Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 092312

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
612 PM CDT Wed Aug 9 2017

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 343 PM CDT Wed Aug 9 2017

A PV anomaly was located over ND and southern SK per early afternoon
water vapor imagery. Model guidance depicts this feature progressing
southeastward towards the Great Lakes and pushing a cold front into
MO/IL tonight and tomorrow. The approach of this system and the
increasing moisture ahead of it will bring increasing cloudiness to
the region as well as isolated to scattered SHRA/TSRA, especially
from very late tonight through tomorrow afternoon.

Overnight lows will likely be a few degrees warmer than last night
due to the increased cloud cover. Highs tomorrow will probably be
similar to what they were today, although the forecast may be a few
degrees too cool if the cloud cover is thinner and/or less
widespread than currently anticipated.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 343 PM CDT Wed Aug 9 2017

Models continue to be in agreement on an active pattern over the
region through Monday. A cold front will approach the area from the
west Thursday night with scattered showers and thunderstorms. There
are timing, strength, and placement differences between models on
how fast the front and shortwave pushes south through the region.
The GFS/ECMWF on agreement with this timing while the NAM is the
outliner with a slower solution. The cold front pushes into north
central Arkansas by late Saturday morning. There are again timing
and placement issues but the front is expected to lift back north
Saturday afternoon/evening north of the Arkansas and Missouri
border. Scattered showers and thunderstorms are possible both
Saturday and Sunday as warm air advection overrides the front
and an upper level disturbance rides along the frontal boundary.

The cold front will finally push just to the south of the region by
late Sunday night. The models diverge on a solution for Monday with
ECMWF dry with high pressure over the region while the GFS has
scattered showers and thunderstorms over the southern 2/3 of the
region. A brief dry period looks probable Tuesday into Wednesday
before another front approaches from the west on Thursday.



.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 606 PM CDT Wed Aug 9 2017

Upper level disturbance will bring an increase in mid level clouds
tonight and tomorrow morning with a chance of showers. Best
coverage of rain will exist from central Missouri (KCOU) to west
central Illinois (KUIN) during the early morning hours with a
downward trend in coverage as it progresses east toward the STL
metro terminals. Wind will remain south/southwest but fairly light
through the period. Can`t rule out some fog impacting KSUS early
tomorrow morning given trends the last few nights, but cloud
cover could inhibit.


VFR conditions will continue with a light south/southwest wind
developing. Chances of showers making it to KSTL look low, but
radar trends will be monitored overnight. Otherwise will see an
increase in mid level cloud cover tonight.





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