Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

045
FXUS63 KLSX 201931
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
231 PM CDT Wed May 20 2026

.KEY MESSAGES...

- Cooler temperatures will continue through Friday before readings warm
  up closer to normal levels for the Memorial Day holiday
  weekend.

- There are chances of showers (and maybe a few thunderstorms)
  daily Friday onward, with the highest chances (70-90%) on
  Friday.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 229 PM CDT Wed May 20 2026

The strong (1026+ hPa; ~99th percentile of climatology) surface
anticyclone across the Upper Midwest continues to control our
weather across the mid-Mississippi Valley. Light northeast/east
flow will continue to bring in cooler and drier air into the
region at least through Thursday. Cloud trends are the main focus
in the short term, as they will heavily influence temperatures -
both day and night. Clouds tonight are expected to be most
prevalent across the southern half of the area with at least a
partially clear sky across northeast Missouri and west-central
Illinois. Lows will be warmer where it stays cloudy (mid 50s) a
majority of the night, and coolest (mid to upper 40s) where more
clearing is expected. Gradually increasing mid/high level clouds
are forecast on Thursday, helping to keep highs near the 70 degree
mark, or 5-10 degrees below normal for the date.


Gosselin

&&

.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 229 PM CDT Wed May 20 2026

(Thursday Night - Friday)

The strong surface high pressure loses influence quickly Thursday
night as a midlevel shortwave trough moves out of the south-central
Plains into southeast Missouri. This feature induces surface
cyclogenesis along the stalled front across the mid south. This low
then moves northeast through Friday into eastern Illinois.
Widespread rain showers are expected on Friday, though there is some
temporal variation on exactly when the best rain chances will
reside. Taking a blend of the faster GFS and slower ECMWF would
focus on the late Friday morning/afternoon hours. The highest rain
amounts should be across east central and southeast Missouri as well
as southwest/south central Illinois where large scale forcing for
ascent should be strongest. Total amounts main exceed 0.50" in spots
as LREF probabilities do climb above 50% in these areas. While many
areas have been quite wet this spring, parts of southeast Missouri
could certainly use the rain. Temperatures on Friday will be tricky,
and will of course will depend on timing. However, if the thicker
clouds and rain arrive early enough in the day and stay long enough
than temperatures will really struggle to climb much above 60
degrees. The trifecta of low clouds, persistent rain, and northeast
surface winds is a recipe for very low diurnal ranges. In these
scenarios where those three conditions last most of the day,
temperatures tend to only rise a few degrees - even in the warm
season. This would put some areas potentially not reaching the 60
degree mark as mentioned above.


(Friday Night - Next Wednesday)

Surface moisture will continue to gradually increase heading into
the holiday weekend. Multiple weak midlevel shortwaves are forecast
to move through the broader region, but both the timing and track of
each of these features is uncertain at this time range. The general
theme looks to shift more toward diurnal shower/weak thunderstorm
chances especially Sunday into Memorial Day itself (and beyond).
Unlike Friday, any rain for the holiday weekend does not look too
widespread nor long lasting. Plenty of dry time should exist each
day, but rain chances may tend to peak during the afternoon/early
evening hours when daytime instability is maximized.

Temperatures are forecast to gradually warm up through the holiday
weekend, though largely should stay at or slightly below normal with
highs mainly in the 70s and lows in the mid 50s to low 60s through
the Memorial Day holiday. Mean temperatures on both the GEFS/EPS do
climb above +15C by the middle of next week though, which may
portend to slightly above normal daytime highs. The deterministic
NBM and its percentiles continue to have a distinct warm bias due to
60-day bias correction and high temperatures were lowered each day
after collaboration with the WPC.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1220 PM CDT Wed May 20 2026

Ceilings will slowly rise today, with bases generally 3-5 kft AGL.
Winds will veer from the north to the east/northeast through the
period.

Gosselin

&&

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

$$

WFO LSX