Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

689
FXUS63 KLSX 211912
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
212 PM CDT Fri Aug 21 2026

.KEY MESSAGES...

- Seasonably cool late summer temperatures are expected this
  weekend into next week with few opportunities for rain.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 210 PM CDT Fri Aug 21 2026

Currently a ridge of high pressure over the Intermountain West
has spread hot and dry conditions out into the Plains. A trough
centered over Hudson Bay has extended its influence southward
into the Great Lakes, with this trough expected to continue
pushing into the Great Lakes and New England over the coming
days. A leading shortwave trough is pushing through Wisconsin
toward Chicago this afternoon, with a cold front sliding
southward behind it. There are two primary areas of convection
expected in the next 12 to 24 hours along this front:

The first is closer to the shortwave trough tracking into
northern Illinois. Here some modest moisture convergence aided
by lift from the shortwave trough will lead to scattered
thunderstorms potentially merging into a broader complex pushing
southeast overnight. It is likely that these storms track to
the east of our forecast area, but there`s an outside chance (20
percent) that they do move through our far eastern counties
overnight. While there is some severe weather threat with this,
the threat will be greatest in the evening hours closer to the
core of the thunderstorm complex. The threat locally will be
considerably lower and later in the night.

The second is to the west over Nebraska and Kansas. Here a low
level jet this evening will send modest moisture northward
toward the front and trigger another thunderstorm complex to
develop. This tracks southeast potentially into western Missouri
overnight, but is unlikely (less than 10 percent) to make it
into our forecast area.

The most likely scenario for us tonight will be a subtle passage
of the cold front overnight, with winds turning out of the north
by morning. Expect a mostly sunny day behind the front on
Saturday. Despite cold advection, deep post-frontal mixing will
ensure it`s another warm day in the mid to perhaps upper 80s.
That deep mixing, though, is expected to mix in some drier air
from aloft. We`ve deliberately included more of the higher
resolution guidance in the forecast to reflect this drying. Some
guidance has dewpoints falling well into the 50s with a
corresponding increase in temperature.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 210 PM CDT Fri Aug 21 2026

As we go through the weekend, the trough spins into
southeastern Canada while the ridge expands its influence
eastward into the Rockies and Great Plains. Surface high
pressure moving in behind tonight`s front will ensure that our
area remains more under the influence of the cooler air mass
from the trough despite rising heights aloft. Highs only reach
the low 80s with lows in the low 60s or even upper 50s at times.

As the ridge nudges eastward our area will become better
situated to have some effects from ridge running shortwave
troughs, what we sometimes call the "ring of fire" of
thunderstorm complexes rotating around a ridge. At first, low
level moisture is pretty limited due to northerly low level flow
near the Gulf, but over the next few days better moisture does
eventually lift northward into the Southern Plains. It has more
difficulty moving eastward, though, as the influence of the
surface high moving into the western Great Lakes and Ohio Valley
remains strong. We`ve seen a growing consensus in guidance at
this point for the focus of convection Sunday into Monday to
stay just to our southwest along with the effective warm front.
Some cloud cover from this activity to our west may actually
help to hold temperatures down even further on Monday,
potentially in the 70s. Meanwhile on the other side of the warm
front the heat is on with temperatures potentially near 100.

The next more substantial shortwave trough tracks through the
northwest flow on Wednesday, but it`s not clear we ever get into
the warm, moist air by then. So despite the passage of another
weak cold front, we may not get any rain out of it. NBM POP
remains low (less than 20 percent), and most of the low
resolution ensemble guidance keeps the focus for precipitation
to our south where the better moisture exists or to our north
where the core of the upper wave will be. Additional shortwave
troughs have some potential (20 percent or less) to bring
additional rounds of showers and storms through the end of the
week, but confidence gets lower with time on when and where
those waves will track. There is a general consensus, though,
that the ridge eventually expands far enough east that we
eventually get in on the warmer weather again. NBM probability
of 90 degree heat increases to about 30 percent by Friday.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1219 PM CDT Fri Aug 21 2026

For the most part, VFR conditions and light winds are expected
over the coming 24-36 hours. There is a weak cold front moving
through overnight, but it`s unlikely to produce any
thunderstorms locally and will most likely move through dry.
There could be some valley fog by morning, though confidence is
not very high on this. This would be most likely at SUS.
Otherwise winds become NNW by Saturday morning with VFR
expected.

&&

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

&&

$$

SHORT TERM...Kimble
LONG TERM...Kimble
AVIATION...Kimble