Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

857
FXUS63 KLSX 141058
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
558 AM CDT Mon Sep 14 2026

.KEY MESSAGES...

- Unseasonably hot weather is expected this week with heat index
  values reaching 100-105F+ for some locations Tuesday into
  Thursday.

- There is a 10-20% chance for strong to marginally severe
  thunderstorms on Tuesday with the main threat being damaging
  winds. Beyond Tuesday, daily shower and thunderstorm chances
  (30-70%) will focus mainly across northern MO.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 306 AM CDT Mon Sep 14 2026

Recent GOES-19 mid-level water vapor imagery reveals a large scale
flow regime that consists of ridging centered across the Great
Plains with troughing on either side. Analysis of the latest
regional surface features reveals a surface anticyclone sliding
southward across WI with a surface low lifting northeastward into MT
early this morning. This places our area under easterly flow with
increasingly southerly flow to the west over the Great Plains. As
the features mentioned above continue to slide eastward, our region
becomes enveloped in deep southerly flow leading to strengthening
warm/moist advection. An axis of enhanced low-level moisture
convergence, aided by the nocturnally driven LLJ, will spark showers
and thunderstorms across western MO around 07-10z this morning. By
late morning, when this activity nears portions of northeast MO, it
will be offset from the core of the LLJ leading to a gradual
weakening/scattering of this activity. Beyond the low (20-40%)
chance of a scattered shower across northeast MO late this morning,
the remainder of the day is forecast to be dry across the area. The
most notable change to the sensible weather today will be increasing
humidity/temps with afternoon highs expected to reach the upper
80s/lower 90s for most locations south of I-70. These temperatures,
coupled with increasing moisture, will result in afternoon heat
index values in the 90s for most locations, potentially nearing the
century mark for portions of central MO.

The anomalously strong mid-level ridge centered across the Ohio
river valley Tuesday continues to strengthen, exceeding
climatological maximums for this time of the year. At the surface, a
cold front across the Upper Midwest gets sent southward reaching IA
later tonight. A combination of the surface anticyclone and the mid-
level ridge axis to the east, keeping us in deep southerly flow,
will both work to slow the southward progression of this front, as
it is expected to become quasi-stationary near southern IA. With
850mb temperatures +20C (99th percentile) and dewpoints in the lower
70s (also near daily maximums) in the warm sector (south of the
boundary), heat index values of 100-105+ are certainly possible on
Tuesday. The best chance for these values are generally along/south
of I-70 with decreasing confidence further north, closer to where
the effective boundary (greater rain chances/cloud cover) should be.
Forecast soundings indicate that some locations could reach
convective temperatures on Tuesday (becoming uncapped), which would
favor the chance for scattered thunderstorm development within the
open warm sector with the main threat being damaging wind gusts.
However, the anomalously strong ridge reinforcing subtle height
rises/subsidence across the area may work to limit the
coverage/strength of any convection. Currently, the 30-50% chance of
showers and storms Tuesday afternoon result in lower confidence
regarding temperatures across the area. The main takeaway is
locations that remain dry/cloud free will be unseasonably hot with
potentially dangerous heat. As things become more clear over the
next day, a Heat Advisory will need to be considered for portions of
the area where confidence increases in heat index values exceeding
105+ on Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 306 AM CDT Mon Sep 14 2026

This boundary maintains a close influence on the weather we
experience across the area most of the week and leads to a fairly
uncertain forecast. Along and to the north of this boundary will
feature abundant precipitation leading to afternoon highs in the 70s,
with anomalously hot/near record temperatures to the south.
Currently, it appears that far northeast portions of MO and points
to the north have the best potential to experience showers and
storms while also maintaining slightly cooler temperatures from
Wednesday into late week. Along/near this boundary there will be
rich column moisture (PWATs near 2") and a deep warm cloud layer
supporting warm rainfall processes and efficient rainfall
production. If northeast MO/west-central IL receive multiple rounds
of precipitation, something that remains uncertain, then heavy
rainfall may become a concern. Currently, the greatest chance for
heavy rainfall and flash flooding appears to remain across
Iowa/western MO through Wednesday. Beyond that, uncertainty
increases due to lack of consensus with guidance on where the
effective boundary ends up at later in the week. Temperature IQRs
for most of the area indicate unseasonably hot conditions may
continue into the weekend with spreads around 5-10 degrees centered
on temperatures near 10-15 degrees above average. By Sunday, IQR
spreads increase to 15-20 degrees due to cooler 25th percentiles,
indicating the potential is there for the return of cooler
temperatures. It is worth noting that even the 25th percentiles for
Sunday only return temperatures back to near average, illustrating
just how anomalously hot temperatures will be this week.

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 558 AM CDT Mon Sep 14 2026

A region of convection has formed across western MO early this
morning with slow progression to the east. The leading edge of this
activity is now approaching north-central MO with the majority of it
still centered across northwestern MO. Guidance continues to
indicate this convection weakening with eastward extent while the
more widespread activity lifts northeastward into Iowa late this
morning. As a result, confidence in impacts later this morning at
KUIN remains low (20%), so no mention was included in this TAF
issuance. Short term trends of this activity will need to be
monitored for KUIN as the convection evolves across northern MO over
the next few hours. Easterly surface winds around 10-12kts slowly
veer southeasterly today eventually becoming southerly by tonight.
Some gusts of 20-25kts are most likely across northeast MO/west-
central IL this afternoon into the evening.

&&

.CLIMATE...
Issued at 220 PM CDT Sun Sep 13 2026

Daily record high temperatures may be threatened for both St. Louis
(KSTL) and Columbia (KCOU) this week. NOTE: Records at Quincy (KUIN)
are not shown below due to cooler temperatures forecast:

            9/15        9/16        9/17
KSTL     101/1939     98/1954     97/1931
KCOU  101/1893     99/1954     98/1895

&&

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

&&

$$

SHORT TERM...Peine
LONG TERM...Peine
AVIATION...Peine
CLIMATE...Gosselin