Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 131521

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1021 AM CDT Sun Aug 13 2017

Issued at 931 AM CDT Sun Aug 13 2017

High pressure over the Great Lakes will continue to influence
weather conditions over the region today and tonight. Light
southeast winds are expected today and tonight.  Temperatures
will be few degrees warmer today but still below climatological
normals for August.



.SHORT TERM...  (Through Late Tonight)
Issued at 343 AM CDT Sun Aug 13 2017

A high pressure center over the Great Lakes will continue to
influence weather conditions across the area today and tonight.
Initially easterly winds will gradually veer and become
southeasterly today as the high pressure center shifts eastward. The
southerly component to the wind direction should help afternoon high
temperatures rise a few degrees warmer than yesterday. Precipitation
associated with a stalled frontal boundary is expected to remain
south of the area today and tonight. Precipitation associated with a
shortwave moving through the northern plains is expected to remain
north of the LSX CWA through tonight.


.LONG TERM...  (Monday through Saturday)
Issued at 343 AM CDT Sun Aug 13 2017

The synoptic pattern at the start of the long term period will
feature transitioning flow aloft. The persistent trough that had
been in place for the past couple of weeks over the northeastern
CONUS will break down and be replaced by upper-level ridging. This
will allow for the flow over the Midwest to turn to a more active
southwesterly regime by midweek.

The first in a series of PV anomalies will be dropping through the
Upper Midwest on Monday morning. Will have to keep an eye on the
track of a potential MCS likely to develop in response to this
approaching feature, but general indications are that most of this
activity should remain off to the north on Monday leaving the area
mostly dry.

Heights will rise on Tuesday as the upper-level flow turns more to
the southwest. This will allow for a surface front to lift back
north as a warm front, bringing an increase in low-level moisture
and instability to the area. This will result in a few
showers/storms on Tuesday afternoon.  A better chance of
showers/storms will come Tuesday night into Wednesday night, as a
couple of PV anomalies eject out of the southwest flow aloft and
interact with both the retreating warm front, and a cold front which
will pass through sometime on Thursday (timing differs among
guidance). It appears the front will be just close enough to leave
some small chances for showers/storms in on Friday, before
conditions dry out on Saturday as surface ridging builds in.

Temperatures through the period will be on an upward trend. After
highs in the mid 80s on Monday, they will climb into the upper 80s
and low 90s by the middle and end of the week. Heat index values
will also be on the rise as dewpoints increase across the area, with
values expected in the mid/upper 90s to near 100 Wednesday into



.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 626 AM CDT Sun Aug 13 2017

Similar to the last few days, early morning river fog will
dissipate during the first hour or two of the valid TAF period.
VFR conditions are expected thereafter, although additional river
fog may develop at KSUS/KCPS after 14/06z. Initially easterly
winds will gradually veer and become southeasterly around the edge
of a high pressure center located over the Great Lakes.





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