782
FXUS63 KLSX 020315
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1015 PM CDT Sun Jun 1 2025

.KEY MESSAGES...

- The warmest days of the week will be Monday and Tuesday when afternoon
  temperatures approach 90 degrees.

- An active stretch of weather kicks off on Tuesday and continues
  through the weekend, with multiple rounds of showers and
  thunderstorms capable of heavy rainfall expected.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 235 PM CDT Sun Jun 1 2025

Afternoon water vapor imagery shows northwesterly flow over the CWA,
with upper-level troughing over the eastern CONUS and a ridge
building over the Intermountain west. This northwesterly flow
continues to advect Canadian wildfire smoke into the region aloft,
which has been thick enough today to slightly mute the diurnal
temperature trend for several areas. Most locations in the CWA will
still see highs in the upper 70s to low/mid 80s, with the relatively
cooler temperatures being in Illinois behind the backdoor cold
front. This front is still expected to serve as the focus for
isolated to scattered convection across far southeastern Missouri
this afternoon and early evening, and cumulus has developed in this
area recently per visible satellite. Tall, skinny CAPE, poor low-
level lapse rates, and 0-6 km shear of 25 kts or less will keep any
updrafts that develop weaker and short lived.

The upper-level ridge will quickly build into the Midwest tomorrow,
with mid-level ridging proceeding it. This will turn mid-level flow
south-southwesterly and ramp up warm air advection, giving
temperatures a boost for tomorrow afternoon compared to today. Then,
most locations are forecast to reach the upper 80s. With the ridge
shifting eastward, steering flow will begin to push the wild fire
smoke further eastward, but not locally noticeably until Monday
night. Therefore, another day of milky skies can be expected
tomorrow, but smoke is still not forecast to reach the surface.

Elmore

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 235 PM CDT Sun Jun 1 2025

For Tuesday, guidance consensus is that an upper-level trough over
the western CONUS will slowly edge eastward as a shortwave rounds
its base across the Central Plains. Deep southerly to southwesterly
flow over the Middle Mississippi Valley will continue advecting
warm, moist air into the region ahead of an approaching front. This
will lead to one more day of temperatures in the upper 80s to around
90s for many locations, though specifics are still uncertain due to
variability in forecasted cloud cover and frontal timing. The
general timing of this front among guidance has quickened, with rain
chances associated with the low-level jet ahead of the front ramping
up across portions of central and northeastern Missouri already
Tuesday morning. The prefrontal environment Tuesday afternoon and
evening will be characterized by 30-35 kts of 0-6 km shear, though
there is quite a spread in SBCAPE, with a majority of ensemble
guidance having approximately 1,000 J/kg or less, though some
outliers and deterministic guidance have as much as 3,000 J/kg. This
leads to at least a low concern for strong to severe thunderstorms,
though mean flow and deep-layer shear parallel to the front and weak
CIN will lead to numerous updrafts interfering with each other,
limiting a severe thunderstorm threat. Though, given the slow-moving
nature of the front and the aforementioned wind profile, there is a
low concern for locally heavy rainfall late Tuesday into Wednesday.

For Wednesday through the weekend, guidance consensus breaks down on
the phasing of the trough, though some degree of quazi-zonal flow is
expected over the Middle Mississippi Valley. As long as the front
can remain in the vicinity of the CWA, this will lead to regular
chances of convection through the weekend as disturbances within the
flow ripple overhead. Given the lack of prolonged warm air advection
and frequent rain/cloud chances, the 75th percentile of ensemble
guidance struggles to break 80 degrees for much of the CWA through
Sunday.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1012 PM CDT Sun Jun 1 2025

No significant changes made to the 06Z TAF cycle, as VFR
conditions remain most likely to prevail throughout the period.
There is a low probability potential for shallow fog to impact
river valley sites late tonight and early tomorrow morning,
particularly JEF/SUS. However, the chance of visibility reductions
and terminal impacts remains too low for explicit mention in the
TAFS at this time. Otherwise, light and variable winds will become
southerly tomorrow morning, and may be occasionally gusty at
COU/JEF/UIN in the afternoon.

BRC


&&

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

$$

WFO LSX