199
FXUS63 KLSX 140335
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1035 PM CDT Mon May 13 2024

.KEY MESSAGES...

- A slow-moving upper trough will bring waves of showers and
  scattered thunderstorms to the region through Tuesday
  afternoon. An isolated strong storm with gusty winds and small
  hail remains possible through this evening, mainly from central
  into southeast Missouri.

- After Tuesday evening, shower and thunderstorm chances will
  return late Wednesday through Friday.

- Above normal temperatures will return for the upcoming weekend.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 225 PM CDT Mon May 13 2024

A slow-moving upper trof and low will produce unsettled weather
across the region through Tuesday evening as it progresses
eastward into and through the Mississippi Valley. A series of vort
maxes rotating through the trof along with diurnal heating will
modulate the greatest precipitation chances and coverage during
this time frame, however lesser precipitation chances will exist
the entire duration.

The first better defined vort max will rotate northeast across the
CWA the remainder of this afternoon into early evening bringing a
better organized band/wave of showers and some thunder. Thus far
thunder has been at a minimum. Despite areas of weak surface-
based CAPE of generally 1000+ J/KG, weak lapse rates and a good
deal of low-mid level moisture have diminished MLCAPE, which
seems to be a limiting factor thus far. There is a low chance of a
strong storm through early evening, primarily across central and
southeast MO, owing to slightly better deep layer shear, however
the moist conditions and low DCAPE are not very favorable. There
should diminishing coverage of precipitation to more scattered
later this evening and overnight with an additional vort max
tracking eastward providing some impetus. The moist low-levels and
light winds are also a recipe for fog/stratus.

The vertically stacked system and surface front will slide to the
east on Tuesday and into the eastern Ohio Valley by early evening.
Muted diurnal heating from breaks in the cloud cover should lead
to an uptick in instability and the coverage of showers and some
thunder on Tuesday afternoon. Precipitation chances should wind
down on Tuesday evening as the upper trof continues to progress
east into the Ohio Valley, potentially with fog/stratus in it`s
wake into Wednesday morning.

Glass

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 225 PM CDT Mon May 13 2024

An elongated and progressive northern stream upper trof will
bring the next organized chance of showers and thunderstorms in
the late Wednesday through Friday time frame. Differences in
position and timing of short waves moving through the mean upper
trof are resulting in probably a longer window of precipitation
chances in the forecast than reality. The initial chance of
showers and storms could as early as Wednesday night depending on
the position of a lead vort max and forcing via a southwesterly
LLJ along with a returning warm front. There is better agreement
that the chance of showers and thunderstorms will peak Thursday
morning through the afternoon into early evening along and ahead
of an advancing cold front.

A southern stream upper trof could linger the rain chances longer
into Friday or early Saturday but there is a decent amount of
spread in the specifics of the trof speed/structure with the LREF
cluster analysis showing four variations in the larger scale flow,
and thus lower predictability. It does appear we should see
temperatures return to above normal for the upcoming weekend with
the NBM showing the entire IQR above normal.

Glass

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1033 PM CDT Mon May 13 2024

Lots of moisture still lingering across the area tonight as a
broad low pressure system slowly tracks near the region. Multiple
subvortices have brought rounds of showers and embedded
thunderstorms, though these may not be as widespread as previously
thought. Conditions are variable across the region from VFR to
MVFR, but the trend will be for conditions to worsen overnight as
ceilings lower. With so much moisture around and subtle low level
lift with the low, we couldn`t rule out some light fog or drizzle
as well, but lower ceilings at least look likely. We`ll see some
improvement Tuesday morning, but another round of afternoon
showers and thunderstorms is expected just about area wide as
winds become northwesterly on the back side of the finally
departing low.

Kimble

&&

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

$$

WFO LSX