Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

509
FXUS63 KLSX 261651
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1151 AM CDT Fri Jun 26 2026

.KEY MESSAGES...

- Periods of showers and thunderstorms continue through this
  evening. The primary threat will be flash flooding, though a low
  threat for severe thunderstorms also exists.

- Hot and humid weather builds this weekend, with excessive heat
  lasting through much of next week.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 252 AM CDT Fri Jun 26 2026

A stationary front remains parked across the middle of our forecast
area this morning, roughly in the vicinity of interstate 70.
Southerly flow continues to push moisture toward the boundary while
multiple ripples in the jet stream aloft feed pockets of showers and
thunderstorms from the Central/Southern Plains to the Ohio Valley.
With so many pockets of ongoing convection, high resolution guidance
is less reliable than normal in determining the timing of rain
chances over the next 12 to 24 hours. However, the primary focus
will be along and south of the stationary front. Heavy rainfall and
potentially flash flooding will be the dominant threats today. HREF
average precipitable water values climb to 2 inches or more
indicating that when it does rain it will be very efficient at
dropping heavy rainfall. As storms develop into one or more
convective complexes, localized training will provide the best
opportunity for flash flooding. The Flood Watch continues through
7PM.

The severe weather threat is a little more nebulous. While there`s
plenty of low level moisture to work with, daytime heating is more
uncertain with so many clouds and showers around. With at least some
sunshine, moderate instability will develop south of the front. Wind
shear is also modest, with only about 25KT of deep layer shear
available, sufficient for MCS development and maintenance but
somewhat weak for supercells. However, MCVs have a tendency to
locally enhance instability and shear. One such MCV is exiting
eastern Kansas early this morning and will be moving through the
southern portion of our forecast area around midday or early
afternoon. If sufficient destabilization occurs ahead of it, this
could reinvigorate and provide a more focused threat for
thunderstorms. Damaging winds and perhaps a tornado or two would be
the primary severe weather threat if this occurs.

A trough moving out of the northern Rockies tonight into Saturday
will finally provide the push needed to get the stationary front
moving again. It will gradually lift northeastward as a warm front,
with additional rounds of showers and thunderstorms possible along
it tonight and Saturday. These rounds are a little less certain,
though. High resolution guidance has less coverage of convection
tonight and Saturday than does the lower resolution guidance.
Considering the continued very moist environment, the Flood Watch
may need to be extended if confidence improves.

Kimble

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 252 AM CDT Fri Jun 26 2026

After the warm front finally lifts north on Saturday, we move from
the moistening stage of the forecast to the broiling stage. While a
trough digs into the Northwestern US, a ridge develops downstream
over the Mississippi River. From 18Z Saturday to 18Z Sunday, 850MB
temperatures rise locally by about 5C initiating a strong warm up.
With the upper ridge centered near our area, we`ll feel the full
effects of this building heat. There`s strong agreement in guidance,
as noted by the NBM interquartile range of only 2F Monday and
Tuesday, with highs forecast in the upper 90s. One spoiler we often
look for is the potential for ridge running shortwaves to bring
clouds and showers which hold back temperatures on the northern side
of the ridge. But at this point there doesn`t seem to be much
potential of that with the ridge center nearly overhead and the
storm track further north across the Upper Midwest. Guidance is also
in strong agreement on a dry forecast underneath this ridge, with
precipitation chances near zero Sunday through Wednesday. A look at
forecast soundings shows that while instability does exist in the
hot and humid air mass, a substantial cap will prevent convection.

The combination of building heat and continued high humidity will
lead to several days of heat index values of 100 to 110 degrees. It
is expected that at least a Heat Advisory will be needed as early as
Sunday, with the potential for Excessive Heat Warning criteria to
also be met. The core of the heat will be from Sunday through
Thursday, though there`s not a clear end date for the heat. Most
guidance has the ridge ever so slightly breaking down in one form or
another by the end of the week with better chances for convection to
provide some rain and heat relief. However, without a clear break
down of the ridge or a strong cold front, we don`t have much
confidence on when this heat wave will end. NBM interquartile range
for high temperatures triples from 2F early in the week to 6F next
weekend, indicating that growing uncertainty. Heat relief is
possible as early as Friday, but alternatively the heat could last
through the Independence Day weekend.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1150 AM CDT Fri Jun 26 2026

Showers and occasional thunderstorms will continue to impact local
terminals periodically through the remainder of the afternoon and
potentially into the evening. While initial activity will be
generally weak, occasional lightning strikes will be possible.
Some stronger thunderstorms with more frequent lightning, heavier
rain, and occasional strong wind gusts will be possible from mid
afternoon through early evening, impacting primarily I-70 corridor
terminals (COU/JEF/STL/SUS/CPS). This activity is expected to
shift south of all terminals by late evening but a few showers may
linger longer.

Otherwise, persistent low clouds are expected just north of I-70
from the start of the period through mid-day tomorrow, with MVFR
ceilings at a minimum, and the potential to drop as low as LIFR at
times overnight and tomorrow morning, particularly at UIN. Fog is
also possible in these areas overnight as well.

BRC

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 7 PM CDT this evening for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Pike MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

IL...Flood Watch until 7 PM CDT this evening for Bond IL-Calhoun IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Pike IL-
     Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX