Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

514
FXUS63 KLSX 122326
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
626 PM CDT Sun Apr 12 2026

.KEY MESSAGES...

- Showers are expected this afternoon and evening, with the best
  chance (60-80%) for rain across central/northeast Missouri and
  west- central Illinois.

- Several chances for showers and thunderstorms will impact the
  region this week, with the greatest chance for storms Tuesday
  evening/night and again Wednesday afternoon/night. Some storms
  could be severe both Tuesday and Wednesday.

- Above average temperatures are forecast to last until at least
  Friday.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 152 PM CDT Sun Apr 12 2026

Recent GOES-East water vapor imagery reveals an amplified longwave
trough near the West Coast with broad ridging across the eastern
U.S. producing southwesterly flow across the region. Currently, a
mid-level shortwave is lifting northeastward within the
southwesterly regime from the Plains into the Midwest. This, coupled
with a strong low-level jet (40-60kts), leading to increased low-
level moisture convergence, is sustaining a broad area of showers
that has lifted northeast out of OK/KS and is now approaching
central Missouri early this afternoon. High-res guidance resolves
this field of precipitation continuing northeast, with the greatest
coverage of showers forecast across central/northeast MO and west-
central IL. This is where the latest HREF has the swath of greatest
rainfall with the LPMM accumulated precipitation indicating a swath
of 0.1-0.2" with isolated pockets up to 0.50", which is possible for
locations where heavier showers move over. Some locations across
southeast MO/southwest IL may remain dry as the coverage of showers
across that area is forecast to be more scattered. The reason being
that the greatest mid-level forcing and core of the low-level jet
later this afternoon and evening is progged by guidance to move
across northern MO eastward into northern IL. An isolated pop-up
thunderstorm cannot be ruled out this afternoon/early evening as
HREF mean SBCAPE values reach 250 J/kg before crashing to zero after
sunset. On the heels of the departing mid-level shortwave and
greater forcing for ascent, model guidance unveils a subtle ridge
nudging in from the west, resulting in weak height rises aloft
beginning later tonight. As a result, showers are forecast to exit
from west-east later this evening, with a low chance (20-30%) for
scattered lingering showers across southern IL overnight.
Temperatures this afternoon are in the 70s across most the area (60s
where showers are falling) and will remain warm in the 60s overnight
as continued low-level WAA and cloud cover prevail.

Instability begins increasing from west-east around midnight, with
mean HREF SBCAPE values over 500 J/kg across Missouri by sunrise on
Monday. This is the result of increasing surface moisture along with
the passing mid-level shortwave veering winds aloft leading to
steepening lapse rates, generally above 700mb. By Monday afternoon,
mean HREF SBCAPE ranges from 1,500-2,500 J/kg, with the greater
values across central/northeast MO and west-central IL. Even with
ample instability in place, and modest 0-6km Bulk Wind Shear near
30kts, thunderstorms are not expected due to the influence of the
ridge aloft. However, it is important to note that some
deterministic guidance resolves weak nebulous areas of forcing
within the subtle mid-level ridge. Therefore, a scattered shower or
an isolated thunderstorm Monday morning into Tuesday is still
possible, but that chance is low (10-20%). With another day of
strong southerly flow and at least some solar insolation in between
breaks in cloud cover, Monday will be very warm with highs forecast
in the 80s for the entire area.

Peine/BRC

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 152 PM CDT Sun Apr 12 2026

At the start of the extended, the mid/upper-level longwave trough
will be near the Four Corners Region with continued broad ridging
across the eastern U.S. keeping the area within a southwesterly
regime. With continued southerly flow leading to increased low-level
moisture, instability will trend upwards into Tuesday with LREF mean
SBCAPE values up to 2,500 J/kg across central/northeast MO by
Tuesday afternoon. As the longwave trough slowly pushes eastward,
nearing the High Plains by Tuesday afternoon/evening, chances for
showers and thunderstorms return as LREF chances for QPF >0.01"
steadily increase from Tuesday evening into Wednesday morning. The
12Z RRFS A resolves convection forming across northeastern OK
Tuesday afternoon and pushing northeast, rapidly weakening as it
approaches our area. Analysis of forecast soundings indicates a 750-
900mb warm nose associated with strong WAA in that layer that would
lead to a capping inversion resulting in elevated thunderstorms. The
warm nose progged by guidance appears to be weaker to the north and
west, meaning that the greatest severe threat appears to be across
central/northeast MO and west-central IL, as thunderstorms may
weaken with eastward extent. As of now, with a setup like the one
described above, the greatest hazards for Tuesday afternoon into
Wednesday morning appear to be large hail and damaging winds.

An additional threat for severe weather exists Wednesday afternoon
into early on Thursday, when the longwave trough is forecast to
eject into the Plains and Midwest. This is when the most robust mid-
level forcing for ascent and greatest 0-6km bulk wind shear (40-
50kts) will be collocated near the area. Instability looks less
impressive Wednesday into Thursday, as mid-level lapse rates weaken,
resulting in widespread LREF mean SBCAPE values of 500-1,000 J/kg on
Wednesday. However, the previously mentioned 750-900mb capping
inversion may erode Wednesday afternoon/evening, allowing for
potential surface based convection. Once again, the greatest mid-
level forcing/instability/shear overlap looks to be across
central/northeast MO and west-central IL.

Behind the longwave trough ejection, long-range guidance has good
consensus that shortwave ridging quickly moves into the area
Thursday, shunting chances for showers and thunderstorms east. This
gives the area a brief break from the more active pattern with dry
and warm conditions forecast for Thursday afternoon into Friday
morning. Just upstream, across the West Coast, another longwave
trough will be advancing east nearing the region by Friday
afternoon. Compared to the longwave trough midweek, this longwave
looks to be more progressive and may eject into the Plains by the
end of the week or early next weekend. As a result, chances for
showers and strong to severe thunderstorms return to the area Friday
afternoon into Saturday, along with a chance for cooler temperatures
next weekend. Warmer than average temperatures will continue until
Friday with LREF temperature IQR spreads around only 3-7 degrees
during this period. However, on Saturday, temperature IQR spreads
jump to 20 degrees with spreads down to 10 degrees or less on Sunday
centered on temperatures just below average.

Peine/BRC

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 620 PM CDT Sun Apr 12 2026

Radar mosaics show light showers progressing through the region
from southwest to northeast this evening. No thunder was observed
with little expectation for thunder to develop with limited
instability. Despite the showers, most cigs remain at or above VFR
levels. The exception is a narrow band of MVFR that extends down
the back side of the precipitation. Any eastward shift in the MVFR
deck will be impeded by the mid-level ridge that extends westward
from the southeast CONUS into the mid-Mississppi Valley.
Conditions are largely expected to remain VFR with the highest
potential for MVFR extending from KCOU to KUIN. It`s a close call
for KJEF with much of the lower cigs remaining northwest of the
terminal. Gusts take a brief break late tonight into early Monday,
but return mid-morning Monday. VFR is expected to settle in by
late morning through the remainder of the period.

Maples

&&

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

$$

WFO LSX