Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

147
FXUS63 KLSX 041120
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 AM CDT Sat Apr 4 2026

.KEY MESSAGES...

- Showers and thunderstorms will come to an end from west to east
  this morning.

- Much cooler temperatures will arrive through the day today,
  remaining in place into early next week with a 30 to 60 percent
  chance of a freeze Tuesday morning in northeastern MO/west-
  central IL.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 302 AM CDT Sat Apr 4 2026

A weak QLCS continues eastward across the CWA early this morning,
reaching southeastern, east-central MO and south-central IL. So far,
this QLCS has been slightly outflow dominant in the presence of
modest MLCAPE of 250 to 750 J/kg, which has precluded its ability to
produce damaging winds and tornadoes despite 0-3 km wind shear of
around 30 kt supporting mesovortex generation with northeastward
surges. This QLCS will likely lose much of its character and remain
sub-severe through the rest of the morning hours as instability
continues to gradually decrease and additional showers and weak
thunderstorms across southeastern MO into southwestern IL further
overturns downstream instability.

The QLCS convective line (what is left of it) is on track to exit
the CWA around 9 am, but stratiform rain and rumbles of thunder will
continue through much of the remainder of the morning along/east of
I-44 (MO) and I-55 (IL) until large-scale forcing pulls away and low
levels dry significantly. Additionally, a cold front will shortly
follow the QLCS with strong low-level CAA arriving in its wake and
gusty northwesterly winds of 20 to 30 mph at times. With clouds slow
to clear, dominant CAA will be cooling temperatures into the 40s and
50s F through the morning and early afternoon, approximately 30 F
cooler than 24 hours ago. CAA will continue through tonight with
temperatures in the 30s F by Sunday morning; however, winds will
remain strong enough to lower confidence in more than patchy frost
formation in locations that reach the mid-30s F.

On Sunday, a seasonably cool airmass will firmly be in place as a
surface anticyclone reaches the Mid-Mississippi River Valley during
the afternoon and evening. With strong insolation following
scattering stratocumulus by the afternoon, high temperatures are
forecast to warm into the mid-50s to low 60s F.

Pfahler

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 302 AM CDT Sat Apr 4 2026

In response to upper-level longwave troughing across the Great
Lakes, upper-level northwesterly flow will prevail over the Mid-
Mississippi River Valley late Sunday through late Tuesday navigated
by multiple shortwave troughs. In this pattern, a cold front will
pass southward through the CWA Monday morning into early afternoon,
providing a reinforcing round of low-level CAA. With differing
arrival times of this CAA, high temperatures along/south of I-70
will generally be in the 60s F and the 50s F to the north, but exact
values will be highly dependent on the timing of the front which
varies slightly in model guidance. This even colder airmass and
nearby anomalously strong surface anticyclone will lead to Monday
night/Tuesday morning featuring the coldest temperatures of the
forecast period with 30 to 60 percent probabilities of sub-32 F in
northeastern MO/west-central IL per the NBM. There is also a signal
for a frontogenetical band of precipitation to develop Monday night
into Tuesday with highest probabilities of measurable precipitation
in ensemble model membership across central and northeastern MO, 60
to 80 percent in 24 hours. With precipitation falling overnight and
the cold airmass, 20 to 40 percent of membership also has some of
this precipitation falling as light snow. These frontogenetical
bands are often difficult to resolve, especially at this time range,
leaving details hard to ascertain at the moment.

Wednesday through the rest of the upcoming work week, upper-level
flow will become quasi-zonal and permit low-level flow to become
southerly with temperatures warming back to above average. As Gulf
of Mexico moisture also eventually returns and potential shortwave
troughs traverse the Mid-Mississippi River Valley, ensemble model
membership with showers and thunderstorms gradually increases late
in the week.

Pfahler

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 619 AM CDT Sat Apr 4 2026

Flight conditions will improve by this afternoon as rain and a few
thunderstorms (mainly in southeastern MO/southwestern IL) end from
west to east, followed by scattering and lifting of MVFR and patchy
IFR ceilings. Westerly to northwesterly winds are anticipated to
occasionally gust 20 to 27 kt before slackening this evening and
gusts subside.

Pfahler

&&

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

$$

WFO LSX