186
FXUS63 KLSX 281201
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
701 AM CDT Sun Apr 28 2024

.KEY MESSAGES...

- A line of showers and thunderstorms will move east out of
  west/southwest Missouri this morning and is expected to weaken
  in time.

- Additional showers and thunderstorms are expected along a cold
  front this afternoon into late this evening. A few thunderstorms
  could be severe with marginally severe hail, damaging winds and
  an isolated tornado or two.

- The front will stall over the region Monday with showers and
  sub-severe thunderstorms over sections of southeast Missouri
  and southwest Illinois. The front returns north with warmer than
  normal conditions continuing through the upcoming week.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 413 AM CDT Sun Apr 28 2024

Key Messages:

- A line of showers and weakening thunderstorms will move east out
of western Missouri this morning and continue to decay as the line
approaches the Mississippi River.

- Additional thunderstorms are expected along a cold front this
afternoon into late this evening. A few thunderstorms could be
severe with marginally severe hail, damaging winds and an isolated
tornado or two.

- The front will stall over the region Monday with showers and sub-
severe thunderstorms over sections of southeast Missouri and
southwest Illinois. The front returns north with warmer than normal
conditions continuing through the upcoming week.

Radar trends show precipitation over northeast Missouri and west-
central Illinois, remnant of overnight convection that quickly
decayed as it encountered a less favorable environment over eastern
sections of Missouri. In fact, very little lightning is being
detected within this area and what thunderstorms remain are further
west with the next round of approaching precipitation.

The the focus shifts to western Missouri where another line of
weakening thunderstorms are progressing eastward early this morning.
Given the diurnal minimum and thunderstorms that preceded the
incoming activity, further decay is expected as the line departs the
origin of instability and moves into air that has been largely
stabilized by preceding thunderstorms. Though this activity is
expected to be sub-severe as it enters the CWA this morning,
rainfall and cloud cover could eat into potential for instability to
recover this afternoon, when redevelopment is possible along the
approaching cold front.

This afternoon`s thunderstorm potential could very well be to be
conditional upon the survival and geographic spread of the lingering
rainfall that is ejecting out of western Missouri. The upper level
low continues to track into the northern Plains with the surface low
slightly to the southeast over western Iowa. The trailing cold front
begins to slow, presenting less of a convergent focus as it moves
into central Missouri. Upper ascent becomes more fragmented in the
vicinity of the surface front, along with marginal MUCAPE values
around 1000 J/kg encompassing much of the state of Missouri. Mid-
level lapse rates of around 7C are more respectable than in previous
days, but highest values reside over south-central Missouri around
the time convective initiation is favored between early and mid-
afternoon. RAP model sounding show skinny CAPE profiles closer to
the Mississippi River, suggesting hail may not be much of a threat,
if any at all, as thunderstorms approach the St. Louis Metro area.
The one favorable parameter are 0-6km shear values that are at 40-50
kts ahead of the front, along with a strengthening LLJ.

All of this suggests that redevelopment will once again be focused
to our west, closer to the slowing front. This leaves a limited
window of opportunity to organize behind the preceding rainfall and
prior to waning diurnal maximums with much of the surface air
already being rain-cooled over central Missouri. Should strong to
severe thunderstorms develop this afternoon, their peak intensity
may be over western portions of the CWA. Should hail be a concern,
it will be with initial discrete development, which then transitions
to a damaging wind threat as convection become linear. An isolated
tornado or two may be embedded in the line with backed winds ahead
of the approaching line. Confidence in severe weather is low given
all of the potential caveats ahead of the redevelopment.

Guidance has been consistent in stalling the front over southern
sections of the forecast area Monday. This becomes the focus for
scattered, sub-severe thunderstorms over  sections of southeast
Missouri and southwest Illinois Monday afternoon.


Maples

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 441 AM CDT Sun Apr 28 2024

The pattern continues to look warm and active over the upcoming
week. Surface high pressure quasi-zonal flow lends potential for
one quiet and dry day Tuesday before mid and upper level
amplification commences through midweek. The initial topic will be
the warming temperatures as southerly return flow leads to well
above normal conditions Tuesday into Wednesday. NBM spread
continues to point at temperatures that could inch within a few
degrees of record highs Wednesday. The key will be the evolution
of a broad upper trough over the Intermountain West, which becomes
a slingshot for multiple shortwaves that eject out of the
southwest into the central U.S. The consequence is what looks to
be an increasingly active week over the Plains and Midwest. A
cold front begins to approach the region from the northwest late
Tuesday or Wednesday. While the front initially hangs up at the
northwest periphery of the southeast ridge, thunderstorm
potential increases as the front draws near. Guidance then begins
to spread as there is less agreement on the progress of the front
and evolution of the synoptic setup through the later half of the
week.

Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 650 AM CDT Sun Apr 28 2024

Metro terminals remain well east of decaying showers and
thunderstorms that are tracking into section of central and
northeast Missouri, as well as west-central Illinois. Given slow
eastward movement and rate of weakening, metro terminals should
remain VFR for much of the day with gusty southerly winds being
the primary impact.

Central Missouri terminals, along with KUIN, are on the edge of
showers and isolated thunderstorms. Much of the lightning has
decreased considerably in the couple of hour leading up to the 12z
TAF package. Showers an intermittent lightning activity will move
over KCOU/KJEF and KUIN through the morning hours with the
potential to bounce between low VFR/high MVFR ceilings. Pockets of
moderate shower activity and/or more persistent rainfall will also
lead to marginal visibility reductions.

Early morning activity could curb instability recovery for this
afternoon through late this evening. There is uncertainty in how
intense thunderstorms may get, but latest trends are favoring less
in the way of stronger thunderstorms. Nonetheless, impacts will be
similar to that of late night and this morning with weakening
showers and thunderstorms move west to east. MVFR conditions are
largely expected to accompany thunderstorms with pockets of IFR
possible within isolated stronger cells. Much of the activity
will move east of the terminals late in the TAF period.

Maples

&&

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

$$

WFO LSX