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Area forecast discussion 
National Weather Service St Louis MO
339 PM CDT Sat Aug 29 2015

Short term: (through late tonight)
issued at 333 PM CDT Sat Aug 29 2015

Showers have moved out of the County Warning Area for the moment as water vapor
imagery is currently showing that a weak upper low is moving east
across southeast Missouri. There is also a shortwave trough
extending from the Great Lakes into far northeast Missouri and
a vorticity maximum over southwest Missouri that is moving eastward. The
rap shows some weak ascent along the trough axis as it moves east
southeast this evening across northeast Missouri and west central
Illinois while there is also some increased ascent across areas
south of I-70 associated with the vorticity maximum. In addition...the rap
is showing some increase in low level moisture convergence
associated with the vorticity maximum. Will go with a chance of showers and
thunderstorms over the southeastern half of the County Warning Area this
evening...with lessening chances overnight as the moisture
convergence weakens and moves off to the east.


Long term: (sunday through next saturday)
issued at 333 PM CDT Sat Aug 29 2015

(sunday through tuesday)

The upper level trough axis will be slow to move out of the area as
an upper level ridge builds over it across the upper Midwest on
Sunday and Monday. This will keep the upper level trough over the
area at least through Sunday which will supply some lift over the
area through the day. Runs of the cams suggest that convective
coverage will be scattered during the day so have upped probability of precipitation to 30
percent in most areas. GFS and NAM begin to become more uncertain
on location of trough axis by went with dry forecast
though it is possible that the trough axis could well end up in
southern Missouri and bring the southern County Warning Area a slight chance of
thunderstorms. Will also keep Tuesday dry for now...though the NAM
would bring a weak shortwave trough across the area during the day
that may bear watching.

Went on the warm side of guidance through the period as we will be
mixing down air from the 800-850mb layer...particularly on Monday
and Tuesday which has temperatures around +20c which favors
temperatures going back above normal.

(Wednesday through next saturday)

Area will be mainly dry late week into next weekend as upper
ridge axis that extends from the Central Plains into the upper
Midwest on Thursday will shift over Missouri and Illinois by
Saturday. Consequently...surface ridge will linger over Missouri
and Illinois through the medium range period. Temperatures will be
at or slightly above normal as we go into the Holiday weekend as
850mb temperatures remain close to +20c.



Aviation: (for the 18z tafs through 18z Sunday afternoon)
issued at 1222 PM CDT Sat Aug 29 2015

Still expecting widely scattered rain showers/thunderstorms and rain to develop across the region
this afternoon. With the fnt forecast to washout across the
area...timing poss MVFR ceilings and extent of cloud cover will be
difficult. With questions of cloud cover...uncertainty remains
regarding fog development tonight. Have added MVFR visibilities to
uin...but slightly lesser chances exist at cou. Southerly to southwesterly winds
expected again on sun. Low MVFR to possibly IFR ceilings are expected
again tonight. Exactly where the southeastern edge of this cloud deck will
be is difficult to determine...but is currently expected to be
just north/northwest of cou/uin.

Specifics for kstl: widely scattered thunderstorms and rain still expected this afternoon.
Otherwise...expect VFR conditions with southerly to southwesterly winds.



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