Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

772
FXUS63 KLSX 300330
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1030 PM CDT Wed Jul 29 2026

.KEY MESSAGES...

- Temperatures will be near to slightly below normal today and
  Thursday. It will also be less humid than in recent days.

- Showers and a few thunderstorms are likely Thursday night
  through Friday night. A chance for rain lingers Saturday.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 107 PM CDT Wed Jul 29 2026

Today: Surface high pressure is currently centered over
Wisconsin and is slowly moving to the southeast. Across
central/ eastern Missouri and western Illinois winds are out of
the northeast with only some very shallow cumulus and thin high
clouds across central Missouri. The surface high pressure will
slowly move southeast through the day today and tonight as the
longwave trough axis moves east. Dewpoints have also responded
to the dry air slowly advecting in from the east this afternoon
and are now in the lower to mid 60s. Temperatures are expected
to top out in the mid to upper 80s today.

Tonight through Thursday night: Surface high pressure will
center over Illinois Thursday morning with surface winds veering
from the southwest. By Thursday afternoon into evening, a piece
of vorticity at 500 mb will advect east across the Dakotas. As
this happens, the longwave trough axis will begin to buckle and
elongate. Precipitation will start to move in late Thursday
night, but given the broken off low over New England and the
impending wave breaking at 250 mb the thinking is that most of
Thursday night will be dry.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 107 PM CDT Wed Jul 29 2026

By Friday, the aforementioned vorticity will begin to sweep
southeast across Iowa with showers likely and a few
thunderstorms. At 500 mb, the wave axis will be seasonably
strong with heights falling to around 582 dam or ~ 2 SD
anomalies below normal for this time of year. Simultaneously, at
250 mb a jet streak is forecast to round the base of the
shortwave trough giving a slight enhancement to the upper level
divergence. Regarding instability, the GFS continues to
advertise MU cape values approaching 3800 J/kg Friday afternoon.
Taking a look at the LREF though, MU CAPE values are advertised
to be much more reasonable around 1600 J/kg. Surface to 6 km
shear is forecast to be around 35 kt. Given the above, SPC has
outlooked the region (mainly central Missouri) in a marginal
risk. Damaging wind gusts appear to be the primary threat
(mostly in the afternoon and early evening hours of Friday).

Saturday and beyond is where model guidance starts to diverge.
In particular, the deterministic GFS and ECMWF continue to
oscillate back and forth on whether a closed low, or wave
breaking, will occur from the Friday vorticity. Why does this
matter? If a closed low forms, precipitation chances will likely
hold on longer (into Sunday and possibly Monday). If a closed
low doesn`t form (or is really weak and forms east of
Missouri), the area will likely dry out sooner. Analyzing the
latest WPC cluster analysis reveals that the GEFS and GEPS
ensemble suites are most similar and advertise a more
progressive solution (not a closed low forming). In fact, the
EPS which has broad support for a closed low appears under
dispersive. 50% of the EPS guidance is clustered together with
only 15% of the GEPS and 3% of the GEFS. This under dispersion
of the EPS has allowed us to continue to trend our thinking
towards Sunday being more of a dry forecast with below normal
temperatures. For the beginning of the next work week, near
normal temperatures and mostly dry conditions will persist.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1006 PM CDT Wed Jul 29 2026

High pressure dominates the sensible weather across the Mid-
Mississippi Valley and Ohio Valley tonight through tomorrow,
resulting in dry and VFR conditions. Rain chances increase from
west to east after 06Z Friday along an unusually strong upper-
level trough for late July, which may result in flight
restrictions developing across parts of the region. The best
chances for this exist from central Missouri through west-
central Illinois, including KCOU, KJEF, and KUIN. The St. Louis
metropolitan terminals have a lower chance of these
restrictions, but the chances are not zero that far south.

&&

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

&&

$$

SHORT TERM...BAH
LONG TERM...BAH
AVIATION...MRB