Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 271158

658 AM CDT Sat Jun 27 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 310 AM CDT Sat Jun 27 2015

Have added slight chance for thunderstorms this afternoon based on
that there was upstream convection today, and forecast soundings
show that atmosphere will become unstable again today.  Both the NAM
and GFS show a upper shortwave trough moving across the area during
the midday hours with the GFS developing some QPF over the area
during the afternoon.  Even the HRRR supports this idea with it
breaking out isolated convection during the afternoon over most of
the CWA.  This convection will die out quickly this evening with the
loss of daytime heating.  Temperatures today will remain below
normal even with mixing up to 850mb.

.LONG TERM: (Sunday through Friday)
Issued at 310 AM CDT Sat Jun 27 2015

(Sunday and Monday)

A second, stronger trough will drop down in northwest upper flow on
Sunday night.  There will be additional thunderstorms develop ahead
of it on Sunday as the atmosphere becomes unstable with MLCAPES in
the 1000-2000 J/kg range. A few isolated severe thunderstorms should
be possible over the area Sunday into Sunday evening and deep layer
shear of around 40kts. The trough will move off to the southeast
by Monday, though the atmosphere will still be unstable behind the
front today. Will keep a slight chance of showers and thunderstorms
over part of the forecast area on Monday.

Temperatures these two days look slightly warmer as mixing will be
up into the 800-850mb range.

(Tuesday through Friday)

Upper pattern will remain amplified during this period with large
upper high in the western CONUS and mean trough in the east.   This
will keep a meandering frontal boundary close to our area during
mid-late week.  Temperatures will remain below normal.



.AVIATION:  (For the 12z TAFs through 12z Sunday Morning)
Issued at 638 AM CDT Sat Jun 27 2015

Fog will dissipate in UIN later this morning, while the MVFR
stratus deck in COU and the St Louis metro area advects south of
this area. There will be scattered to broken diurnal cumulus
clouds developing across the area late this morning and afternoon
with isolated afternoon showers/storms possible. The diurnal
cumulus clouds will dissipate early this evening. The northerly
surface winds will become light early this evening as the surface
low over western OH moves further east and the surface ridge over
the Plains moves southeastward through our area.

Specifics for KSTL: The MVFR stratus cloud deck will advect south
of STL later this morning. Scattered to broken diurnal cumulus
clouds will develop late this morning and afternoon. There may be
isolated showers and storms this afternoon, but will leave out of
the STL TAF for now due to sparse coverage expected. The cumulus
clouds should dissipate early this evening due to the loss of
daytime heating. The northerly surface wind will become light
early this evening, then become southwesterly by late Sunday
morning as the surface ridge shifts southeast of STL and a cold
front approaches.





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