Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241159

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
659 AM CDT TUE MAY 24 2016

Issued at 227 AM CDT Tue May 24 2016

Forecast challenge remains convective trends for the next few days
as the boundary layer becomes increasingly unstable and the large
scale upper air pattern becomes more southwesterly, allowing steep
mid level lapse rates to overspread the region. Weak shortwaves
ejecting from the main trof across the southwest CONUS will interact
with this unstable atmosphere to produce several rounds of
thunderstorms across the Midwest each day. Strong instability will
combine with adequate shear to keep a threat of severe thunderstorms
in the forecast every day.

Unfortunately, there really isn`t any surface feature to latch onto
to help determine convective coverage or location and therefore the
details of the forecast will hinge upon mesoscale features such as
outflow boundaries, subtle convergent zones and/or the remnants of
thunderstorms further west (including MCVs) in the short term (today
through Wednesday) and shortwave locations in the longer term.



.SHORT TERM... (Through Tonight)
Issued at 227 AM CDT Tue May 24 2016

MCV located across the eastern Ozarks/southeast Missouri has
been slowly marching east overnight and has had a few showers
associated with it. A handful of the convection allowing models
develop some thunderstorm activity with this feature toward sunrise,
while others do not. Of more importance is the convective complex
developing across north central Kansas at this time. Model guidance
is struggling on the details of how this feature evolves/moves
today. Some models advance it south-southeast into southwest
Missouri this morning essentially keeping the CWA dry, while others
march it east along I-70 into east central Missouri by this
afternoon/evening. Given the elevated nature of the convection and
its ties to the low level jet and location of the best instability
across the central/southern Plains I would suspect that this
activity will initially propogate toward southwest Missouri this
morning, but the residual outflow will help to initiate additional
convection further northeast along and south of I-70 this afternoon
as the atmosphere diurnally destabilizes. Some of these storms could
become strong/severe with large hail and damaging wind gusts being
the primary threats.

The diurnal activity should weaken with sunset and move east of
the area during the early evening. Next round of thunderstorms
should develop overnight as the low level jet intensifies and
another shortwave ripples across the region. This activity will be
centered further northwest though (thinking along and north of
I-70 in Missouri). These storms will have the potential of
producing large hail.


.LONG TERM... (Wednesday through Monday)
Issued at 227 AM CDT Tue May 24 2016

Convective trends become harder to pin down as much of it will
again depend on what occurs each night. At this point it appears
that the morning convection on Wednesday will move east and the
atmosphere may destablize enough for another round of
thunderstorms during the afternoon/evening, though more
isolated/scattered due to the weak ridging in the wake of the
overnight/early morning shortwave.

Pattern remains active through the weekend and into next week, with
chances of thunderstorms each day and temperatures remaining warm
with highs in the 80s each day.



.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 642 AM CDT Tue May 24 2016

Complex aviation forecast with lots of uncertainty in the
convection/precipitation trends. For this morning a few showers
will pass near KCPS and spotty showers may also impact KCOU. This
afternoon there is potential for a growing complex of thunderstorms
moving east-southeast with the northern portion impacting KCOU and
the St. Louis area terminals. It is possible as well the complex
may remain south of the terminals. I have mentioned VCTS given the
uncertainty. Overnight there is potential for another complex of
thunderstorms moving from the NW MO/SW IA region to the southeast
and impacting all of the terminals, especially KUIN and KCOU and
therefore have added -TSRA.

Specifics for KSTL:

VFR flight conditions expected this morning with showers expected
to remain south of the terminal. Watching potential for thunderstorms
later this afternoon as a growing complex of thunderstorms moves out
of western MO to the east-southeast. The northern portion may
impact KSTL, however it is possible as well the complex may
remain south of the terminals. I have mentioned VCTS given the
uncertainty. Overnight there is potential for another complex of
thunderstorms moving from the NW MO/SW IA region to the southeast
into eastern MO. Given the uncertainty and timing late in the TAF
period I have opted again for just VCTS.





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