Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

757
FXUS63 KLSX 022312
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
612 PM CDT Sat May 2 2026

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms are forecast for
  the area Monday night into Wednesday.

- Chances for strong to severe thunderstorms along with heavy
  rainfall remain low.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 141 PM CDT Sat May 2 2026

Analysis of the most recent GOES-19 mid-level water vapor imagery
reveals ridging across the Intermountain West, with troughing across
the eastern United States, placing us under northwesterly flow.
Within the northwesterly flow aloft, a subtle shortwave is also
unveiled that is swinging across the area today. The more robust
forcing for ascent associated with the passing shortwave is located
across Illinois and points further to the east-southeast. This is
also where better low-level moisture is located, which has led to
MUCAPE values of 100-300 J/kg, aiding in scattered showers
percolating southeastward across Illinois throughout the day.
Satellite imagery reveals the most agitated cumulus is located just
to the southeast of the St. Louis metro, which is also where
occasional lightning and isolated instances of pea size hail have
occurred over the last hour. This stronger activity is forecast to
continue pushing southeast away from the St. Louis metro area this
afternoon and evening.

Behind the weak cold front earlier this morning, low-level northerly
flow bringing continued CAA has kept the area rather cool today with
most locations topping out in the upper 50s to lower 60s this
afternoon. A weak surface high, currently to the northwest, is
sliding southward toward the region with the center progged to move
over later this evening. As the high continues to slide south across
the area tonight, southerly flow commences from north to south.
Therefore, the onset of return flow will be much slower to the
south, with onset potentially holding off until sunrise for
locations generally south of I-70 in MO and IL. With a prolonged
span for efficient radiational cooling, low-lying/river valleys
across this region are forecast to reach the mid/upper 30s,
potentially leading to areas of patchy frost. For the remainder of
the area, north of I-70, lows are forecast to be in the lower 40s.

After a chilly start to Sunday, increasing low-level southerly
return flow will lead to a quick warmup, with most locations
forecast to be in the low/mid 70s by Sunday afternoon. Southerly low-
level flow will continue to ramp up thanks to a tightening surface
pressure gradient as a weak cold front sinks southward across the
Midwest towards the area. This cold front slowly makes it way into
the area late on Sunday, with some high-resolution guidance keying
in on the front stalling and washing out across the area Sunday
night into Monday, which would lead to weaker surface convergence.
At the same time, within the northwesterly flow aloft, another
shortwave will close in on the area Sunday evening/night, bringing
forcing for ascent along with steepening mid-level lapse rates in
its wake. Forecast model soundings Sunday afternoon and evening
indicate a capping inversion around 800mb, with 500-1,000 J/kg of
MUCAPE above the inversion by the late evening. Instability in the
mid-level may increase slightly after sunrise thanks to the
steepening lapse rates mentioned above. However, even with this
thermodynamic modification, instability is progged to remain below
1,000 J/kg. Most CAMs initiate showers and thunderstorms along and
south of I-70 shortly after sunset with progression to the southeast
overnight. As a result, thunderstorms are forecast to remain weak
with low potential for an isolated stronger thunderstorm leading to
small hail, followed by a lesser threat for damaging winds Sunday
night.

Peine

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 141 PM CDT Sat May 2 2026

Showers and thunderstorms from Sunday night are expected to be
exiting to the southeast by Monday morning as the mid-level
shortwave shifts eastward as well. From Monday into Wednesday, the
large-scale pattern will feature broadened troughing to the north
across Southern Canada with a robust closed low near the Baja Coast.
Another cold front, tied to a surface low across southern Ontario,
will be sliding southward across the Midwest on Monday, leading to
increased low-level southerly flow across the area resulting in
continued warm/moist advection. With the area in the warm sector the
entire day Monday, temperatures will reach the mid 70s to low 80s
across the area. A marginal threat for severe weather exists on
Monday, particularly Monday evening/night as this front closes in
on the area. LREF mean SBCAPE is largely over 1,000 J/kg Monday
evening with instability quickly diminishing after sunset to values
less than 500 J/kg Monday night. As of right now, the cold front is
progged to be moving through overnight as instability is waning,
which would limit the overall severe weather threat.

With the abundance of variance regarding the timing of this front
and its southward progression through the area, it results in lower
confidence for the forecast Monday night into Tuesday. In general,
as this front approaches the area, chances for showers and
thunderstorms increase, with the LREF and NBM both indicating 70-90%
chances for measurable precipitation Monday night into Tuesday
night. Several areas of nebulous mid-level energy will propagate
eastward within zonal flow aloft, interacting with the surface
boundary, resulting in what may be multiple rounds for showers and
thunderstorms Monday night into Tuesday night.

By Wednesday, the broad longwave trough north of the area swings
southward and merges with the eastward propagating closed low across
the Intermountain West, leading to a shortwave ejection into the
Midwest on Wednesday. This larger scale feature shunts the nearby
cold front through the area, taking precipitation chances with it,
and leading to much cooler conditions with highs expected to be in
the 50s for the entire area on Wednesday. In fact, the 75th
percentile for high temperatures on Wednesday is about 20 degrees
lower than the 25th percentile on Monday, indicating a rather large
cool down between Monday and Wednesday. Guidance varies greatly
after Wednesday with several important large scale features, with
the general consensus on the return of northwesterly flow aloft.
Analysis of temperature IQR`s shows a gradual warming trend may
begin late next week, although spreads of 10 degrees or more
indicate a lack of agreement.

Peine

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 611 PM CDT Sat May 2 2026

Light winds overnight become SSW by morning. VFR conditions
continue tomorrow, but some late evening showers and thunderstorms
are expected to develop mainly after 00Z Monday.

Kimble

&&

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

$$

WFO LSX