Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 201645

Area Forecast Discussion
National Weather Service Sioux Falls SD
1145 AM CDT Fri Oct 20 2017

.SHORT TERM...(Today and Tonight)
Issued at 302 AM CDT Fri Oct 20 2017

It will be another very mild day across the area in a strong
southerly flow with high pressure to our east and an approaching
trough to our west. With the tight gradient and winds at the top of
the mixed layer running close to 40 kts, it will be a windy day. At
this point, think that wind speeds will remain just below advisory
criteria, but will be something to keep an eye on throughout the
day. High temperatures will again run mid to upper 70s.

By tonight an upper level trough over the western CONUS begins to
nudge eastward, as a surface cold front slides into the western
portions of our CWA. Instability begins to increase out ahead of the
system later at night, and may see showers and thunderstorms develop
mainly from the I-29 corridor and eastward after midnight. It will
remain breezy overnight, and lows will be mild - in the upper 50s to
lower 60s.

.LONG TERM...(Saturday through Thursday)
Issued at 302 AM CDT Fri Oct 20 2017

The frontal boundary slides across the area on Saturday, with
showers and thunderstorms likely east of the James River Valley.
There is enough instability and shear that an isolated severe storm
cannot be ruled out in our very far eastern IA zones, though with
the front clearing our area by afternoon, the greater risk lies to
the east of our CWA. If the frontal timing were to slow a little bit,
then the risk over our area would be greater. With clouds, showers,
and cold air advection behind the front, it will be a cooler day
with highs lower 60s west to around 70 east of I-29.

With the passage of the upper level trough, a nearly zonal flow sets
up for Sunday, before upper level energy dives southward into the
central CONUS on Monday and Tuesday, carving out a trough over the
eastern U.S. by midweek. Another cold front pushes across the region
on Monday, though rain chances are on the low side with weak
forcing. This will bring much cooler air for Tuesday with highs back
into the 50s. Roller coaster temperatures will be the theme for the
middle and end of next week, with some recovery on Wednesday,
followed by another cool down on Thursday and Friday in a rather
active upper level upper level pattern. Even so, rain chances look
minimal through the period.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1143 AM CDT Fri Oct 20 2017

VFR through the evening and much of the overnight. Rain, scattered
thunderstorms and MVFR ceilings will become more likely very late
tonight into Saturday morning. The better chances for rain,
thunderstorms and MVFR ceilings will be east of the James River.




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