451
FXUS63 KLSX 281800
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
100 PM CDT Fri Jun 28 2024

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms are expected today
  through Saturday evening. A few thunderstorms could be severe
  tonight and again Saturday afternoon into Saturday evening. The
  main threats will be damaging winds and large hail. These
  threats are highest over central Missouri tonight. The threats
  are relatively low otherwise.

- Above normal temperatures are expect through Saturday. Cooler
  than normal temperatures Sunday and Monday will be bookended by
  above normal temperatures as warmer conditions return Tuesday.


&&

.SHORT TERM...  (Through Late Saturday)
Issued at 351 AM CDT Fri Jun 28 2024

A broad view of the CONUS shows surface high pressure over the
eastern Great Lakes early this morning. The eastward nudge in the
surface ridge has resulted in southeasterly surface flow locally,
progressively turning more southerly behind a warm front that is
expected to slowly lift northward today. IR satellite shows much of
the central sections of the U.S. covered by broken to overcast skies
as a few clusters of thunderstorms are dispersed about the central
section of the nation.

While the aforementioned warm front resides at the surface, weak mid-
level warm air advection at the back side of the ridge has resulted
in a few showers grazing northern sections of Missouri. No lightning
is associated with this activity with little or no CAPE over the
area. Meanwhile, a more robust area of showers and thunderstorms
line up from Oklahoma into the Upper Midwest. Resulting cloud cover
will continue to stream east through the day. One feature to watch
will be the potential for an MCV to track from the Plains into
northern Missouri during the late morning and early afternoon.
Showers and a few thunderstorms are likely to skim the northern, but
the highest chances remain over north-central Missouri into
southeast Iowa. Despite the warm front and southerly flow, cloud
cover and any additional precipitation should hold temperature in
the 80s north of I-70. It`ll be a touch warmer to the south with low-
90s.

A broad trough traverses the Canadian/U.S. border through the day as
the upper ridge flattens over the Midwest. The western periphery to
the mid-level ridge also shifts slightly east with strong moisture
advection driven into western sections of Missouri late this
evening. An upper level shortwave approaches with signals that a
rather compact LLJ takes aim at western sections of the state. A
pool of higher MUCAPE in the 2500 to locally 4000 J/kg reside over
eastern Kansas and western Missouri, along with 35-40 knots of 0-6km
shear. This will be the initial area to focus for thunderstorm
development late this evening into the overnight hours. While
thunderstorms are more likely to be severe in their origin, CAPE and
shear values quickly drop to the east. This should result in a
weakening trend in the overnight period with limited support for
severe potential with time.

Thunderstorms shift southeast through Saturday morning, far less
likely to be severe as they approach I-70. How quickly the area can
recover will depend on how quickly activity decays and/or exits east
Saturday morning. The front will then become the focus for
additional convective potential Saturday afternoon and evening. The
boundary lines up along or just south of I-70 and is largely
supported by mid-level vorticity with the lack of upper level
ascent. Guidance suggests surface instability could recover quickly
with MLCAPE of 3500-4000 J/kg. The limiting factor is rather weak
flow with shear only about 20-30 knots. Given better mid-level lapse
rates of near 8C and thicker CAPE profiles on modeled soundings,
large hail could be a threat with initial development, along with
damaging winds with collapsing updrafts.

Maples
&&

.LONG TERM...  (Sunday through Thursday)
Issued at 351 AM CDT Fri Jun 28 2024

The cold front shifts south of the area Sunday as surface high
pressure builds north to south from the Plain and upper level
ridging begins to amplify over the central U.S. Northerly flow as
the surface and northwest flow aloft will shunt higher dewpoints
south with upper 60s to mid-70s being replaced by 50s to low-60s
Sunday. 850mb temperatures in the mid-teens will make for a rather
nice day relative to recent conditions. These conditions persist
into Monday as the surface high slides east with easterly surface
flow pushing dewpoints in toe the upper 40s to mid-50s. Highs
ranging from the upper 70s to mid-80s may even feel refreshing.

The surface high and upper ridge will stave off any precipitation
potential as active weather curves around the area to the west and
the north until at least midweek. Surface high pressure moves into
the Atlantic Region with southerly return commencing Tuesday with
warmer air advecting back into the area. The upper level ridge
begins to flatten over the central U.S. in a similar fashion as is
does late this week. Vorticity is ejected around the western
periphery of the upper ridge once again as a broad upper trough
moves west to east over the Canadian/U.S. border. This pushes a cold
front into the Midwest Wednesday with the front showing a tendency
to slow as it moves south. This introduces additional chances for
showers and thunderstorms from mid to late week.

Maples
&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1258 PM CDT Fri Jun 28 2024

Isolated showers and a few storms this afternoon for KCOU, KJEF
and KUIN. Otherwise, VFR flight conditions until activity develops
over western MO and slides east and southeast tonight. Showers and
storms will move into KUIN, KCOU and KJEF between 04z and 06z
Saturday, while not until 09z-10z Saturday for St. Louis metro
area TAFs. Activity will then diminish and move out between 11z
and 14z Saturday.

As for winds, they will remain from the south for a majority of
the forecast period. However, they will veer to the southwest to
west at KUIN, KCOU and KJEF by 16z Saturday as cold front
approaches area.

Byrd
&&

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

$$
WFO LSX