Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 301800

100 PM CDT Sat Aug 30 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 330 AM CDT Sat Aug 30 2014

Regional radar is showing a number of areas of showers and
thunderstorms across Missouri and western Illinois early this
morning. These are generally within a weak warm advection regime
ahead of a upper trof moving through the MS Valley and in advance
of the attendant cold front. While all the current activity should
continue moving east northeast this morning, the overall consensus
amongst the guidance and convection allowing models is that there
should be a general increase in the scattered activity currently
over southwest Missouri as the morning progresses and it moves
northeast. Additional development is also expected during the
later part of the morning into the afternoon in a broad southwest
to northeast zone ahead of the slowly advancing cold front and centered
through the southeast half of the CWA. Given the current temperatures
in the 70s, low-mid 80s looks reasonable for highs today.


.LONG TERM:  (Tonight through Friday)
Issued at 330 AM CDT Sat Aug 30 2014

Convective trends are not completely clear cut tonight. The main
upper trof axis should have passed to the east by early this
evening, but there is a weak lingering vort max still to pass and
the front appears to wash out across northeast Missouri and west
central Illinois. Sans the NAM, the model consensus keeps a chance
of showers and thunderstorms centered though the southeast half of
the CWA during the evening. Sunday looks largely dry and warmer
with possibly some isolated diurnal storms across southeast MO and
southwest Illinois. The threat of organized covection should
slowly spread into northeast Missouri late Sunday night with the
approach of a progressive long wave trof and attendant cold front and
intensifying southwesterly LLJ. Thunderstorms appear likely on
Labor Day and Monday night as the cold front moves slowly southward
into a moist unstable air mass, and as a southwesterly LLJ and the
upper trof contribute to lift and cap removal. This system will be
accompanied by deep layer shear of 30-40+ knots resulting in the
potential for organized severe storms. Showers and thunderstorms
could persist across the southern CWA Tuesday and maybe even into
Tuesday night and Wednesday in the vicinity of the front and then
as it retreats back northward late Wednesday.

Late in the week ahead the upper ridge is forecast to restablish
itself over the southeast half of the Nation, bringing a return of
more summer like weather/heat.



.AVIATION:  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1240 PM CDT Sat Aug 30 2014

A trough of low pressure extending from north central Missouri
southwest into southeast Kansas will remain nearly stationary
today. This trough will provide a focus for thunderstorm
development across the area through the afternoon into early
evening. Expect scattered to numerous showers and thunderstorms
this afternoon...primarily east of the trough. MVFR/IFR flight
conditions can be expected in the areas of rain. Expect VFR flight
conditions and light south-southwest flow outside of thunderstorms
except for a few patches of higher MFR CIGS north of the STL Metro
area. Showers and storms will dissipate within an hour or two
after sunset. VFR conditions are expected until the pre-dawn hours
of Sunday morning when fog will develop. Areal coverage and
density of the fog is not certain at this time, but at least
patchy MFR fog is expected. Fog should dissipate within 2 hours
after sunrise Sunday.

Specifics for KSTL:

Expect showers and thunderstorms to increase in coverage this
afternoon. Timing and intensity is uncertain at Lambert, and there
is a definite chance there could be some intermittent heavy rain
which could reduce the visibility to IFR. However, expect VFR
conditions to prevail for the vast majority of the afternoon.
Showers/storms should dissipate quickly after sunset. With moist
air in place over the STL Metro, think there will be some light
fog at the terminal before sunrise Sunday. Fog should dissipate
within an hour or two after sunrise.





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