Wentzville, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

438
FXUS63 KLSX 111928
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
228 PM CDT Fri Apr 11 2025

.KEY MESSAGES...

- Areas of frost are likely tonight particularly across parts of
  southwest and south central Illinois with lows in the mid to
  upper 30s. A Frost Advisory has therefore been issued for these
  areas.

- The weekend will be dry and warmer with temperatures rising into
  the 70s to low 80s.

&&

.SHORT TERM... (Through Sunday)
Issued at 224 PM CDT Fri Apr 11 2025

A long wave mid-upper level trough extending from southeastern Canada
all the way into the eastern Gulf will drift eastward through the
weekend.  Meanwhile, a high amplitude ridge currently moving off the
Rockies into the Plains will build into the Midwest Saturday, and
continue into the Great Lakes Region on Sunday.  This high amplitude
pattern pulled a relatively cool Canadian surface high down into the
Great Plains and Mississippi Valley last night.  The high will drift
east through the Mississippi Valley into the Ohio Valley over the
next 24 hours and then down into the southeastern U.S. on Sunday.
All this translates to a period of dry, quiet weather for the
weekend.

The surface ridge axis will be drifting through the Mid Mississippi
Valley tonight which will bring the area light and variable winds.
Forecast soundings show today`s clouds evaporating this evening, and
with light winds and a clear sky there should be excellent
radiational cooling.  Areas of frost are likely across parts of
Illinois where winds will remain light and variable or calm all
night, with temperatures falling into the mid 30s and high relative
humidity. Have therefore issued a Frost Advisory for parts of
southwest and south central Illinois for tonight.  The ridge axis
should be through central Missouri by 06-09Z and near or across the
Mississippi River by 12Z which will turn the wind around to the
south, so mainly patchy frost seems likely.  After the chilly start
to the day, southerly flow and rising heights aloft will push
temperatures back up into the 60s for most of the area, and up to
around 70 for parts of central Missouri.

The next upstream short wave trough is forecast to cross the Rockies
and move into the northern Plains Saturday night into Sunday
morning, resulting in low level cyclogenesis over the central
Plains.  The low will then move out of the Plains into the Midwest
during the day Sunday.  Persistent south to southwest flow will
continue to warm temperatures. Frost will not be an issue Sunday
morning with lows in the mid 40s to around 50.  Strong warm
advection during the day will push highs into the 70s for most areas
and low 80s across parts of central Missouri.

Carney

&&

.LONG TERM... (Monday through Next Friday)
Issued at 224 PM CDT Fri Apr 11 2025

The cold front associated with the low over the Midwest sweeps
through Missouri and Illinois by 18Z Monday.  Moisture return ahead
of the front looks minimal due to the blocking high over the
southeastern U.S. so the chance for any convection ahead of the
front is very low (<20 percent).  However medium range guidance is
showing strong frontogenesis in the cold sector, which wrings out as
much of 0.10 inch across northeast Missouri and west central
Illinois.  The LREF only shows about a 10 percent chance of that
much precip so the deterministic QPF looks pretty unlikely.

The progressive high amplitude pattern continues through the week.
Another short wave dives through the Midwest on Tuesday which phases
with the first wave over the eastern U.S.  This drags another cold
airmass into the Mississippi Valley, bringing another chance for
temperatures to drop into the 30s on Wednesday morning.  The
deterministic GFS and ECMWF diverge pretty sharply with another
system moving across the Plains into the Midwest and Great Lakes in
the Thursday -- Friday time frame.  Unsurprisingly, the LREF cluster
analysis is showing a great deal of variance with this system, with
strong bi-pole and monopole signals in the 500mb EOF patterns
indicating uncertainty in the speed and amplitude of the trough
respectively. Additionally, the interquartile range for high
temperatures Thursday and Friday is as much as 11 degrees.  However,
this system looks like the area`s best chance for more than a few
hundredths of precip for the next 7 days.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1231 PM CDT Fri Apr 11 2025

Areas of MVFR stratocumulus will continue to lift and scatter
through the afternoon. VFR flight conditions are expected to
prevail for the remainder of the period once the lower clouds
dissipate. Northerly flow will become light and variable this
evening then turn to the south Saturday morning.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...Frost Advisory from 3 AM to 8 AM CDT Saturday for Bond IL-
     Clinton IL-Fayette IL-Macoupin IL-Madison IL-Marion IL-
     Monroe IL-Montgomery IL-Randolph IL-Saint Clair IL-
     Washington IL.

&&

$$

WFO LSX