After sunset, surface winds are forecast to go calm and
variable with close proximity to the surface high. This, coupled
with a clear sky may favor the development of patchy fog,
particularly across northeast MO/west-central IL and river valleys,
where surface winds should be more consistently calmer. As the
mid/upper-level ridge remains parked where it is, a rinse and repeat
kind of day is on tap for Tuesday with highs in the mid/upper 80s
with a mostly clear sky.

By Tuesday afternoon/evening, some high-resolution guidance progs the
aforementioned pieces of mid/level energy retrograding into far
southern MO/IL. As a result, a minority of the members indicate
scattered thunderstorm development in this region while a majority
keep this part of the area dry. The unprecedented ridge aloft will
continue to result in strong subsidence across the area, which
should inhibit the development of convection. Although, with the
potential for subtle waves of mid-level forcing across southern MO,
there is currently about a 20% chance for an afternoon/evening pop-
up shower/thunderstorm across Reynolds, Iron, and Madison counties
with lower (greater) chances to the north (south).

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 246 PM CDT Mon Jul 13 2026

Long-range guidance indicates the ridge expanding eastward into the
Great Lakes region around midweek, which would gradually veer the
flow across our area from easterly to increasingly southerly. This
would lead to better warm/moist advection into the area while also
potentially allowing the retrograding mid-level energy to the south
to push further north within closer proximity to the region. As a
result, the current forecast indicates 20-50% chances for
thunderstorms on Wednesday and Thursday, generally south of the I-70
corridor, as clusters of energy propagate westward near southern
MO/central AR. Forecast soundings reveal a slightly weaker capping
inversion on Wednesday/Thursday than compared to Tuesday, mostly
thanks to greater low-level moisture, which aligns with the thinking
of increased chances for pop-up thunderstorms Wed/Thurs generally
across southern Missouri and Illinois. By later in the week, the
mid/upper-level ridge axis begins to shift westward into the
Intermountain West allowing longwave troughing across the northeast
to slide west also. An evolution like this would lead to the
potential for back door cold front(s) along with additional chances
for showers and thunderstorms into the weekend. Lastly, with
increasing low-level moisture thanks to persistent southerly flow
from midweek into the weekend, heat index values will be creeping
upward again. Analysis of the 00Z LREF indicates about a 30-50%
chance for heat index values >100F Thursday through the weekend.

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1209 PM CDT Mon Jul 13 2026

VFR conditions with light northeasterly/variable surface winds is
forecast to prevail at all terminals this package. Surface winds are
expected to go calm and variable after sunset with a mostly clear
sky prevailing. As a result, there is a weak signal for fog later
tonight, particularly in river valleys and across northeast MO/west-
central IL. However, with low confidence (20%) in this occurring, no
mention was included in this TAF issuance.

&&

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

&&

$$

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