Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

146
FXUS63 KLSX 231714
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1214 PM CDT Thu Apr 23 2026

.KEY MESSAGES...

- High temperatures in the low to mid 80s are expected today, with
  breezy southerly winds occasionally gusting to 25-35 mph. Most
  rain holds off until tonight, but a stray afternoon
  shower/thunderstorm in northeast Missouri is possible (20-30%
  chance).

- Confidence remains high (80-90%) that the more widespread
  rainfall arrives late this evening and overnight. Scattered
  thunderstorms are expected, with a limited potential for
  isolated damaging wind gusts and locally heavy rain. Overall
  though, the potential for severe storms is low.

- Another round of showers and thunderstorms remains very likely
  (70-80%) late Sunday through Monday.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 236 AM CDT Thu Apr 23 2026

For the most part, the short term forecast remains largely on track,
with a high probability (80-90%) of widespread showers between late
this evening and early tomorrow morning, due to what is expected to
be a large but decaying thunderstorm complex. If any of these storms
remain severe as they arrive (far from a given), isolated damaging
wind gusts will be the most likely hazard, followed by a lesser
threat of a brief QLCS tornado or two. Another very conditional
threat of scattered showers and a few thunderstorms exists tomorrow
afternoon roughly along and south of the I-44 corridor, although
much depends on how tonight`s event evolves.

Driving today`s severe weather threat is a rather complex upper
level flow pattern, featuring the interaction of a cutoff upper low
with both the northern Polar jet stream and a southern subtropical
jet streak. As of this morning, the Pacific low was in the process
of merging with the northern jet, and this is driving robust
cyclogenesis across the far northern plains. The end result of
this will be a large and strong surface low pressure system (which
may already be close to mature and starting to occlude) that will
draw rapid southerly return flow across the central Plains and
Mississippi River valley, and will be followed by a slowly
advancing cold front spanning almost the entire length of the
Plains. At the same time, a secondary low pressure system is
forecast to develop along the tail end of this front in the
southern Plains, which is the surface response to the subtropical
jet streak mentioned previously. Put more succinctly, there will
be a lot going on in the upper levels today.

As the afternoon progresses, southerly surface winds will noticeably
increase, with persistent sustained speeds of 10-20 mph and gusts of
25 to 35 mph. This will draw increasing moisture northward ahead of
the advancing front, but initially the bulk of this moisture
advection will occur well to our west, where substantial instability
will develop across eastern Kansas and western Missouri. As the
front encounters this very unstable airmass (and also a dryline
across the southern/central plains), widespread thunderstorms will
develop, including very likely some severe thunderstorms. The main
implication for us here is that the vast majority of these initial
storms will develop well to our west, congeal into a large
convective complex, and move into our area late in the evening or
overnight. A few high resolution models do suggest that a few open
warm sector storms will be possible farther east during the
afternoon, mainly across northeast Missouri, and if that occurs we
can`t rule out some strong wind gusts or even a couple of marginally
severe hailstones. However, the lack of forcing and a moderate
capping inversion suggest that these areas are favored to remain dry
until the main line of storms arrives later in the evening.

As this complex of thunderstorms arrives in northeast/central
Missouri sometime late this evening (likely between 10pm and 1 am),
surface instability will wane, and storms are expected to gradually
weaken. This is especially true of the northern portion of the
complex (very roughly north of I-70), as the southern portion of the
line will be more favorably oriented with the southwesterly low
level jet and have better access to uninterrupted inflow, not to
mention a more unstable environment in general. This appears to be
reflected in a shift of higher precipitation totals further to our
southwest in HREF guidance, with 75th-90th percentile rain amounts
now only reaching 0.75 - 1.5 inches across parts of the Ozarks, and
progressively lower amounts farther north. It seems that guidance is
really latching onto a weaker line across most of our area, and to
the point where some of our northeasternmost areas may only see
mostly light rain and a few rumbles of thunder.

Given the trends above, it would seem that our potential for both
severe storms and heavy rain have incrementally decreased. Regarding
the severe weather threat, there remains a limited potential for
damaging wind gusts across mainly central and northeast Missouri as
this line of storms initially arrives, perhaps just before it loses
strength. Marginal low level wind shear (~30kt 0-3km) that is
largely parallel to the advancing line, and a significant reduction
of surface-based instability both reduce the QLCS tornado potential
as well, but doesn`t completely eliminate it within more favorably
oriented and more persistent bowing segments.

As for heavy rain, bulk parameters still suggest that 90-95th
percentile precipitable water and line-parallel mean flow will be
present, keeping the door slightly ajar for locally heavy rain.
However, much will depend on if this line can hold together through
our area before it becomes cold-pool dominant, which would cause it
to weaken and rain rates to diminish, and also add a more east-
west motion within bowing segments and limit training over the
same areas. As such, the flooding threat is very limited, and
likely restricted to our southwesternmost periphery
(central/southeast MO).

Latest trends suggest that most of this rain will exit the area to
the southeast by mid-day tomorrow, but there are still indications
that the surface front will stall somewhere near or just south of
the I-44 corridor. This keeps the door open for another round of
scattered showers and a few thunderstorms to redevelop in the
afternoon, although this largely depends on how well we can
destabilize in the wake of the morning rain and cold pools. In the
worst-case scenario, just enough destabilization could lead to 1000-
1500 J/kg of SB CAPE by mid afternoon, with 30-40kt of 0-6km of bulk
shear, with sounding profiles marginally supportive of few stronger
convective cores. However, it is more likely that the worked-over
environment will struggle to produce storms of any real
significance.

BRC

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 236 AM CDT Thu Apr 23 2026

By Friday night, any lingering showers and thunderstorms will exit
the area to the southeast, and a much drier airmass will settle into
the area behind the departing cold front. This is expected to
yield a dry and downright pleasant day Saturday, with slightly
above average temperatures, low humidity, light winds, and no rain
to speak of.

By Sunday, attention turns to the next approaching system, which
ensembles continue to depict with increasing agreement. While the
large upper low that is driving tonight`s event will stall across
the Northern Plains and southern Canada, a stronger southern-stream
shortwave and jet streak will undercut this low and drive another
surface low through the Central Plains and Mississippi River Valley.
Ahead of this low, confidence is growing that another round of
widespread showers and thunderstorms will move through our area
between Sunday evening and Monday morning, perhaps with redeveloping
thunderstorms along an advancing cold front Monday afternoon. NBM
precipitation probabilities during this window have climbed to
between 70 and 80 percent during this time range, with relatively
good agreement in the depiction of the larger synoptic-scale
features among LREF clusters.

There remains some uncertainty regarding the onset of the initial
round of showers and storms (which would likely be elevated), and
also once again the degree of destabilization that can be achieved
Monday afternoon after the morning activity. However, regarding the
latter, this system may be better able to overcome the stabilizing
effect of morning rain due to the presence of a stronger low
pressure system and persistent southerly return flow, depending on
how quickly the cold front moves east. These details will not be
resolved for another few days, but there is at least a reasonable
"worst-case" scenario that could result in another round of strong
or severe thunderstorms Monday afternoon/evening.

BRC

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1205 PM CDT Thu Apr 23 2026

Dry and VFR conditions are forecast through mid evening. Then a
line of showers and scattered thunderstorms is expected to move in
from the west, first affecting UIN/COU/JEF between 03-06Z with
predominant showers and a PROB30 group for thunderstorms between
05-08Z. These same conditions will affect the St. Louis area
terminals with showers between 09-15Z and a PROB30 group for
thunderstorms between 09-12Z. Any of the heavier showers or
thunderstorms could produce IFR ceilings and visibilities and wind
gusts of 35 knots or greater. MVFR ceilings between 1500-3000 feet
are expected to move into the area on Friday morning (around 15Z)
before improving to VFR on Friday afternoon.

Britt

&&

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

$$

WFO LSX