Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

213
FXUS63 KLSX 131859
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
159 PM CDT Mon Apr 13 2026

.KEY MESSAGES...

- Severe thunderstorms are possible Tuesday night and again Wednesday
  afternoon into evening. The better chance for severe weather
  exists on Wednesday. Large hail and damaging winds will be the
  primary threats each day.

- A potent cold front will pass through the region late this week, bringing
  another chance for strong to severe thunderstorms and an end to
  the unseasonable warmth.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 157 PM CDT Mon Apr 13 2026

Water vapor imagery shows an upper-mid level longwave trough over
the northwestern third of the CONUS with an upper-low level ridge
dominating the remainder of the country. The Mid-Mississippi
Valley`s weather is being influenced by the northwestern portion of
ridge as seen by strong, deep southwest flow throughout the
atmospheric column. We`re seeing this at the surface in the form of
temperatures in the 80s, which is 20 degrees above normal for mid-
April. Gulf moisture is also being advected in along the
southwesterly flow, as characterized by dewpoints in the 60s.
Needless to say, there is an abundance of warmth and moisture in the
region. This translates to an abundance of instability as well,
which leads us into Tuesday and Wednesday`s severe potential.

The bottom line for Tuesday is that the potential for severe
thunderstorms in our area is low. Despite being located within an
open warm sector and an 80% HREF probability of having 2500+ J/kg of
SBCAPE in place, a strong capping inversion is expected to keep
convective initiation at bay through the afternoon. A lack of any
forcing or mid and upper level lift supports at least mostly dry
weather as well. Instead, supercells are expected to fire off a
dryline in Kansas southward through Texas in the afternoon and
become severe as they drive northeast. By the time they reach
central Missouri in the evening, daytime instability will be quickly
waning and CIN quickly growing. If the mass of thunderstorms is
still severe by the time it arrives, the increasingly unfavorable
environment it moves into will ensure it won`t stay severe for long.
If any thunderstorm does remain severe, large hail and damaging
winds will be the primary threats.

A strengthening low-level jet Tuesday night will keep ongoing
convection from eroding completely and/or spark new initiation. None
of this is expected to be severe, but it may impact the potential
for severe thunderstorms on Wednesday especially if it lasts well
into the morning.

Jaja

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 157 PM CDT Mon Apr 13 2026

By 1pm Wednesday, the longwave trough currently over the western
CONUS will be centered in the High Plains. A jet streak will extend
northeastward through the Southern Plains and into the Great Lakes
region, skimming our CWA along its extent. Though the best upper
level forcing will exist to our northwest, we`ll still be in the
right entrance region of the jet streak and will be able to take
advantage of the more robust upper level support. The same can be
said in the mid-levels where forcing increases ahead of an incoming
shortwave. In the low-levels, a surface cyclone will be pushing
northeast from Nebraska into the Upper Midwest, dragging a cold
front into northwestern Missouri to serve as forcing for ascent.
This will all make for a much better set-up than Tuesday. The only
potentially mitigating factor will be instability. More
specifically, how well the boundary layer will recover after Tuesday
night`s/Wednesday morning`s low-level jet driven convection. The
latest LREF shows only up to 1000 J/kg of SBCAPE in place by 1pm.
This is a much lower value than Tuesday`s 2500+ J/kg, but with so
much support at all levels, it shouldn`t matter. Effective bulk
shear will also be in the 35-45 kt range, which is more than enough
to support severe weather even given the lower instability. Shear
vectors are forecast to be about 45 degrees off of the cold front.
This may result in discrete thunderstorms capable of large hail and
damaging winds initially before congealing into a line or multi-
cell mass. Minor shifts in the bulk shear vectors may change storm
mode drastically. More than 45 degrees and supercells will be
favored. Less than 45 degrees and a QLCS will likely develop
faster with damaging winds being the primary threat.

As mentioned, thunderstorms will weaken in the hours after sunset.
Two mid-level shortwaves, one in the Upper Midwest and another in
the Mid-South, will pass Wednesday night into Thursday, and another
low-level jet will ramp up along and ahead of the cold front. These
features will offer continued support for ascent, and will keep non-
severe convection going until the Mid-South shortwave exits late
Thursday. The cold front is not expected to clear the area entirely,
but will instead buckle northward as a warm front late Thursday. A
lack of cold air behind the front will make its passage and return
basically unnoticeable as highs reach the widespread upper 70s
and low 80s again Thursday. A much more potent cold front will
drive through the region late Friday/early Saturday and will bring
a real rush of cool air into the area. Although there`s still
uncertainty regarding how cool we get, the NBM 75th percentile
high temperature forecast for KSTL on Sunday is only 71 degrees.
There is another chance of thunderstorms on Friday ahead of the
cold front with severe weather possible again. The potential for
severe weather will rely on the timing of the cold front, which at
this point is still very uncertain.

Jaja

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1219 PM CDT Mon Apr 13 2026

Gusty southwest winds will persist through the TAF period for most
locations. Areas outside of central Missouri, northeast Missouri,
and west-central Illinois may see a brief reprieve overnight with
gusts falling below 20 kts. A southwesterly low-level jet will
intensify tonight in our western and northern areas, but the
threat of LLWS will depend on if gusts diminish at all in these
areas. As mentioned previously, gusts are forecast to persist.
However, if this changes then LLWS will be added to the TAFs for
tonight.

Jaja

&&

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

$$

WFO LSX