Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

660
FXUS63 KLSX 270711
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
211 AM CDT Sat Jun 27 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms continue across the region
  through tonight, though the threat for flash flooding or severe
  weather is low.

- The first heat wave of the summer begins on Sunday. Dangerous
  heat index values over 100 degrees are expected to last at
  least through Thursday.


&&

.SHORT TERM... (Through Tonight)
Issued at 210 AM CDT Sat Jun 27 2026

A weak and nearly stationary front remains draped west to east
across the center of our forecast area this morning. To the south of
the front, light southerly winds have brought very humid conditions
northward, with dewpoints rising well into the 70s. To the north,
ENE flow has brought low clouds and slightly cooler conditions. In
some places, particularly where the front has sagged southward
overnight in central Missouri, areas of fog have developed.
Convective activity has focused on a few thunderstorm clusters
stretching from the southern High Plains eastward to the Ohio River
Valley. Our area has thus far been spared the more widespread
thunderstorms and heavy rainfall. However, with the front in the
vicinity we do still expect scattered convection over the next few
hours in particular, with this likely decreasing in coverage through
the morning hours. High precipitable water values (near 2 inches)
remain in place, so any thunderstorms will be capable of intense
local downpours. However, storm motions are expected to be quick
enough to prevent a significant threat of flash flooding. Because of
this reduced threat, the Flood Watch has been canceled.

The front will begin to lift northward today and especially tonight.
So long as it remains in the area we cannot rule out scattered
showers and thunderstorms along it. Convective activity likely picks
up in coverage after sunset tonight as a southwesterly low level jet
begins to push the front further northeastward. Again, locally heavy
rainfall is possible with this considering the very moist
environment, but the synoptic situation favors steady storm motions
which prevents a widespread flash flood threat.

Kimble

&&

.LONG TERM... (Sunday through Friday)
Issued at 210 AM CDT Sat Jun 27 2026

The surface front lifts fully northeast of our forecast area by
early Sunday, ending the rain chances and initiating a substantial
warm up. Upper level ridging builds over the Mississippi River while
troughing develops over the Western US and Northeast states. This
nearly stationary ridge allows for building heat on top of the
already high humidity levels in place. Temperatures are expected to
soar into the mid 90s on Sunday, with temperatures even a bit higher
over the following few days. When combined with the humidity,
dewpoints well into the 70s, the heat index will reach or exceed 100
degrees area wide beginning Sunday afternoon. Even higher heat index
values, up to as high as 110 degrees, are possible in spots, though
this will depend on subtle daily variations in humidity.

This period of high heat and humidity will be with us for a while.
We continue to have strong confidence that it will last through at
least Thursday, though it may last in some areas right through the
Independence Day weekend. Most guidance has the ridge weakening a
bit by the end of the week, though still persisting in some form
through the weekend. As the ridge weakens, daily chances for
thunderstorms start to creep back into the forecast providing a
potential break in the heat. We have issued a Heat Advisory for
nearly the entire forecast area for Sunday through Thursday as this
is the period we have the strongest confidence in dangerous heat.
For metro St Louis we have issued an Excessive Heat Watch as local
heat island effects make reaching heat index values of 105 or 110
more likely in this area. However, there`s still enough uncertainty
on those more extreme values to warrant only a Watch at this time.
The Advisory and any subsequent potential Warnings may eventually be
extended in time as confidence in the duration of the heat improves.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1036 PM CDT Fri Jun 26 2026

Light showers and some light drizzle will remain possible
through 09Z, particularly at UIN and the St. Louis area
airports. Otherwise ceilings are expected to drop to IFR
or LIFR by 08-09Z with visibilities between 1-4 miles in BR.
There will be some improvement by 16-19Z with visibilities
improving to VFR and ceilings improving to MVFR/VFR. There is some
chance for scattered shower or thunderstorm development again on
Saturday, but chances are too low (<30%) at this point to include
in any of the TAFS.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon Sunday to midnight CDT Thursday night
     for Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Knox MO-Lewis MO-Lincoln
     MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Francois MO-
     Sainte Genevieve MO-Shelby MO-Warren MO-Washington MO.

     Extreme Heat Watch from Sunday afternoon through Thursday
     evening for Jefferson MO-Saint Charles MO-Saint Louis City
     MO-Saint Louis MO.

IL...Heat Advisory from noon Sunday to midnight CDT Thursday night
     for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette
     IL-Greene IL-Jersey IL-Macoupin IL-Marion IL-Montgomery IL-
     Pike IL-Randolph IL-Washington IL.

     Extreme Heat Watch from Sunday afternoon through Thursday
     evening for Madison IL-Monroe IL-Saint Clair IL.

&&

$$

WFO LSX