Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 211751

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1251 PM CDT Wed Jun 21 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 401 AM CDT Wed Jun 21 2017

Early this morning, the upper HIGH in the southwestern CONUS and
upper TROF over the eastern CONUS pattern persists, resulting in NW
flow aloft for our region.  Tropical storm Cindy was churning in the
Gulf of Mexico, just offshore from the Louisiana coast.  At the
surface, a frontal boundary has stalled over northern MO and central
IL, with a light SW flow for most of the forecast area.  Patches of
clouds existed with most locales clear.  There were a few showers
earlier in the overnight period in central MO and southern IL, but
they have either dissipated or moved away, respectively.
Temperatures were in the 70s for most spots with a few pockets of

Recent satellite imagery shows that the old convective line that had
developed on Tuesday has lost its lift over our region, with more
recent lift and cloud development having shifted back north to the
old stalled frontal boundary.  An isolated shower is possible thru
about 14z in parts of central IL near the frontal zone, but

Flow aloft will flatten and weaken today and tonight as Cindy
is anticipated to come onshore in Louisiana around 12z/Thu.  The
surface front over northern MO and central IL will begin to edge
northeastward later this morning accelerate away as a warm front
this afternoon, in part as a response to the backing flow aloft.
This should leave our area upper level disturbance and low level
focus free and dry as a result, however, some discrete hi-res models
are trying to retain some ill-defined boundaries and develop a
shower/storm or two along it this afternoon with little agreement on
location.  With the synoptic boundary long gone, and instability and
moisture not very high, will go dry for this afternoon but place 10%
PoPs over much of the region for this uncertainty.  Dry wx should
continue thru much of tonight, with any pcpn from Cindy expected to
hold off from reaching the southern CWA until after 12z/Thu, and
pcpn that develops along a new cold front to our north should
stay just north of the area as well.

Decent sunshine is again expected today, but wind directions will be
more from the south (180-210) than yesterday.  The big difference is
the much warmer start from 24hrs ago, with temps early this morning
already 5-10 degrees higher.  All in all, should see max temps today
a bit higher than persistence with around 90 for most locations, but
approaching 95 in STL metro.  Min temps tonight will be close to
persistence with little change in airmass expected.


.LONG TERM...  (Thursday through Tuesday)
Issued at 401 AM CDT Wed Jun 21 2017

Showers and storms will move into parts of southeast MO and
southwest IL, south of STL on Thursday as a southerly low level jet
ahead of the remnants of tropical storm Cindy, which will be moving
northward through eastern TX and western LA, brings increasing low
level moisture into this area. Highs on Thursday will be cooler,
especially across southeast MO and southwest IL due to increased
cloud cover limiting solar insolation. Upper level troughing over
the northern Plains and Great Lakes region will send a cold front
southward into our forecast area late Thursday night. Scattered
showers and storms are expected along this front. This will lead to
convection across our entire forecast area late Thursday night and
Friday morning due to this cold front dropping southward through our
area combined with the remnants of tropical storm Cindy along with
its tropical Gulf moisture moving northeastward through AR and
eventually into TN. Most of the showers/storms Friday afternoon will
be across southeast MO and southwest IL, southeast of STL as drier
air begins to advect southward into our region.  The highest pops
and QPF will be across southeast MO and southwest IL on Friday north
of the remnants of Cindy.  Highs will be cooler on Friday due to the
cloud cover, precipitation, and surface winds becoming northwesterly
behind the cold front.  Most of the showers/storms should shift
southeast of the forecast area Friday evening as a surface ridge
builds into our region from the northern Plains. Cooler, slightly
below normal temperatures can be expected Friday night. The ECMWF
model brings another round to convection to our area Saturday night
and Sunday morning as the upper level trough deepens over the Great
Lakes region and a shortwave and reinforcing cold front drop
southeastward through our region.  The GFS model keeps most of the
precipitation north of our forecast area during this time, closer to
the upper level trough.  For now will just include mainly slight
chance pops in the forecast during this time period due to these
model differences. Below normal temperatures can be expected this
weekend into next week due to the persistent northwesterly upper
level flow on the backside of the Great Lakes upper level trough,
and cold air advection behind the initial cold front on Friday, then
again on Sunday behind the secondary cold front.  Temperatures
Sunday and Sunday night will be around 10 degrees below normal.



.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1244 PM CDT Wed Jun 21 2017

A weak quasi-stationary front currently stretches from far
northwest MO into south central IL. This front will retreat back
northward this afternoon, and may be the focus for a few
thunderstorms in IL. Any activity should remain removed from any
of the terminals. VFR flight conditions are expected through the
forecast period with a big surge in cloud cover on Thursday
morning across eastern MO and southwest IL.


VFR flight conditions are expected through the forecast period
with a big surge in cloud cover on Thursday morning.





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