Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

415
FXUS63 KLSX 092320
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 PM CDT Mon Mar 9 2026

.KEY MESSAGES...

- Near record-high temperatures are possible again on Tuesday.

- There is a threat of severe thunderstorms on Tuesday, mainly in
  the evening across northeastern MO/west-central IL, conditional
  on thunderstorms initiating in the evening versus overnight.

- More widespread showers and thunderstorms are expected
  overnight Tuesday night into early Wednesday afternoon with
  transition toward more of a locally heavy rainfall threat.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 243 PM CDT Mon Mar 9 2026

Low-level southerly flow/WAA and a lack of boundary layer decoupling
will lead to a very mild night tonight with low temperatures in the
upper 50s to low-60s F across the CWA, possibly setting the stage
for breaking daily record maximum low temperatures. These mild
temperatures and 850-hPa temperatures nearing seasonal
climatological maximums will assist Tuesday in being another very
warm day across the area with high temperatures once again reaching
the mid-70s to low-80s F, approaching daily records. However, with
increasing moisture there should also be areas of
stratocumulus/cumulus and some mid-level clouds that will at least
slightly limit insolation and keep the anomalous 850-hPa
temperatures from directly translating to surface temperatures.

The warm and moisture airmass entrenching the CWA in the warm sector
will also help bolster seasonably high instability during the
afternoon (most model guidance agreeing on MLCAPE reaching 1500 to
3000 J/kg) along with deep-layer shear of 35 to 50 kt, providing
favorable conditions for severe thunderstorms. The main point of
uncertainty remains the aforementioned 850-hPa temperatures leading
to a capping inversion, delaying the development of thunderstorms.
The capping inversion is most likely to be overcome across
northeastern MO and west-central IL near a west-to-east
warm/stationary front leading a weak surface low with a subtle
approaching upper-level shortwave trough, but CAMs vary between
initiation as early as 22z and as late as 06z. If thunderstorms can
develop in the CWA earlier in this window when instability is
greater, supercells are at least initially expected, with the main
hazards being very large hail (steep lapse rates and large amounts
of CAPE in the hail growth zone) and tornadoes. With 150 to 200+
m2/s2 of 0-1 km SRH, a strong tornado is possible, primarily along
the front where there is greater low-level hodograph curvature.
Although forcing is weak during the evening, deep-layer shear will
be nearly parallel with the front, suggesting storm mergers and
upscale growth could occur with time, leading to damaging winds
becoming the main hazard. All of this being said, this period of
greater severe threat is somewhat conditional, since some CAMs/short-
term models actually delay thunderstorm initiation beyond this
period of more favorable parameter space, with greater support for
earlier initiation across central/north-central IL.

Coverage of showers and thunderstorms will more confidently increase
Tuesday night as upscale growth occurs along the warm front and
approaching cold front, the LLJ strengthens, and additional showers
and thunderstorms potential enter the CWA from the southern Ozarks.
It is most likely that overnight thunderstorms will be largely
elevated as the boundary layer stabilizes and instability becomes
overturned. That being said, pockets of greater instability and
constructive thunderstorm interactions could provide a lingering
marginal severe threat of isolated damaging winds and marginally
severe hail. Locally heavy rainfall could also become the primary
hazard in a favorable environment with PW exceeding the 99th
climatological percentile and warm cloud depths around 10 kft, but
whether or not flash flood occurs will come down to thunderstorm
evolution with wind profiles at least supportive of training and
backbuilding thunderstorms into the LLJ. The latest HREF QPF LPMM
highlights northeastern MO and west-central IL with 1 to 2.5". Given
that this signal is not particularly strong and there is sensitivity
to thunderstorm evolution, the threat of flash flooding is currently
not high enough to warrant a Flood Watch.

Pfahler

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 243 PM CDT Mon Mar 9 2026

An upper-level trough and cold front will be passing through the CWA
Wednesday morning into early afternoon accompanied by the finale of
showers and thunderstorms. Probabilities of 500+ J/kg SBCAPE are
only 20 to 40 percent in global ensemble guidance, lowering
confidence in any severe thunderstorms by that time, which aligns
with the concern for plentiful prefrontal/warm sector clouds and
lingering overnight precipitation. Precipitation will gradually end
altogether from west to east during late morning through afternoon,
but clouds will linger longer and allow low-level CAA to lead to a
largely non-diurnal temperature trend with temperatures falling into
the 40s and 50s F behind the cold front.

Upper-level northwesterly flow will dominate the Mid-Mississippi
River Valley Thursday through Saturday. An upper-level
trough/Alberta Clipper will traverse this flow sometime early
Friday, which casts uncertainty on high temperatures on Friday and
Saturday regarding the timing of the associated cold front and
potency of the post- frontal airmass. Therefore, NBM interquartile
temperature ranges reach 10 to 15 F, but there is generally an
underlying warming temperature trend from around average on
Thursday. Frontal passage is also forecast to be largely dry with
highest probabilities of measurable rainfall to the north of the
CWA where forcing will be greater. Global model guidance signal a
more potent upper-level trough cross the Mid-Mississippi River
Valley around Sunday into Monday, but there is increasing
variability in its amplitude, timing, and track. These factors
will have implications on the structure and track of the low-level
cyclone and precipitation amounts, although there is a much more
pronounced signal for precipitation than the Alberta Clipper.
Around 20 to 40 percent of ensemble membership has precipitation
changing to/falling as snow across northeastern MO/west-central IL
in colder, more southerly cyclone tracks.

Pfahler

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 610 PM CDT Mon Mar 9 2026

Impacts to several of the local terminals are expected tomorrow.
An approaching weather system will gradually increase low-level
moisture across portions of the region through tonight, with
pockets of low stratus moving into KUIN, KCOU, and KJEF around
sunrise. While these conditions will be surrounding KSUS, KSTL,
and KCPS, confidence is low in direct impacts at these three
terminals. Daytime heating is expected to lift this stratus
through the late morning and early afternoon, with at least a
brief period of VFR flight conditions expected during the
afternoon at all local terminals.

Just beyond the end of the current TAF period, a cold front will
slowly sag southward into the region, with widespread thunderstorm
activity expected along it. These thunderstorms will impact KUIN
with at least heavy rainfall and low visibilities. Impacts prior
to 00z can`t be ruled out at this lead time, but given the low
confidence and lead time, they were left out of this TAF issuance.

Elmore

&&

.CLIMATE...
Issued at 211 PM CST Sat Mar 7 2026

Daily record high temperatures may be threatened both on Monday 3/9
and Tuesday 3/10. Below are the records for each day from our
official climate sites:

            Monday 3/9          Tuesday 3/10
KSTL        80F (1925)          86F (1955)
KCOU        80F (1986)          82F (1955)
KUIN        75F (1986)          79F (1955)


Gosselin


&&

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

$$

WFO LSX