380
FXUS63 KLSX 011948
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
248 PM CDT Sat Jun 1 2024

.KEY MESSAGES...

- Showers and isolated thunderstorms will diminish by early this
  evening, with areas of fog possible overnight into early Sunday
  morning.

- Unsettled weather returns late Sunday night and persists into
  midweek with nearly continous chances for showers and
  thunderstorms, however no all day rains. Temperaturs will
  largely be above normal during this period.

- A pattern change will result in cooler temperatures, near to
  perhaps slightly below normal, during the later part of the
  week and into early next weekend.

&&

.SHORT TERM... (Through Sunday Afternoon)
Issued at 157 PM CDT Sat Jun 1 2024

The axis of the mid level trof and attendant surface trof were
near the MS River early this afternoon. The best coverage of
showers were along and to the east of them, with scattered showers
back into the cyclonic flow west of the MS River. Despite SBCAPE
of 750-1500+ J/KG centered in roughly the same region across far
eastern MO and western IL we have yet to see any thunder,
seemingly owing to the lack of more vigorous updrafts. The threat
of showers and perhaps still a rumble of thunder will persist
across eastern MO into western IL through the remainder of the
afternoon into early evening, sliding east with time in concert
with the advancement of the upper and surface trofs with activity
dissipating in IL this evening with loss of heating.

For the remainder of tonight we will see diminishing clouds across
portions of central and eastern MO, while clouds should persist
longer along and to the east of the MS River. The clearing clouds
in the western CWA along with light winds and the recent rainfall
seem like a pretty good recipe for fog overnight into Sunday
morning. We will need to monitor this tonight as it`s certainly
possible we could see some locally dense fog.

Weak surface ridging will generally dominate on Sunday. After the
dissipation of the morning fog, we should see cumuliform clouds
and warmer temperatures that will be closer to normal. There is a
small chance of showers and thunderstorms in central MO late in
the afternoon associated with a weak impulse in the quasi-zonal
flow and perhaps an old boundary originating in the Plains.

Glass

&&

.LONG TERM... (Sunday Night through Next Saturday)
Issued at 157 PM CDT Sat Jun 1 2024

A more unsettled pattern will unfold late Sunday night and
persist into midweek. Sunday night through Tuesday, a series of
weak migratory short waves in the quasi-zonal flow will bring
thunderstorm chances to the area. On Sunday night we actually
could see precipitation in two ways: Scattered WAA LLJ driven
showers and thunderstorms late across parts of eastern MO and
western IL, and/or a decaying Plains MCS and associated boundary
moving into the area late. This remnant boundary or re-energized
MCS seems like it will be a catalyst for additional showers and
thunderstorms on Monday and perhaps into Monday night, especially
as the day progresses and it interacts with an increasingly
unstable air mass. Otherwise a more prominent northern stream
short wave trof that will be the impetus for a pattern change
will bring a threat of showers and thunderstorms as it and the
associated cold front traverse the region late Tuesday-
Wednesday. While there are some timing differences in the cold
front passage on Wednesday, present indications are the highest
POPs will be centered on Tuesday afternoon and night.

The deterministic and ensembles are coming into better agreement
later next week and into next weekend with the ensuing pattern
change and development of an upper low in the vicinity of the
Great Lakes with a broad trof extending southeastward through the
Middle Atlantic. As mentioned yesterday this will result in
northwest flow across our area during the later half of next week
and into early next weekend. The above normal temperatures for the
Monday-Wednesday period will be replaced by near to perhaps
slightly below normal temperatures Thursday-Saturday as a series
of weak short waves in the northwest flow bring periodic surface
trofs or weakly defined cold fronts through the region. There are
a lack of strong signals for precipitation during this time frame
but the flow regime suggests that it certainly can`t be ruled out.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1232 PM CDT Sat Jun 1 2024

Scattered showers will primarily impact KUIN and the St. Louis
area terminals this afternoon with the best thunder potential from
around 20-22z. Flight conditions will largely be MVFR. Between
22-00z the majority of the showers should move east of the
terminals with this activity decaying early this evening across SW
IL. Flight conditions should at least temporarily improve to VFR
across much of the area this evening, but overnight we will see a
mix of fog and lower stratus that lasts into mid Sunday morning.
The visibility in the fog could certainly be lower at KCOU and
KJEF that the current forecast near 1SM. By mid-late morning on
Sunday, fog should have dissipated and ceilings should be
improving.

Glass

&&

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

$$

WFO LSX