Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

963
FXUS63 KLSX 131130
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
630 AM CDT Tue Oct 13 2026

.KEY MESSAGES...

- Hot and humid conditions continue with yet another chance to
  achieve record highs today.

- The first round of widespread showers and thunderstorms
  arrives late this evening into Wednesday with the potential
  for an isolated severe thunderstorm or two. The second round
  is expected to arrive late Wednesday into Thursday.

- A strong cold front brings much cooler and drier condition late
  week into the first half of next weekend.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 232 AM CDT Tue Oct 13 2026

Regional surface analysis reveals a cold front trailing a surface
low that was positioned over central Wisconsin as of 07z this
morning. The cold front stretched through the southern half of
IA, through NW MO, and into northern KS. South of the front,
temperatures were in the mid-60s to low-70s with dewpoints in
the in the 50s/60s.

This front is expected to slowly drift NW to SE this afternoon
through tonight, but before it does, another day of record heat is
expected. 850mb temperatures of around 20C will encompass the CWA
with deep mixing and southwesterly low to mid-level flow. Dewpoints
in the 60s/70s over the southern and central Plains will be drawn
northeast into the area today, which will be the biggest difference
from yesterday. Higher moisture will not only make it feel sticky,
it also brings to question how high temperatures will climb. MOS
guidance has been consistently too high and HREF ensembles favor low
to mid-90s. HREF probabilities show roughly 50-60 percent
probabilities at each climate site (KSTL, KCOU, and KUIN) to achieve
their respective record highs (see climate section). That being
said, the all-time monthly records may be a little harder to achieve
with KSTL running at around 10 percent to achieve this benchmark.
With that in mind, I took the highs down a notch (2-3 degrees).
Nonetheless, these temperatures are near the 90th percentile
even for late July and early August. Couple that with the
increase in moisture, peak heat indices of around 100 degrees
run along the MO River Valley and it is certainly notable for
mid-October.

The speed of the front has been another challenge, which will
dictate diurnal trends across the far northwestern section of
the CWA. The latest position and slow progress is still close
enough to this area that normal diurnal trends could be capped
by mid to late afternoon if isolated thunderstorms or cloud
cover streams in off development to the north and west. A vort
lobe at the western periphery of the Gulf ridge, rounds the edge
of the ridge atop the surface boundary tonight, when chances
truly begin to increase. The last couple CAMs updates have
bounced between nothing and isolated thunderstorms around 21z
over northeast MO. Chances look low considering broader ascent
remains west. The best chances hold off until after 00z this
evening.

Mid/upper vorticity begin to shift eastward from KS into MO
overnight, along with ongoing convection originating over the
eastern Plains and western MO. Some of the thunderstorms may be
locally strong to severe, supported by increasing shear (30-40
knots) and instability that peaks close to 2000 J/kg. However, mid-
level lapse rates are broadly below 6.5C with locally higher
pockets, and nocturnal trends taking over. Thunderstorms are
likely to become outflow dominant and lose instability to work
with, decreasing severe potential with eastward movement.
Another argument against better potential is the thinner CAPE
profiles seen in RAP model soundings than 24 hours ago.
Therefore, isolated damaging winds and hail cannot be ruled out,
but I think the chances decrease with time with the best
potential over central and northeast MO. Locally heavy rain is
the more likely outcome with PWATs of 1.5-1.75 inches, which is
2-3 standard deviations above normal. Widespread showers and
embedded thunderstorms will progress east-southeastward across
the region through at least Wednesday morning and early
afternoon. Widespread activity with trend downward Wednesday
late afternoon into early evening.

Highs today will largely be in the low to mid-90s, falling into the
upper 60s to low-70s tonight. Rain-cooled air will bring the first
push of relief Wednesday with highs in the mid-70s to mid-80s. Lows
Wednesday night will be in the 60s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 232 AM CDT Tue Oct 13 2026

There will be somewhat of a lull in rain chances heading into
Wednesday early evening before another round of widespread
showers and thunderstorm move through overnight into Thursday
morning.

The area of upper ascent that brings the first round will move east
into the Ohio Valley, as the second is almost a synoptic repeat of
the first. The difference here is in the mid to upper pattern, which
buckles slightly back to the north under the influence of the very
slight eastward shift in the upper low over the Rockies. Between the
two waves, isolated to scattered showers and thunderstorms remain
possible along the meandering surface boundary. By late Wednesday
evening into Wednesday night, mid/upper vorticity leans eastward
with another boost in upper ascent.

What has become more clear is the long range solutions in the
evolution of the upper low, which have come into better alignment.
This concerns the late Wednesday into Thursday morning timeframe,
when both ECM/GFS global guidance now show the upper low being
sheared out, spreading it between an amplifying Canadian trough, and
retrograding its southern fringes back to the southwest CONUS. The
impact here is for better support to be pulled slightly northwest
into NE, IA, and northern MO. By Thursday afternoon, the system
ejects into northern IL and southern WI, pulling a stronger cold
front southeastward. Much of the CWA remains in the warm sector,
though broken/overcast skies will limit surface instability,
especially north of I-70. With this in mind, as the upper support
continues to move east-northeast into the Great Lakes Region, the
potential for showers and thunderstorms will rely largely on frontal
convergence, becoming more scattered than widespread Thursday
afternoon and evening. One positive with this is that locally heavy
rain, resulting from thunderstorms, will shift between the two
primary episodes of higher rain chances. LPMM does have spots of 3
inches, but the fact that it comes in two rounds, varies in
location, and has good eastward movement, should mitigate flood
potential. Also consider that is has recently been very dry and river
levels are running lower with the recent dry stretch. I wouldn`t
expect much more than nuisance ponding under the heaviest rainfall.

By Thursday night, the front clears the area and brings much cooler,
below normal temperatures to the region. Long range guidance seems
to be making a compromise between cool temperatures and freezing
temperatures once advertised by the GFS. Dry conditions persist as
high pressure building in from the northern Plains and crosses the
area west to east between Friday and Sunday. Highs will be in the
60s Friday and Saturday. The coolest temperatures come Saturday
morning with the surface high overhead. Lows in urban areas settle
in the low-40s with outlying areas possibly as cool as the mid to
upper 30s.

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 624 AM CDT Tue Oct 13 2026

VFR conditions are expected to continue through much of the
period at all terminals. Showers and thunderstorms will approach
from the west late this evening. Scattered thunderstorms may
reach KCOU/KUIN/KJEF before 06z, becoming widespread after 06z.
Locally heavy rain, gusty winds, and visibility restrictions
are likely with their arrival.

Thunderstorms will make it to metro terminals a little later
with some uncertainty in their intensity by the time the
progress this far east. Heavy rain is still favored in the more
intense activity. MVFR conditions are likely with intermittent
IFR visibility and ceilings should thunderstorms maintain
greater intensity this far east.

&&

.CLIMATE...
Issued at 232 AM CDT Tue Oct 13 2026

Daily record highs and record warm lows continue today.
The daily records threatened are shown below.

Record High Temperatures:

October 13:
KSTL: 90/1899
KCOU: 95/1899
KUIN: 87/1975

Record High Minimum Temperatures:

October 13:
KSTL: 69/2008
KCOU: 69/1899
KUIN: 65/1935

October 14:
KSTL: 70/1899
KCOU: 67/2017
KUIN: 67/1920

In addition, all time monthly record high temperatures are
within range of being broken. The following are the October
monthly high temperature records at each site:

October Record High:
KSTL: 94 most recently on Oct 1, 2019
KCOU: 96 on Oct 7, 1939
KUIN: 96 on Oct 7, 1939

&&

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

&&

$$

SHORT TERM...Maples
LONG TERM...Maples
AVIATION...Maples
CLIMATE...Maples