Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

661
FXUS63 KLSX 221114
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
614 AM CDT Fri May 22 2026

.KEY MESSAGES...

- Cool, cloudy conditions are expected today, with a few showers
  mainly along/south of I-44. A better chance (40-70%) for
  showers and a few weak thunderstorms exists late tomorrow
  through early Sunday.

- Near or slightly above average temperatures are favored for
  Memorial Day, with a modest potential (20-40%) for showers,
  again mainly along/south of I-44.

- Slightly above average temperatures are favored Tuesday onward,
  with slowly increasing chances for afternoon showers and a few
  thunderstorms.


&&

.SHORT TERM... (Through Sunday)
Issued at 352 AM CDT Fri May 22 2026

Today through Sunday is generally expected to be influenced by the
slow eastward progression of a northern-stream shortwave trough
across the northern Plains and upper Mississippi Valley, which will
phase with a series of subtropical impulses from the southwest at
various times. The latter waves are expected to drive a slow
northward push of Gulf moisture, which will manifest initially as
low clouds today through tomorrow night, along with periods of
showers this afternoon and again late tomorrow through Sunday. While
thunderstorms will occasionally be possible, particularly late
Saturday, the potential for strong or severe storms appears to be
rather low.

The first of these impulses is clearly evident in GOES water vapor
imagery early this morning centered near Texarkana, and this feature
will slowly move northeast and into SE MO/SW IL through the day. As
this occurs cloud cover will steadily increase, and we will likely
see a few showers and perhaps a rumble of thunder or two this
afternoon along/south of I-44 in MO and I-70 in IL. Considering that
these storms will be elevated above a cool stable later, with only
very modest MUCAPE and weak wind fields above it, it will be
difficult to muster much more than a stray lightning strike here and
there. Otherwise, expect another relatively cool day as winds remain
generally easterly and clouds continue to limit heating.

Showers will move off to the northeast by late evening, but low
clouds are expected to persist through the night, and there is some
potential for this low stratus to lower into fog in a few places due
to the very light winds and high humidity. This would be most
likely across central and southeast Missouri, where RRFS and HREF
probabilities for 1 mile or lower visibilities of 20-40%. These
probabilities are not particularly high and in most areas this is
more likely to remain a low stratus deck rather than fog, but
there is enough of a signal that we have added some mention of
patchy fog to the forecast.

During the day Saturday, slowly building heights aloft in the wake
of the passing shortwave should result in a modest boost in
temperatures, although continued weak low level flow and persistent
cloud cover will limit warm air advection and afternoon heating,
respectively. While it will be noticeably warmer, the latter factors
will likely cap our temperatures in the mid 70s to low 80s.

Meanwhile, precipitation chances will remain minimal until the next
subtropical shortwave arrives from the southwest late Saturday. This
feature will be similar to its predecessor, but most guidance
carries it a bit further north, with deeper moisture, and slightly
higher (and surface-based) instability. Some early CAM guidance also
suggests that this feature may be augmented by a remnant MCV, and
most develop more robust convection across a larger footprint of our
area. Still, wind fields and shear remain weak, and the potential
for stronger storms capable of more than just bursts of heavy rain
and occasional lightning appear unlikely. During the day Sunday,
another weak cold front is likely to settle into the area, and we
may see a few redeveloping afternoon showers wherever it
stalls...again most likely in the Ozarks and southwest Illinois.

BRC

&&

.LONG TERM... (Monday through Thursday)
Issued at 352 AM CDT Fri May 22 2026

From Memorial Day through the end of the week, local weather
conditions will be dominated by a quickly-building and highly
amplified upper ridge across the central CONUS, undercut by a weak
subtropical upper low over the latter half of the week. The former
will lead to a gradual increase in temperatures, while the latter
will result in slowly increasing shower/thunderstorm chances Tuesday
onward.

For the Memorial Day holiday, the primary point of forecast
contention appears to be whether showers will continue to linger or
redevelop across parts of the area, as a stalled front and locally
higher moisture will likely persist across our southeast. The
current model footprint of precipitation probabilities is relatively
limited, with roughly 20 to 40% chances (once again) mainly along
and south of I-44. For the rest of the area, dry conditions are most
likely with near or slightly above average temperatures. However,
with such weakly forced and subtle forcing mechanisms at work, the
predictability of precipitation coverage and timing is relatively
low, and we will need to keep an eye on the potential for a more
rapid northward return of Gulf moisture.

And on that note, the latter is expected to be driven by a
meandering subtropical upper low that will undercut the upper ridge
from the southwest. As this occurs, Gulf moisture will steadily
drift northward throughout the week, and likely become maximized in
our area over the area late in the work week. Ensemble mean 850mb
PWAT percentiles during this period climb to near the 90th
percentile, and precipitation chances climb into the 40-70% range
with a strong preference for the afternoon periods. Again, weak wind
fields and the strong diurnal PoP fluctuations suggest that this
activity will most likely be dominated by pulse-type showers and
storms, although there are many mesoscale features that may
influence this that we cannot resolve at this time range.

As for temperatures, the NBM continues to produce a clear shoulder-
season warm bias throughout the ensemble envelope, and the
operational NBM remains the warmest deterministic model for a large
portion of the extended forecast. While the result is not quite as
significant as the last iteration of this bias, where near-record
surface temperatures were being forecast, it is nonetheless
significant enough to make a collaborated manual adjustment to lower
temperatures slightly from the NBM. This may need to be re-evaluated
over time, though, as the model may begin to "catch up" after a few
more days are captured by the bias correction. On the other hand,
the increasing potential for showers and thunderstorms (and cloud
cover) also may limit the ceiling on our temperatures.

BRC

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 614 AM CDT Fri May 22 2026

IR satellite and surface obs show MVFR cloud cover attempting to
fill in out of the southwest this morning. Where MVFR isn`t
already in place, it becomes increasingly favored through the
morning. Showers are expected to develop late this morning into
this afternoon with the low potential for a few thunderstorms.
The potential for direct impacts from thunderstorms is low and
therefore was not mentioned in the TAF at this time and can be
addressed in later amendments if impacts become certain. MVFR
visibilities will accompany more efficient rainfall, along with
ceilings that intermittently dip to IFR.

Rainfall potential pulls east of all terminals this evening.
However light/calm winds and low level moisture could lead to fog
development with MVFR visibilities tonight into early Saturday.

Maples

&&

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

$$

WFO LSX