Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

566
FXUS63 KLSX 041126
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
526 AM CST Wed Mar 4 2026

.KEY MESSAGES...

- Showers and thunderstorms will persist at times through Thursday
  morning. The most numerous thunderstorms are expected late this
  morning into afternoon with a few severe thunderstorms possible
  between 12 and 5 pm today in southeastern MO/southwestern IL.

- There will be additional rounds of showers and thunderstorms
  Thursday night and Friday night/Saturday morning. There is a
  conditional threat of severe thunderstorms again Friday evening
  into overnight.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 331 AM CST Wed Mar 4 2026

Showers and thunderstorms, with the strongest thunderstorms possibly
producing small hail, have become more isolated to scattered in
coverage early this morning with a veering LLJ focusing associated
forcing more toward the east of the CWA. Coverage should remain
limited until late this morning through afternoon, when a loosely
organized MCS in phase with an upper-level shortwave trough, tracks
east/northeastward through the CWA. CAMs indicate that these
thunderstorms will be a mixed mode with a few transient supercells
also possible and predominantly elevated with a marginally severe
hail threat. The main severe threat, however, will be tied to the
location of a front wavering across southeastern MO and southwestern
IL where the probabilities of 1000+ J/kg SBCAPE have been slightly
increasing in recent HREF runs, now at 30 to 50 percent along/south
of the front. If sufficient surface-based instability is available
to thunderstorms, damaging winds and an isolated tornado are also
hazards, especially with enhanced surface vorticity near the front.
The severe threat will mainly be from 12 to 5 pm today.

The MCS will likely force the front and instability to the south of
the CWA this evening, resulting in another lull in showers and
thunderstorms at least locally. Showers and thunderstorms will
increase in coverage again tonight and attempt to lift back
northward into the CWA as the LLJ restrengthens. There is increasing
confidence that ingredients will be present for heavy rainfall
including PW near the 99th climatological percentile, deep layer
flow aligned with the slow-moving front/composite outflow, and the
strength of the LLJ reaching 40 to 50 kt. The latest HREF QPF LPMM
also has a corridor of 2 to 4" extending northeastward into
southeastern MO and southwestern IL, but there are some CAMs that
keep trailing showers and thunderstorms persisting near the MO-AR
border through the evening, preventing instability from pushing back
northward and the threat of heavy rainfall from extending into the
CWA. With the consideration that soils are still dry and have a
large capacity of absorption in addition to the dependency on
convective evolution, it appears there is a conditional threat of
heavy rainfall but it is even more unclear whether or not there would
be flash flooding.

At a minimum, there will be showers at times tonight that linger
into Thursday morning, especially along/south of I-44 (MO) and I-55
(IL). The front is expected to stall near southeastern
MO/southwestern IL through much of the day, but pronounced mid-level
height rises in the wake of the shortwave trough will be unfavorable
for much additional showers and thunderstorms until the front starts
to lift back northward Thursday evening/night with a LLJ developing.
With less precipitation and even breaks in clouds, high temperatures
are forecast to be warmer across the CWA and in the 60s and 70s F.

Pfahler

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 331 AM CST Wed Mar 4 2026

On Friday morning, the warm front may still be lifting northward
across northeastern MO/west-central IL, accompanied by some showers
and thunderstorms, but most of the daylight hours on Friday is
anticipated to be dry with probabilities of measurable rainfall at a
relative minimum thanks to a lack of forcing and a capping
inversion. Friday will be the warmest day of the week as the CWA is
fully in the open warm sector with 850-hPa temperatures around the
99th climatological percentile, and even some downslope warming off
the Ozark Plateau with a southwesterly component to low-level flow.
NBM probabilities of 80+ F high temperatures are 40 to 70 percent
along/south of the Missouri River, but exact values will be
dependent on how much cloud cover is present and how deeply mixed
the boundary layer becomes.

Conditions will be favorable for severe thunderstorms to develop
across KS and western MO Friday afternoon and evening along and
ahead of an eastward advancing cold front, and subsequently track
eastward into the CWA sometime Friday evening into overnight. There
is some variability in the timing of the cold front, arriving in
northeastern and central MO anytime between 03 and 06z Friday
evening, with earlier timing obviously leading to a higher severe
threat with probabilities of 500+ J/kg quickly falling through the
night from between 20 to 50 percent to below 10 percent after 06z.
It is worth noting that these probabilities are also relying on
global models properly resolving the boundary layer`s stability,
which can result in them under-forecasting instability. Considering
the potential both QLCS and supercell convective modes, a
conditional threat for damaging winds, large hail, and tornadoes is
apparent Friday night, highest in the western half of the CWA.

Showers and thunderstorms may still be exiting the CWA in
southeastern MO and southwestern IL during the morning on Saturday,
but dry conditions will prevail otherwise this weekend into Monday.
A cooler post-frontal airmass will arrive on Saturday but the exact
potency of this airmass is not completely certain with NBM
interquartile high temperature ranges around 10 F, generally in the
50s and 60s F though. Thereafter, a warming trend will prevail with
favorable low-level southwesterly flow and WAA returning
temperatures to well-above average, 70s to near 80s F on Monday.

The next opportunity for showers and thunderstorms will come
sometime late Monday through mid-next week, but this opportunity
will be largely driven by the ejection of an upper-level cutoff low
from the Desert Southwest through the Mid-Mississippi River Valley.
Global models often have a difficult time resolving cutoff low
ejections and there is quite a bit of uncertainty on the timing of
this process, with timing differences on when ensemble model
membership has measurable rainfall, ranging from Monday night to
late Wednesday.

Pfahler

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 526 AM CST Wed Mar 4 2026

Showers and thunderstorms are largely crossing into IL this morning
and departing the terminals, but IFR flight conditions are expected
at all terminals due to eventual expansion of stratus through the
morning and areas of fog. A cluster of showers and thunderstorms
will track through the area late this morning through afternoon,
near and south of the I-70 corridor. These showers/thunders are
actually anticipated to improve flight conditions to VFR or MVFR in
their wake, but a relapse will take place this evening with
southward expansion of IFR stratus. Additional showers and some
thunderstorms will move into parts of the area tonight, but it is
uncertain when and if thunderstorms will directly impact any of the
terminals. Areas of fog will also be a source of visibility
reductions outside of precipitation.

Pfahler

&&

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

$$

WFO LSX