766
FXUS63 KLSX 261108
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
608 AM CDT Fri Jul 26 2024

.KEY MESSAGES...

- Shower and thunderstorm chances will ramp up this weekend with
  the potential for localized heavy downpours at times.

- Hot weather will return to the region next week. Heat index
  values will approach dangerous levels at times. Occasional
  rounds of thunderstorms may bring periods of relief.



&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 337 AM CDT Fri Jul 26 2024

The weak frontal boundary across southern Missouri will be the
main focus for any activity today. However, would not be surprised
if isolated storms pop up further north, though a majority of
area will be dry. Despite MU CAPEs between 1500-2500 J/kg,
especially near the frontal boundary, there will be little to no
shear and weak forcing, so do not expect any severe weather today.
As for temperatures today, they will be a bit lower than
yesterday (mid to upper 80s) but with dewpoints still in the mid
60s to low 70s it will still be a bit humid across the region.

Activity will weaken and diminish after sunset with dry conditions
for the remainder of the overnight hours. Lows will be near normal
in the 60s.

In the meantime, as the northern portion of the upper level ridge
across the Upper Midwest shifts to the east, the cutoff upper low
over the Arklatex region will begin to lift northward towards the
KS/MO border by midday Saturday. So with increasing low level
moisture as well as instability, will see increasing chances of
showers and storms as several shortwaves move through the area
Saturday. PWATs between 1.5 and 2 inches will advect into the area
on Saturday, with the latest HREF indicating that a majority of the
ensemble members have PWATs greater than 2 inches, mainly along and
south of I-70. So storms that do form will have the potential for
localized heavy downpours, thus could see isolated flash flood
threat due to the weak steering flow aloft. Temperatures on
Saturday will be a bit cooler due to increased cloud cover and
precipitation.

Byrd
&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 337 AM CDT Fri Jul 26 2024

By Sunday, the upper level low will begin to slide off to the
northeast and exit the region by late Sunday night. In the meantime,
lingering shortwaves will slide through the area, generating
additional rounds of showers and thunderstorms Saturday night
through Sunday. The axis of higher PWATs will shift to the east by
Sunday with best chances for localized heavy downpours east of
the Mississippi River. Highs will be in the 80s on Sunday due to
the lingering cloud cover and precipitation.

In the meantime, the latest LREF cluster analysis has pretty good
agreement among the ensemble members with the western portion of the
upper level ridge sliding to the east towards the forecast area. So
even though we will not be directly under the main ridge axis, we
will experience a decent warm up with highs in the low to mid 90s by
Tuesday, then into the mid to upper 90s by Wednesday and Thursday.
This combined with dewpoints in the 70s, will create heat index
values between 100 and 105 beginning on Tuesday. However, we will
have the potential for ridge runners as thunderstorms track around
the periphery of the ridge. So even though rain chances will be on
the low side each day, if, when and where these storms do occur
local heat relief is likely, but would see conditions rebound once
the precipitation exits.

Byrd
&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 605 AM CDT Fri Jul 26 2024

Patchy fog has developed early this morning in river valleys and
low lying areas, so kept mention of MVFR visibilities at KJEF,
KSUS and KCPS through 13z. Otherwise, light east winds through the
forecast period with scattered diurnal cu. Best chances of rain
will stay south of TAF sites at this time, so kept TAFs dry for
now.

Byrd
&&

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

$$
WFO LSX