Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

254
FXUS63 KLSX 190749
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
249 AM CDT Wed Aug 19 2026

.KEY MESSAGES...

- Widespread showers and thunderstorms will continue at least through
  the morning hours, mainly along/south of I-70/I-64 in
  Missouri and Illinois respectively. Locally heavy rainfall is
  possible.

- Additional showers and thunderstorms are expected this
  afternoon and evening. The best chances (40-60%) are in two
  areas: 1) northeast Missouri west-central Illinois and 2)
  southeast Missouri and southwest Illinois. A few storms may be
  strong to severe with damaging winds the main threat.

- Near to slightly below average temperatures are expected to
  continue into the weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 247 AM CDT Wed Aug 19 2026

Widespread showers and thunderstorms are ongoing from eastern
Kansas east/southeast toward the Mississippi River. The
strongest cores (and highest instantaneous rainfall rates) have
been on the southern edge, with more stratiform rain and
embedded thunderstorms to the north/northeast. This is what is
largely impacting our region, though a small portion of central
Missouri as well as southeast Missouri will be under some risk
for flash flooding mainly through the morning hours. Locally
heavy rainfall is possible in these areas where 2-3+" of rain
may occur in a narrow WNW-ESE swath. Gusty winds are also
possible, though radar imagery has shown convection to be mainly
outflow dominant, which makes it more difficult for severe wind
gusts to make it down to the surface.

The low-level jet gradually veers more westerly and does weaken,
though some moisture convergence lingers along/south of I-70 toward
midday. Therefore, I would expect some lingering showers to
percolate at least until that point, if not a bit longer. Where
exactly the effective front will be is still an unknown, but best
guess is near the Missouri-Arkansas border. That would mean
afternoon development of scattered showers and thunderstorms may be
to the south of our southeastern Missouri counties, but it will be
close. Therefore, there is a conditional severe threat down that
way, mainly during the early evening hours. The convective mode may
be mixed, with supercells and line segments possible. Damaging winds
is the primary threat, but any supercell would have a low chance of
marginally severe hail and/or a brief, weak tornado due to the
enhanced low-level shear/helicity near the boundary.

Another area of potential concern is across northeast Missouri and
west-central Illinois this afternoon. Some CAMs have a cluster of
right-moving supercells that move southeast with time through the
morning and into the afternoon. The exact track of this activity
(assuming it does occur) as well as the environment in our area is
not certain. However, if there is some partial clearing and that
area is able to destabilize, those supercells could continue into
that area. Large hail would be the main threat in that area with any
supercells, with damaging wind gusts possible with any mergers. To
further complicate matters, some CAMs (such as the 6Z HRRR) suggest
an MCV may track east/northeast across northeast Missouri/west
central Illinois this afternoon. IF this feature is real, it could
also foster renewed convective development, though the timing may
favor central/northern Illinois more. Convective initiation may also
be aided to its south/southeast, which could mean a few cells
develop in southeast Missouri/southwest Illinois by early evening.
Given the very complex nature of the forecast over the next 12-18
hours, there is very low confidence in how things will evolve.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 247 AM CDT Wed Aug 19 2026

(Thursday - Friday)

Dry weather with near to below normal temperatures are still
expected to end the work week as a weak surface anticyclone moves
into the mid-Mississippi Valley.


(Friday Night - Tuesday)

There remains some subtle, but notable, differences with the large
scale pattern across the CONUS this weekend into early next week.
The EPS remains deeper and farther to the west with the midlevel
trough across the Great Lakes. This sends a cooler air mass far
enough west into our region, and keeps us largely dry. The GEFS is
weaker with the trough and a bit to the east. That means our area
barely gets brushed with the cooler air mass, and sets up a
potential MCS Sunday night into Monday morning as the "ring of fire"
sets up more to the east and more into the mid-Mississippi Valley
compared to the central Plains.

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1034 PM CDT Tue Aug 18 2026

Thunderstorms over western Missouri will move east and affect
COU/JEF between 06-10Z and the St. Louis area terminals between
08-12Z. There is a lower chance at UIN between 08-12Z, so have
kept just a PROB30 group there. Additional thunderstorms will be
possible during the period with the best chance at UIN between
20-24Z. The heavier showers and thunderstorms will have the
potential to produce MVFR/IFR ceilings and visibilities in heavy
rainfall and wind gusts over 30 knots. There will also be some
high MVFR or low VFR ceilings move south into UIN and the St.
Louis area terminals between 12-18Z. Winds will remain mainly
light outside of thunderstorms.

&&

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

&&

$$

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Britt