Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

522
FXUS63 KLSX 221747
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1247 PM CDT Wed Apr 22 2026

.KEY MESSAGES...

- Temperatures of 5-15 degrees above average continue today and
  tomorrow, with breezy south winds tomorrow afternoon.

- Confidence remains high (80-90%) in widespread rainfall Thursday
  night through Friday with a chance (30-50%) of thunderstorms.
  While a few storms may pose a threat of damaging wind, the
  chance for severe storms is higher to our west and southwest.

- Chances continue to increase (50-70%) for another round of
  showers and thunderstorms Sunday night through Monday.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 330 AM CDT Wed Apr 22 2026

While the return of active weather is just around the corner, today
will feature little more than above average temperatures, with
increasing southerly winds tomorrow in addition to the continued
warmth.

After yesterday featured gusty southwesterly winds throughout the
day, a weakening pressure gradient today should keep winds to a much
more reasonable 10 to 15 mph, with occasional gusts in the 20-25 mph
range. Meanwhile, very similar temperatures can be expected, as a
weak cold front straddling our northern periphery is expected to
dissipate prior to the afternoon, and an upper level ridge will move
directly overhead. While we lose a bit of warm air advection due to
the weakening winds, the combination of the ridge and (mostly) full
sun should lead to another afternoon near 80 degrees and no
precipitation. The "mostly" caveat applies to a layer of low clouds
that is currently moving through western Missouri and expected to
move into parts of central/northeast Missouri and west-central
Illinois by early this morning. These clouds are being driven by low-
level moisture advection and weak isentropic ascent, and may linger
through morning or even into the early afternoon before dissipating.
In areas where clouds linger, afternoon temperatures will be a few
degrees cooler than yesterday.

By tomorrow, the first hint at our upcoming pattern change will
arrive in the form of increasing southerly winds, which will develop
in response to a large low pressure system across the Northern
Plains (which I will go into more detail about in the long-term
discussion to follow). While this southerly return flow will result
in slowly increasing humidity and instability, the bulk of the
shower/thunderstorm activity is expected to remain to our west
through daylight hours, while we see little more than gusty winds
(15-20 mph sustained, gusts to 25-35) and a slight increase in
temperatures. This will change later in the evening and overnight,
and for more on that, keep reading below.

BRC

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 330 AM CDT Wed Apr 22 2026

Driving the transition to a more active pattern will be a rather
complex evolution of both the polar and subtropical jet streams
as they interact with a meandering cutoff Pacific low pressure
system in between them. The aforementioned Pacific low is now
mostly onshore and occupying a large portion of the intermountain
west, and over the next two days will slowly phase with the
northern stream jet and both expand and deepen. This will drive
cyclogenesis across the northern plains, and produce a large and
strong surface low pressure system (which was alluded to in the
short term discussion). Meanwhile, a southern-stream subtropical
jet streak will interact with the southern periphery of this
expanding low, and drive the development of a secondary surface
low across the southern plains.

These dynamics will produce showers and thunderstorms across a large
portion of the central Plains and Mississippi Valley Thursday and
Friday, including in our local area. However, the initial activity
will develop well to our west across portions of eastern Kansas and
western Missouri during the day Thursday, where substantial
instability will meet a slowly advancing cold front. Where this
occurs at peak heating, widespread thunderstorms are expected to
develop and eventually grow upscale into one or more thunderstorm
lines, along with at least a few severe thunderstorms. Then, these
storms will slowly move southeast with the cold front, and
eventually through our area between late Thursday evening and Friday
morning. The crux of this forecast is, for the most part, two-fold.
First, how strong will these storms be as they move through our area
overnight when instability wanes, and how long will they last into
the day Friday?

For our portion of the event, the thing we are most confident about
is that most areas will see soaking rain, although with variable
amounts and a limited flooding threat overall. From an environmental
standpoint, a narrow corridor of relatively rich moisture will
develop ahead of the cold front, with PWAT values of around 1.2-1.4
inches, or roughly the 90-95th percentile of climatology. The cold
front and the advancing line of showers/storms will have a large
parallel component to the mean flow, and likewise will advance
relatively slowly overall. Meanwhile, there will also be at least
some convective elements with locally heavy rain rates.

On the other hand, some other factors may also limit the ceiling of
our rainfall, as storms may be weakening as they arrive, and most
parameters are only marginally supportive of truly heavy rain in our
area. Most model guidance suggests that the focus of the most robust
storms will be just to our southwest and perhaps extending into the
Ozarks where instability is forecast to be highest and stronger
storms may be more long-lived. Here, 75th-90th percentile rain
amounts climb up to around 1.5-2.5 inches, which appears
reasonable where convective elements are more persistent. Further
northeast these amounts gradually taper, and this reflects the
lower instability present in these areas. All of this suggests
that if there is a threat of flash flooding it would likely be
limited to parts of central MO and the Ozarks where the
environment best supports the potential for more prolonged and
heavier rain, and where substantial recent rain has fallen. Even
then, this threat appears greatest just to our southwest.

Meanwhile, the threat of strong to severe storms will exist to some
degree, but appears to be limited by the overnight timing. Most
model projections indicate that storms will not arrive in
central/northeast MO until after dark, and maybe not even until
close to midnight. With the loss of surface-based instability and
only marginal wind shear (25-35kt 0-6km bulk shear) and forcing
aloft, not to mention linear storm modes, it`s difficult to envision
much more than the threat of a few isolated strong/severe wind gusts
within the first couple hours of when storms arrive, before this
transitions into mainly a rain event.

By Friday afternoon, the main item of contention continues to be the
timing of the cold front, and whether or not it will linger in our
area into the afternoon before exiting. There remains considerable
model spread regarding this potential, and even if the front does
hang around (thanks largely to the secondary surface low in the
Southern Plains), much will depend on if we can destabilize in the
wake of widespread morning rain. For now, we will maintain a chance
of thunderstorms through Friday evening across mainly the Ozarks and
southwest Illinois.

Beyond Friday, ensembles appear to be putting some separation
between the first rain event and the next one, with largely dry
conditions now expected Saturday and most of Sunday. Sometime Sunday
night and Monday, a stronger southern-stream shortwave and jet
streak is likely to move through the area, driving another round of
showers and thunderstorms at some point in this window. Details on
this event remain sparse, but it is more clear now based on
converging ensemble clusters that we are looking at two distinct
rounds of showers and thunderstorms with a roughly 48 hour break in
between, rather than just prolonged rain chances between Thursday
night and Monday.

BRC

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1247 PM CDT Wed Apr 22 2026

A broad area of low MVFR stratus across much of Missouri has been
affecting KCOU/KJEF/KUIN this morning, as a result of low-level
southerly moisture advection. Northeastward advection of this
stratus field has halted over the last hour as substantial erosion
continues along the northern/eastern edges with the help of abundant
solar insolation outside the stratus. Conditions at KCOU/KJEF will
be the slowest to improve with gradual improvement/scattering
forecast later this afternoon. KUIN is now on the northeastern edge
of this deck and is expected to scatter out in the next few hours.
Confidence is increasing that the St. Louis metro terminals will
stay VFR as the MVFR stratus continues to erode just off to the
west. Otherwise, light southwesterly winds become more southerly
overnight with gusty winds returning after sunrise on Thursday.

Peine

&&

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

$$

WFO LSX