174
FXUS63 KLSX 281735
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1235 PM CDT Sun Apr 28 2024

.UPDATE...
Issued at 835 AM CDT Sun Apr 28 2024

Regional radar mosaic depicts a decaying convective linear
structure tracking into eastern Missouri, with a stratiform rain
shield to its west behind the storm motion. Satellite imagery
paints widespread clouds across the region, and objective surface
analysis shows limited low-level moisture within the open warm
sector of a sluggish surface low.

All of the above factors are leading to a rather drastic decrease
in the threat for severe convection across the bi-state area
today. Instability is being drastically overestimated by high-
resolution guidance, and there is little to no support in the real
atmosphere for a significant recovery in this energy. Behind the
weakening showers, we may be able to destabilize enough ahead of
the approaching cold front to support marginally-severe
thunderstorms at the worst this afternoon and evening. This
potential will continue to be monitored through the day, but it is
entirely possible that no severe weather occurs.

MRB

&&

.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 18z TAFs through 18z Monday Afternoon)
Issued at 1218 PM CDT Sun Apr 28 2024

Widespread cloud cover of varying heights are currently impacting
the regional terminals, with CIGs as low as 2kft and as high as
10kft observed. The region is well-within the warm sector of a
surface low that is slowly moving northeast in the central Great
Plains. A few weak showers are all that`s left from overnight
convection, and are slowly eroding.

The potential for stronger thunderstorms late this evening into
tonight is diminishing quickly, owing to the abundant cloud cover
limiting instability. The catalyst for convection will be the cold
front, currently far from the region in east-central Kansas and
eastern Nebraska. The boundary will eventually track east, leading
to showers and a few thunderstorms from west to east tonight.
Winds gradually shift out of the west behind the front, with a
period of MVFR CIGs forecast overnight into the early morning
Monday. However, drier air and diurnal heating will help erode the
lower CIGs and allow for VFR conditions to resume.

MRB

&&

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

$$

WFO LSX