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000
FXUS63 KLSX 261756
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1256 PM CDT Fri Apr 26 2024

.KEY MESSAGES...

- An active weather pattern over the central U.S. will introduce
  multiple days with severe thunderstorm potential, including
  marginally severe hail, damaging winds and an isolated tornado.
  Much of the threat will remain over western portions of the
  forecast area until Sunday.

- Sunday remains the highest threat for severe thunderstorms ahead
  of an approaching cold front. Large hail, damaging wind, and
  tornadoes will all be a concern. Any thunderstorm will be
  capable of producing heavy rain with a localized flash flood
  threat.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 553 AM CDT Fri Apr 26 2024

A wing of mid-level warm air advection currently bisects the state
of Missouri with a strong 50-60 knot low level jet pointed into
western sections of the state. IR satellite shows robust cloud
development in this region with regional radar mosaics mapping
showers and thunderstorms from northwest Missouri to just west of
Columbia as of 09z this morning. While the CAMs have all had some
version of this activity, the HRRR seems to be handling this the
best so far. Activity is expected to to move northeast through mid-
morning underneath an area of upper level vorticity that advects
northeast. Thunderstorms are elevated and while MUCAPE values creep
up over eastern Missouri and western Illinois this morning, they are
substantially lower than the 1500+ J/kg values that exist over the
central Plains. This morning`s thunderstorms are expected to remain
sub-severe with small hail accompanying the strongest thunderstorms.

Severe weather potential this afternoon into tonight will rely on
development that takes shape over sections of western and
southwestern Missouri. Some of the potential activity is already
developing over northern Texas and Oklahoma, where yet another
mid/upper level disturbance continue to drive east-northeast around
the parent upper level trough. CAMs all show some version of a broad
mess of showers and thunderstorms moving into central Missouri by
mid-afternoon. The question then is the coverage and intensity of
thunderstorm activity as it runs into weaker instability (less than
1000 J/kg). Mid-level lapse rates of 6-7.5C edge into western
sections of the CWA but drop dramatically to the east will little,
if any, support along and east of the Mississippi River. It is
likely convection will weaken over eastern sections of the forecast
area. HRRR could be overselling thunderstorm intensity after 00z
with no surface forcing mechanism to support such. However, stronger
thunderstorms could produce marginally severe hail, damaging winds
and/or an isolated tornado. The main focus remains west, where yet
another round of surface based, discrete convection fires along the
front over eastern Kansas and moves into western Missouri. How this
activity impacts the region will largely depend on the preceding
round of convection, should it keep conditions cooler and more
stable east of the more discrete development to the west. It is more
plausible that the later development further west will weaken as it
approach central Missouri, if not die out entirely.

Trends are making Saturday look more tame than previously thought.
While high MUCAPE values cover the region, the warm front lifts to
the north with warm air aloft keeping the environment capped much of
the time. The upper low moves to the northeast with a void between
it and the next upper low that drive into the Plains for the later
half of the weekend. Warmer air aloft also keep the environment
capped with the absence of a strong surface forcing mechanism. Aside
from an isolate to widely scattered shower/thunderstorm along remnant
boundaries produced by prior convection, much of the daytime period
seems quite tame in comparison.


Maples

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 553 AM CDT Fri Apr 26 2024

The main concern in the long term period is late Saturday into
Sunday morning and again late Sunday afternoon into Sunday evening.
However, there are some trends that may be signaling a slowing cold
front and much later arrival than previously anticipated. This could
lend some challenges to thunderstorm potential as we get into the
late weekend and early next week.

This pattern makes the forecast sound more like a broken record with
repeated waves of showers and thunderstorms developing from the west
and tracking east into the local area. The difference by Saturday is
the broader area of greater instability that encompasses the region
as MUCAPES climb to around 3000 J/kg over central and northeast
Missouri. A more vigorous upper low closes off over the Four
Corners Region before taking a negative tilt and turning northeast
later in the weekend. The cold front remains well to the west, once
again triggering showers and thunderstorms over the Plains.
Deterministic guidance is not entirely aligned on the eastward
extent of convective potential late Saturday into Sunday with
varying strength in disturbances that eject northeast ahead of the
upper low. NAM is far weaker with next to nothing, while the GFS is
more aggressive and stronger with the leading shortwave providing
ascent over a broad region of instability. Even considering the more
aggressive GFS, thunderstorms edge into central and northeast
Missouri before decaying late Saturday night into Sunday morning.
Should this slightly westward trend continue, it may be enough to
keep most of the severe potential west of the forecast area. For
now, the far western extent of the CWA could see a strong to severe
thunderstorm late Saturday night into early Sunday, but confidence
is not high.

Sunday afternoon into Sunday evening has been the primary timeframe
when severe potential increases as the upper low tracks northeast
and gives some eastward push in the overall pattern. However, there
are now questions arising there, too. While the surface boundary
does edge closer to the area, there isn`t a real push of cold air
and the boundary itself doesn`t seem to clear the area entirely, if
at all. In fact, southerly flow persists into early Monday with
surface temperatures in the mid-50s to near 60 degrees and a
brief westerly component to surface flow


Maples

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1236 PM CDT Fri Apr 26 2024

Showers and a few thunderstorms will affect the terminals on and
off through early this evening. MVFR and some IFR ceilings and
visibilites will persist into early tomorrow morning, especially
with heavier downpours with thunderstorms. Winds will remain out
of the south to southeast with gusts in the 20 to 30 knot range.
Ceilings will improve to VFR on Saturday morning. There will be
some scattered showers and thunderstorms during the day on
Saturday, but the coverage will not be great enough to include the
the TAFs at this time.

Britt

&&

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

$$

WFO LSX