Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

444
FXUS63 KLSX 201748
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1248 PM CDT Mon Apr 20 2026

.KEY MESSAGES...

- Above normal temperatures are expected Tuesday through Thursday
  with widespread 70s to low-80s.

- Widespread showers and thunderstorms arrive late Thursday night,
  and continue into early Friday. There is the potential for
  redevelopment Friday afternoon into Friday evening.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 215 AM CDT Mon Apr 20 2026

Surface high pressure was centered over eastern Iowa with another
surface high over southwest Arkansas. The northern high has pushed a
weak cold front into the area with mid to high clouds stretching
from north-central Missouri through the metro area into southern
Illinois. As of 07z, surface temperatures ranged from the upper 40s
to low-50s with dewpoints largely in the low to mid-30s. Easterly
surface winds remain at 5-10 knots with few locations showing
lower wind speeds.

Clouds aren`t quite thick nor widespread enough to have a broad
impact on temperatures. Most locations are expected to fall into the
low-40s with mid to upper 30s in the cooler locations of northeast
Missouri and west-central Illinois. While patchy frost is possible
in the cooler areas, it`s a similar theme to yesterday morning. The
air remains too dry, the presence of light wind, and now some cloud
cover to account for. With the surface ridge departed to the north,
winds are not expected to calm. Considering the lack of frost
yesterday morning, there`s a stronger argument against it than for
it.

After a cool start, we`ll see temperatures rebound with a subtle,
but noticeable warming trend from the southwest. 850mb temperatures
rise to near 10C west of the Mississippi River with west-southwest
flow rounding the Gulf ridge. Temperatures will largely be
similar to Sunday`s with exception to central and southeast
Missouri. Ridging begins to build west to east from the Plains
with warmth having greater influence just north and east of the
Ozark Plateau, where temperatures warm into the low to mid-70s.


Maples

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 215 AM CDT Mon Apr 20 2026

As surface high pressure moves west to east across the Upper Midwest
and into the Great Lakes late Tuesday, it pushes a weak cold front
southward into the mid-Mississippi Valley Tuesday night. RAP/NAM
deterministic solutions show the surface boundary stalling near or
north of the MO/IA border with a narrow corridor dewpoints in the
low-60s pooling along and south of the boundary.

Further south (LSX CWA) of this west-east oriented axis of moisture,
air dries rather quickly with dewpoints in the 40s/50s. Mid-level
fields show a squeeze play occurring between the boundary and height
rises at the northern end of the Gulf ridge. This lines up west to
east from northern Missouri into west-central Illinois. West-
southwest surface to mid-level flow persists, likely working against
the southward progress of the boundary. WAA process already take
over at the west end of the front in eastern Kansas and western
Missouri. F-gen remains concentrated to the northeast of the CWA
with weak convergence riding under a muted upper shortwave.
Precipitation that attempts to develop will fall into a deep dry
layer that extends from the surface to 800mb. <20% of the LREF
members depict measurable precipitation skimming the northeast
border of the CWA. Dry conditions are favored with isolated showers
at best.

WAA strengthens Wednesday through Thursday as the axis to a mid-
level ridge moves overhead from west to east. The warmest air
remains over the central Plains, where H8 temperatures are in the
mid to upper teens (C). This air is gradually pulled eastward
through the 48 hour period, but moderated to the low teens (C) as it
approaches the Mississippi River. This is likely to be the warmest
stretch of the week with widespread 70s to low-80s.

Long range guidance is coming into better agreement with the late
week system. A cutoff, closed upper low traverses the Pacific
Northwest and consolidated with a digging trough over Canada. This
deepens the surface low over the northern Plains as a cold front
extends south of the surface low through the eastern Plains. Strong,
southerly pressure gradient flow extends north/south over eastern
Kansas, where MUCAPE values approach or slightly exceed 2000 J/kg in
the vicinity of a 50-60 kt LLJ. Initial thunderstorm development is
favored across the eastern Kansas/northwest Missouri late Thursday.
From that point onward, spread begins to increase as result of
specifics with convective trends. 35-40 knots of 0-6km shear will
support organized multi-cell development that eventually congeals
into QLCS line that moves eastward overnight into Friday morning.
The ECMWF shows a south-southeast track over southwest Missouri that
likely plays off the CAPE gradient over the southwest corner of the
state. This doesn`t make as much sense when steering flow is out of
the southwest. The more likely scenario is a blend between the
northern track of the GFS that takes most of the activity through
central and northern Missouri.

This disagreement leads to QPF disparity that, in reality, is likely
larger than the LREF spreads. They show 0.25"-0.75" between the
inner quartile range. Considering PWATS of 1.4-1.5 inches cover the
region, convective trends will tap into copious moisture with
amounts that will easily exceed IQR within thunderstorms.
Thunderstorms will outrace the better CAPE to the west with
weakening convection moving into central Missouri around midnight
Thursday night. Widespread showers and embedded thunderstorms
progress eastward through Friday morning. Much of the area receives
another soaking rainfall with ECM/GFS ensemble members loosely
clustered around an inch through Friday morning. Several members
rise above an inch with the uncertainty in where the complex tracks.
This introduces another challenges heading into Friday with
additional chances for showers and thunderstorms.

As the upper trough performs a Fujiwara dance with multiple vort
lobes over the northern Plains, the front bends more west-east with
time. This typically signals a slowing southward progression and
ultimately has the boundary bisecting the CWA from northeast to
southwest Friday afternoon. Over 90% of the ensemble members show
overcast skies holding through Friday afternoon, which limited
surface instability. That being said mid-level lapse rates of around
8C line the front over somewhat more modest CAPE values (~1500 J/kg)
around 18z Friday. Long range guidance has some development along
the boundary with 0-6km shear around 35 knots. Friday will be a day
to watch, especially if trends begin to break cloud cover and allow
better recovery of surface instability. If so, strong to severe
thunderstorms cannot be ruled. This holds true for either round, but
will have better support Friday if typical diurnal trends can be
realized.

The front slide south Saturday as high pressure clears things out.
Yet another surface low ejects out of Colorado into the southern
Plain late Saturday, but rain chances likely arrive just after the
end of the long range period.


Maples

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1247 PM CDT Mon Apr 20 2026

VFR conditions will prevail for the entire TAF package. Light
easterly/southeasterly winds will gradually become increasingly
southerly with gusty southwesterly winds on Tuesday.

Peine

&&

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

$$

WFO LSX