430
FXUS63 KLSX 032334
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
634 PM CDT Thu Jul 3 2025

.KEY MESSAGES...

- Seasonably warm and relatively humid conditions will persist
  through Saturday with afternoon heat index values reaching the
  mid-90s to near 100 F.

- Largely dry conditions will persist into Saturday, including
  the 4th of July. Saturday evening into next week, there will be
  multiple opportunities for showers and thunderstorms.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 221 PM CDT Thu Jul 3 2025

An upper-level ridge, currently positioned over the Central/Northern
Plains this afternoon, will shift eastward into the Mississippi
River Valley tonight through Friday/4th of July. Large-scale
subsidence generated by this incoming ridge and a capping
inversion will keep the chance of any isolated afternoon shower or
thunderstorm low (less than 15 percent) with "convection" likely
limited to just diurnal cumulus and altocumulus this afternoon/
evening and Friday. As a surface anticyclone departs, low-level
flow will also become more southerly by Friday, aiding the ongoing
gradual warming trend with high temperatures around 90 to the
mid-90s F nearly CWA-wide. With increasing moisture, dewpoints
will also be slightly rising overall, but deep BL mixing during
the afternoon will limit peak heat index values in the mid-90s to
near 100 F.

Pfahler

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 221 PM CDT Thu Jul 3 2025

The upper-level ridge will continue eastward into the Great Lakes
and Mid-Atlantic while de-amplifying over the holiday weekend,
allowing a weakening trough to traverse the Mid-Mississippi River
Valley late Saturday into Sunday, accompanied by a weak cold front
on Sunday. Around 20 to 40 percent of ensemble model membership have
showers and thunderstorms reaching/developing across central,
northeastern MO and west-central IL Saturday evening into night.
However, on Sunday more focused low-level forcing with the cold
front and less convective inhibition leads to 40 to 60 percent of
membership depicting showers and thunderstorms over a larger
portion of the CWA. That being said, it is not particularly clear
what the coverage will be given that large-scale forcing will not
be strong. With very weak deep-layer wind shear (~10 kt),
unorganized, pulse thunderstorms are expected which could contain
localized gusty winds and downpours, but organized severe
thunderstorms are unlikely. Saturday`s temperatures are forecast
to be similar to Friday, except slightly cooler across
northeastern, central MO and west-central IL with greater clouds
and shallower BL mixing. On Sunday, high temperatures should be
slightly cooler across much of the CWA but confidence in exact
values is lower due to the presence of the front and showers and
thunderstorms.

Through next week, global model guidance is in general agreement
that time-mean upper/mid-level flow will make a gradual transition
from quasi-zonal to northwesterly with some semblance of Sunday`s
front wavering around the Mid-Mississippi River Valley. This pattern
will be favor multiple opportunities for showers and
thunderstorms as a series of mid-level perturbations or MCVs
traverse this flow; however, the timing of these features and the
location of the front at any given time is uncertain. Throughout
next week ensemble model-based probabilities of showers and
thunderstorms vary between 20 and 60 percent, although there
appears to be a relative minimum Monday night/Tuesday morning with
a signal for the front to shift south of the CWA and the region
to be between waves. NBM interquartile high temperature ranges
have narrowed for next week to around 3 to 5 F, closing in on
approximately average, but if there are more widespread
precipitation and clouds any of those days, temperatures could
easily end up even cooler.

Pfahler

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 632 PM CDT Thu Jul 3 2025

High pressure over the region provides light or calm winds and VFR
conditions. The main concern is the potential for valley fog, but
a warm evening and relatively low dewpoints is expected to prevent
significant fog from occurring.

Kimble

&&

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

$$

WFO LSX