793
FXUS63 KLSX 061057
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
557 AM CDT Sun Jul 6 2025

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms are expected
  this afternoon into early evening across central and eastern
  Missouri into southwest and west central Illinois. Some storms
  could produce locally heavy downpours and gusty winds.

- Seasonably warm and humid weather will continue into the work-
  week with a chance for mainly afternoon and evening showers and
  thunderstorms.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 357 AM CDT Sun Jul 6 2025

Ongoing convection is being fueled by moisture convergence driven by
a weak low level jet ahead of a cold front which is moving into
Missouri this morning.  The front will continue to sag southeast
today, driven by a short wave trough moving moving through the
Midwest. This front will continue to be a focus for convection today
and tonight as it drifts southeast into the forecast area.  Guidance
is somewhat divided on convective trends this morning, with some
models showing storms dissipating by 12-14Z, and others showing
isolated to widely scattered showers and storms continuing through
the morning hours.  However, there is consensus in increasing
coverage this afternoon along and ahead of the cold front across
central and southeast Missouri into southwest and south central
Illinois. The 60-70 PoPs in the going forecast continue to look good
for this afternoon, with decreasing PoPs in the evening as diurnal
heating wanes.  Short range guidance shows the front stalling
tonight somewhere between I-70 and I-44 in Missouri, and just south
of I-70  in Illinois.  Isolated to widely scattered showers and
storms will likely continue overnight due to low level moisture
convergence in the vicinity of the front.  Localized heavy downpours
and possible wet microbursts continue to be possible with these
storms.  Temperatures this afternoon should be a few degrees cooler
than Saturday due to more cloud cover and afternoon storms.

Carney

&&

.LONG TERM...  (Monday through Saturday)
Issued at 357 AM CDT Sun Jul 6 2025

There`s been little change to the forecast for Monday through next
Saturday.  The front remains nearly stationary near or just south of
I-70 for much of the day.  However the position of the effective
boundary will most likely be controlled by convection/outflows
through the day.  While convection in the vicinity of the front on
Monday, the coverage is questionable with some models showing
widespread QPF along and south of the front, and others (including
most CAMs) keeping coverage more in the 20-50% range.  Currently
leaning toward the 20-50% range given the uncertainty in frontal
position, but this may need to be increased in subsequent forecasts.

The next upstream short wave move from the Plains into the Midwest
Tuesday, which along with the lingering front, will produce more
thunderstorms.  The deterministic GFS continues to look like it`s
contaminated with convective feedback, however it`s showing 2300+
J/Kg MLCAPE at 18Z Tuesday across parts of western and central
Missouri, and this agrees well with LREF mean SBCAPE.  Inverted V
forecast soundings indicate the possibility of wet microbursts, but
the 0-6km shear is only 15-20kts.  While there could be a few
strong/severe storms, organized severe storms are unlikely due to
the lack of strong deep-layer shear.

Weak northwest to occasional zonal flow continues for the rest of
the work-week as the upper pattern is first amplified by Tuesday`s
short wave, and then the southwest upper ridge is attenuated by
another wave which moves across the northern 1/2 of the CONUS and
southern Canada Friday and Saturday.  Sensible weather at the
surface will change little during this period, with mostly afternoon
and evening convection driven by diurnal heating.  Temperatures look
seasonably warm and humid with highs mainly in the upper 80s to low
90s.  There may be some relief from the heat Saturday if the
aforementioned shortwave digs farther south into the Midwest or
Great Lakes which would push the associated cold front farther into
the Mississippi Valley.


Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 548 AM CDT Sun Jul 6 2025

The primary concern today is convection along and ahead of a
slow- moving cold front. An isolated shower or thunderstorm is
possible at almost any time across most of the forecast area
through Monday morning. However, more widespread thunderstorm
development is expected this afternoon across central, east
central, and southeast Missouri into southwest and south central
Illinois. Thunderstorms will be capable of reducing the visibility
to 2SM or less in heavy downpours, and gusty winds of 30-40kts.
Thunderstorms should weaken and become less numerous between
02-04Z. Otherwise, VFR flight conditions are expected to prevail
outside of thunderstorms.

Carney

&&

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

$$

WFO LSX