Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

752
FXUS63 KLSX 091044
AFDLSX

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

.KEY MESSAGES...

- Near record high temperatures are possible today and Tuesday.

- Showers and thunderstorms are expected late Tuesday into
  Wednesday morning. Some of the storms may be severe, mainly
  during the late afternoon and evening. Locally heavy rainfall is
  also possible through Tuesday night.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 343 AM CDT Mon Mar 9 2026

Persistent southwest flow along with strong early-March sunshine and
deep mixing will push temperatures well above normal today. Forecast
soundings show mixing up to 850mb and above this afternoon with
temperatures around 14-15C.  The latest deterministic NBM highs in
the mid to upper 70s are a few degrees cooler than the what the
850mb mix-down temps would indicate. I think this is likely too cool
due to bias correction.  Therefore I am leaning toward the 75th
percentile for highs today which pushes much of Missouri along and
south of I-70 into the 80-82 range with the remainder of the area in
the mid to upper 70s which is near to above record highs..  There is
still a bit of uncertainty to throw into the equation: low level
moisture will also be increasing, and a few guidance members show
isolated showers developing in the afternoon due to some weak
moisture convergence.  However, forecast soundings show a pretty
substantial inversion above 850mb, so convection looks very unlikely
at this time.  Warm/moist advection on southerly flow continues
tonight tonight which will keep overnight lows well above normal in
the mid 50s to around 60.


Carney

&&

.LONG TERM...  (Tuesday through Sunday)
Issued at 343 AM CDT Mon Mar 9 2026

Tuesday looks even warmer than today due to the mild start to the
morning and continuing low level warm advection.  Forecast
soundings mix up to between 900-850mb across most of the region,
higher in northeast Missouri and west central Illinois.  850mb temps
around 16C would mix down to around 84F At the surface which the
latest NBM is showing across much of central and east central
Missouri, with lower 80s elsewhere.  Think it could get warmer,
though the limiting factor will be increasing clouds as low level
moisture continues to build.  Regardless, highs will be near records
again on Tuesday.

Attention turns to severe potential late Tuesday afternoon and
evening.  Most discrete guidance is showing MLCAPE values building
in excess of 2500 J/Kg across parts of central and eastern Missouri
into west central/southwest Illinois by late Tuesday afternoon. Some
models (most notably the RAP) are showing MUCAPE values in excess of
3500 J/Kg between 21Z Tuesday 00Z Wednesday, generally across
northeast Missouri into west central Illinois.  Kinematics are
favorable for rotating updrafts given the strong instability with 0-
6km shear between 40-50kts.  However, forecast soundings show a
significant capping inversion Tuesday afternoon across the area, and
some doubt remains whether thunderstorms can develop during the late
afternoon/early evening when instability will be highest.  The most
likely location for CI Tuesday afternoon will be across northeast
Missouri into west central Illinois in the vicinity of a quasi-
stationary front where low level forcing will be strongest and the
cap will be weakest.  Discrete supercells will be possible which
would present all hazards including hail in excess of 2 inches,
damaging winds and a few tornadoes.

The window for severe storms should close quickly as most guidance
shows instability dropping to less than 1500 J/Kg by mid-late
evening.  Locally heavy rain then becomes a potential issue late in
the evening and overnight as low pressure drifts across northern
Missouri along the front.  GFS/RAP show a broad 40-50kt low level
jet producing at least moderately strong moisture convergence over
Missouri and Illinois as it encounters the low level baroclinic
zone.  Forecast soundings show a relatively deep warm cloud depth
(especially for this time of year) of nearly 10,000ft, and NAEFS/ENS
P-wats are in the 99th climatological percentile.  Therefore expect
continuing thunderstorms Tuesday night to be efficient rain
producers as they move across the area.  Locally heavy
rainfall/flooding is possible, mainly across northeast Missouri into
west central Illinois if thunderstorms train over the same
locations.  The front should start moving before 12Z Wednesday as a
short wave trough moves from the Plains into the Midwest.  This
forces low level cyclogenesis along the boundary, and the resulting
low pushes the front through Missouri and Illinois on Wednesday.

The remainder of the forecast looks relatively quiet. The NBM is
forecasting near to above normal temperatures through the period,
though there is considerable uncertainty for Friday through Sunday.
Thursday will likely be the coolest day through the forecast period
with near normal temperatures as high pressure moves across the Mid
Mississippi Valley.  The GFS and ECMWF show a clipper moving across
the Upper Midwest Friday which drags a dry cold front across
Missouri and Illinois. The front is forecast to stall Friday night
and then lift back to the north Saturday. Another stronger trough
moves into the Central U.S. Sunday which pushes the front back
through the Mid Mississippi Valley with a chance for precip. The
LREF is showing considerable variance in temperatures through this
period as it appears its members are showing a great deal of
difference in the position of the front. High temperature IQRs
increase from around 10 degrees Friday to 20+ degrees by Sunday.
Confidence in the temperature forecasts is therefore low in the
Friday-Sunday time frame.


Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 536 AM CDT Mon Mar 9 2026

An area of IFR ceilings/visibilities will affect parts of the
eastern Ozarks and southern Illinois this morning. The low
ceilings are expected to lift and scatter by 16-18Z. Additionally,
low level wind shear conditions will persist for a few hours this
morning across central and northeast Missouri and west central
Illinois. Otherwise, VFR flight conditions are expected to
prevail today and into this evening. Low ceilings are likely to
redevelop late tonight across parts of northeast Missouri and west
central Illinois as a front drifts into the region. Low ceilings
are also possible across the eastern Ozarks again late tonight.

Carney

&&

.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