Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

556
FXUS63 KLSX 011146
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
646 AM CDT Wed Apr 1 2026

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms are forecast
  through Saturday. There is the potential for severe
  thunderstorms Thursday and Friday nights, but these chances are
  highly conditional.

- A cold front will pass this weekend, ushering in dry weather and cooler
  temperatures.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 355 AM CDT Wed Apr 1 2026

A quasi-stationary boundary, as of 06z, stretches from about
Versailles, MO northeastward through Nokomis, IL and beyond. With
the help of a modest low-level jet, showers and weak, elevated
thunderstorms have become widespread along and north of the front.
So far this morning, the most robust thunderstorms in our area have
been able to produce small hail at most. More notable is rainfall
portions of the area has gotten so far. According to MRMS, a stripe
of 1" to 3" of rain has already fallen in central MO and in south-
central IL along the front, and there is more rain to come. Despite
this, flash flooding is still not considered a major threat due to
dry antecedent conditions, progressive storm motion, and lack of
backbuilding or appreciable training. With that being the case, if
training does become a problem, the aforementioned areas may
experience nuisance flooding.

The coverage of tonight`s showers and thunderstorms will begin to
decrease in the morning as the low-level jet weakens. However,
convection is expected to ramp back up again along the front by this
afternoon as daytime instability increases and mid-level vorticity
lobes pass through the region. Exact coverage is somewhat uncertain,
as model guidance is disagreement regarding how strong the mid-level
support will actually be. Generally it seems fairly weak, which
paired with capped low-levels and long, skinny CAPE makes the chance
of seeing severe weather low. If any thunderstorms do become strong,
small hail will be the primary hazard. Thunderstorms are expected to
be largely relegated to the front and south, which is still forecast
to land near the I-70 corridor unless currently developing cold
pools push the boundary farther south. The placement of the front
will also drastically impact the temperature forecast, creating a
tight gradient between highs in the 50s to the north of the front
and highs in the 70s and 80s to the south.

A mid-level trough will dig into the Plains today, spurring the
intensification of surface cyclogenesis in western Kansas/eastern
Colorado. Along the system`s dryline in western Oklahoma and Texas,
convection is expected to fire up in the late afternoon. This
convection will congeal as it moves northeast into Missouri during
the evening hours as a low-level jet concurrently strengthens over
northeast Oklahoma/southwest Missouri. This brings us to tonight`s
very low severe weather threat. The concern is that the
thunderstorms from the Southern Plains may hold up if not be
intensified from the low-level jet as far east as our CWA. However,
instability will be very low by the time they arrive, and limited at
most to a sliver of the mid-levels outside of the hail growth zone.

More importantly will be the aforementioned surface cyclone dragging
our quasi-stationary north as a warm front by Thursday morning. This
will place us within the open warm sector, with strong southerly
winds advecting warm and moisture into the Mid-Mississippi Valley.
In a perfect scenario, surface based instability will be able to
accumulate ahead of the system`s weak cold front, and a mid-level
trough will be present to provide lift. The only mitigating factors
to convective initiation on Thursday are 1) the question of
atmospheric recovery behind tonight`s round of thunderstorms and 2)
timing. Many of the CAMs are pessimistic, showing little to no
robust convection, and even the few optimistic ones initiate
thunderstorms so late in the evening that they die quickly. If they
are wrong, however, and we get earlier and more robust CI, 1000-2000
J/kg of SBCAPE paired with 30-40 kts of bulk shear oriented
fairly orthogonally to the front would support at least semi-
discrete convection to start, with unidirectional shear suggesting
splitting supercells with all hazards possible.

Jaja

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 355 AM CDT Wed Apr 1 2026

Though we transition into the long term discussion, the potential
for severe weather is not over yet. Thursday`s weak cold front will
not pass through the CWA, but rather buckle northward as a warm
front as a second surface cyclone traverses the Plains. This will
leave us within the warm sector again for Friday. There is still
uncertainty regarding how much, if any, pre-frontal convection we
get during the afternoon. Mid-level forcing and a cap could preclude
thunderstorm development, or at least preclude any meaningful
thunderstorms. The NAM is the only model sounding without a cap, and
even in this possible worst case scenario lift is very poor within
the hail growth zone and hodographs over time are straight, again
supporting splits. The best chance for severe weather will likely be
along the cold front Friday night. The biggest mitigating factor
here is the timing of the frontal passage. If the front is earlier
in the evening, more instability will likely be present and our
threat for severe weather will increase. If it passes later,
instability will have had time to diminish, and our severe threat
will decrease. In the earlier scenario, increasingly northward
pointing bulk shear vectors would promote abundant cell interaction,
and damaging winds and QLCS tornadoes would be the primary threats.
The severe threat would also include a larger portion of the area
than if it arrives later.

The cold front will pass Friday night into Saturday, ushering in
cooler and drier weather. Although the drier weather is forecast to
stay a while, temperatures are forecast to rebound quickly as has
been the pattern it seems.

Jaja

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 556 AM CDT Wed Apr 1 2026

Showers and thunderstorms will continue on and off throughout the
TAF period. This morning`s convection will diminish in the mid to
late morning with the weakening of the low-level jet. However,
coverage will increase again this afternoon in the vicinity of a
stationary front that is expected to set up near or south of I-70.
Coverage will increase further tonight as thunderstorms arrive
from the Southern Plains and the low-level jet ramps up again.
MAY need to add LLWS areawide in the next issuance to reflect the
low-level jet depending on how strong surface winds remain
overnight. The stationary front will also split the wind forecast,
with easterly winds to the north of the boundary and largely south
winds to the south of the boundary.

Ceilings are forecast to remain IFR to very low MVFR north of the
boundary through the TAF period. Largely VFR conditions will
prevail to the south, but with the boundary expected to be
wavering near I-70 this makes forecasting ceilings a challenge for
the Mid-Missouri and St. Louis metro terminals. As of now, keeping
the forecast pessimistic.


Jaja

&&

.CLIMATE...
Issued at 238 AM CDT Sun Mar 29 2026

Records at Regional Long-Term Climate Sites - March 31st

             Record Highs | Record Warm Lows

St. Louis:   87F (1981)   | 63F (1917)
Columbia:    86F (1940)   | 59F (1967)
Quincy:      81F (2010)   | 58F (2010)


&&

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

$$

WFO LSX