Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

947
FXUS63 KLSX 211941
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
241 PM CDT Thu May 21 2026

.KEY MESSAGES...

- One more cool day is expected on Friday before temperatures
  return back closer to normal over the Memorial Day weekend.

- While there are chances of showers and a few thunderstorms each
  day through much of next week, there is no signal for any
  significant widespread rainfall or stronger thunderstorms.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 233 PM CDT Thu May 21 2026

Increasing clouds are expected tonight as low-level stratus
advects (and may expand) westward in easterly low-level flow.
Concurrently, mid/high level clouds will also advect northeastward
out of the central Plains. With the mostly cloudy sky overnight,
milder temperatures are in store with lows mostly in the mid to
upper 50s.

By early Friday morning, a weak midlevel shortwave trough will
approach from the Arklatex region. This feature will help develop
some shower activity, but the shortwave itself is a bit weaker and
farther southeast than 24 hours ago. In addition, the low-level
moisture convergence is weaker and more diffuse. This suggests
less widespread shower activity during the day on Friday, more
confined to southeast Missouri and southwest Illinois. Many areas
further northwest may not see any measurable rainfall. PoPs have
been reduced about 20-30% compared to yesterday`s forecast, with
chances ranging from 20-60% from northeast Missouri/west central
Illinois southeastward into southeast Missouri/southwest Illinois.
The signal for low clouds however is still quite strong with the
HREF probability of ceilings less than 3 kft AGL above 60% for
much of the CWA and above 80% for southeast Missouri and southwest
Illinois. These low clouds and northeasterly surface winds should
really limit the diurnal temperature range, with conditional
climatology for the month of May suggesting about an 8-11 degree
rise. In areas that see the most persistent low clouds, highs may
stay in the low to mid 60s. However, most should see highs top out
in the upper 60s to near 70 degrees, or another day with readings
about 10 degrees below normal for the date.


Gosselin

&&

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 233 PM CDT Thu May 21 2026

(Friday Night - Memorial Day)

While most of the holiday weekend should be dry, there is gradually
increasing low-level moisture/instability each day. There is no
semblance of organized mid/upper level forcing for ascent through
the weekend, but there are signs for the passage of multiple weak
midlevel shortwave troughs moving across the Mississippi Valley.
This may help develop scattered showers/weak thunderstorms each
day, with chances mainly confined to the afternoon/early evening
hours when diurnal instability is maximized.

Temperatures will also be on the increase this weekend, but highs
should stay mainly in the upper 70s to near the 80 degree mark.
While those values should be significantly warmer than much of
this week, they still would be just getting back closer to normal
for the end of May.



(Tuesday - Next Thursday)

The overall synoptic pattern across the CONUS does not change much
heading into the middle of next week with weak south/southwest flow
across the mid-Mississippi Valley. This means largely a continuation
of the sensible weather from the holiday weekend where temperatures
are likely near to maybe a bit above normal with daily chances of
showers/weak thunderstorms. Similar to this weekend, any activity
may be mainly confined to the afternoon/early evening hours.
Forecast highs were once again lowered a couple of degrees from
the NBM initialization during this time period after coordination
with the WPC. Forecast highs are still likely at least slightly
too warm due to the 60-day bias correction of the NBM. The air
mass next week looks closer to seasonal normals, with 850-hPa
temperatures nearing +15C (+1 to +2C) and at least some clouds and
chances of showers/weak storms as well. The signal for nighttime
temperatures being above normal is substantially stronger with
lows most likely in the 60s (5-8+ degrees above normal).


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1224 PM CDT Thu May 21 2026

MVFR ceilings from south-central Illinois will try and push
westward with the low-level flow into KSTL. This stratus may tend
to hang around then tonight, with ceilings lowering below 2 kft
AGL for KCPS/KSTL. This stratus should expand into the central
Missouri terminals closer to daybreak Friday. Rain chances
increase late in the period, but mainly south and east of the
terminals and the best chances are Friday afternoon. Therefore,
kept the TAFs dry other than KSTL, which goes out 30 hours. For
KSTL, added a PROB30 -SHRA group where MVFR visibilities may occur
in rain showers.

Gosselin

&&

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

$$

WFO LSX