Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

901
FXUS63 KLSX 230752
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
252 AM CDT Sat May 23 2026

.KEY MESSAGES...

- Showers and a few thunderstorms will move through the area this
  evening and overnight. While rain will be mostly light and
  storms not strong or severe, highly localized pockets of 1-2
  inches of rain are possible (20% chance).

- Near to slightly above average temperatures and mostly dry
  conditions are expected Memorial Day, with a chance (20-40%) of
  showers/weak thunderstorms along/south of I-44 in the afternoon.

- Near to slightly above average temperatures are expected Tuesday
  through the end of the work week, with increasing chances
  (50-80%) for repeating afternoon pop-up showers/thunderstorms.

&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 226 AM CDT Sat May 23 2026

Warmer conditions can be expected this afternoon thanks to
briefly clearing skies, building heights, and modest southwesterly
flow. However, a round of scattered showers and a few
thunderstorms is expected to slowly move through the area this
afternoon and through the night. While occasional lightning and
bursts of heavy rain can be expected with stronger cores, severe
storms are not anticipated.

The synoptic-scale pattern will continue to feature a slow moving
upper trough across the northern plains and upper Mississippi River
valley, which will draw southern stream impulses northeastward and
into our area. One such impulse is expected to move across Missouri
between late this afternoon through the overnight hours, which may
be augmented by an MCV emanating from convection currently ongoing
in north-central Texas and Oklahoma. As this feature moves into
Missouri later this afternoon, it is expected to encounter a
modestly unstable airmass (500-1000 J/kg SBCAPE) thanks to
improved insolation and warmer surface temperatures from yesterday
(upper 70s- low 80s), although condensed in a relatively shallow
layer thanks to mid/upper level subsidence. Ambient wind fields
are also expected to be weak, with only about 25-30kt of effective
shear to work with (unless the MCV can provide its own local
enhancement). Even in the more bullish scenarios, the parameter
space generally supports pulse- type convection or possibly a few
clusters, and strong/severe storms are not expected. As for rain
amounts, while it may take some time to saturate a mid-level dry
layer, eventually this is expected to occur and PWATS will reach
1.5-1.7" (90th percentile), and this will support at least briefly
heavy rain rates. Total rain amounts will be highly variable,
with a few pockets of locally heavier rain (1- 2") embedded within
a broader area of light rain (.25" or less).

Model guidance consistently depicts that the core of this activity
will slowly move northeast roughly along the I-44/70 corridor
through the evening and overnight, and exit to the east near
sunrise. Behind it, a weak cold front will sink into the area and
settle just south of the area, ushering in a drier airmass. While a
few redeveloping showers may clip parts of the Ozarks and southwest
Illinois in the afternoon, most areas are expected to remain dry
Sunday with near average temperatures.

BRC

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 226 AM CDT Sat May 23 2026

Very little change to sensible weather can be expected Memorial Day,
as an elongated surface ridge will remain overhead and a stalled
surface front draped across our southeastern periphery. Temperatures
will once again reach near seasonal averages, with a few
redeveloping afternoon showers and weak thunderstorms possible (20-
40%) roughly along and south of the I-44/70 corridor. Again, this
activity is not expected to be strong or severe, but may pose an
occasional lightning threat to outdoor events.

By Tuesday, an abrupt change in the synopitic-scale pattern will
result in a rapidly building and highly amplified upper ridge across
the U.S. and Canadian Plains. This will be a semi-permanant feature
for several days thereafter, closely resembling an Omega Block
pattern with meandering closed lows on either side. Meanwhile, a
weak, east/west oriented upper trough is expected to undercut this
ridge, and remain draped across the lower Mississippi River Valley
and Gulf Coast from Tuesday through the end of the work week. Within
this broader trough, multiple subtropical impulses are likely to
provide local foci for showers and storms at various points
throughout the week.

This is expected to impact our local weather in two primary ways.
First, an extended period of near to slightly above average
temperatures is expected from Tuesday through the end of the week.
While final highs are likely to depend heavily on precipitation
trends, confidence is high in the overall trend thanks to very
consistent ensemble guidance and relatively narrow spreads. Once
again, the NBM continues to display a shoulder-season warm bias
throughout its members, and our official forecast is a slightly
reduced version of this guidance. Second, repeated episodes of
primarily diurnal showers and thunderstorms are also increasingly
likely from Tuesday through the end of the work week. While
mesoscale details are unresolved, the large scale pattern will
favor weak upper level flow and wind shear, which limits our
ceiling for strong/severe storms and generally favors pulse-type
convection and clusters. However, long range ensemble mean PWAT
forecasts continue to suggest values near and above the 90th
percentile from mid to late week, which would support repeated
episodes of afternoon showers with variable but locally heavy
rain.

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 944 PM CDT Fri May 22 2026

MVFR flight conditions are expected to prevail across most of the
area for the rest of the night, with IFR ceilings continuing to
hang on across the eastern Ozarks. A few sprinkles or light rain
showers will continue to diminish through 05-07Z and are not
expected to affect ceilings or visibilities before dissipating
entirely. Guidance continues to show areas of fog developing
across parts of central Missouri after 09Z if ceilings clear out.
If this happens, visibilities could drop to 1 mile or less in
spots, particularly in sheltered/low lying areas. Any fog that
develops should lift and scatter within an hour or two of sunrise
Saturday morning. Remaining MVFR ceilings are expected to lift and
scatter by 17-19Z. Several models are developing showers and
thunderstorms over southwest/central Missouri during the late
afternoon, and moving them slowly east through the evening. Timing
and coverage of the thunderstorms is inconsistent between guidance
members, however feel confidence is high enough to include prob30s
at the central Missouri and St. Louis Metro terminals.

Carney

&&

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

$$

WFO LSX