Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 230348

Area Forecast Discussion
National Weather Service Sioux Falls SD
1048 PM CDT Thu Jun 22 2017

.SHORT TERM...(This evening through Friday)
Issued at 251 PM CDT Thu Jun 22 2017

A cold front will continue to move southeastward into
northwest Iowa this afternoon and evening bringing more stable
conditions behind it. Instability and forcing increase after 21Z, as
a weak mid-level shortwave approaches, and PVA increases with height
due to decent upper level support north of the CWA. This will lead
to isolated/scattered thunderstorms along and behind the surface
boundary later this afternoon through late evening. With steep mid-
level lapse rates, and strong 0-6 km bulk shear from 40 to 50 knots,
cannot ruled out a few strong to severe storms. The greatest threat
for severe storms looks to be across northwest Iowa, east of a line
from Sioux City to Cherokee to Spencer, Iowa. If storms develop and
become severe, strong gusty winds up to 65 mph and large hail up to
golf-ball size could be possible.

As the main low moves out of the area tonight, northwesterly winds
will become more dominant, keeping the area mostly dry, but cooler
and breezier than previous days. An upper-level trough will be
moving southward into the Great Lakes, increasing cloud coverage
over the region in the overnight hours through Friday afternoon.
Overall, it will be breezy, with low humidity, and cooler
temperatures. Highs will generally be in the upper 60s north of I-
90, and in the mid to upper 70s south.

.LONG TERM...(Friday night through Thursday)
Issued at 251 PM CDT Thu Jun 22 2017

Highlight of the weekend will be unseasonably cool air mass dropping
into the Upper Midwest. Broad mid-upper trough already in place from
the Dakotas into the Great Lakes to start this period, and a decent
wave drops into the Upper Mississippi Valley late Friday night into
Saturday. This brings a reinforcing cool front into the region on
Saturday, followed by single digit 850mb temperatures. Coldest air
aloft looks to miss us just to the northeast, sliding across central
Minnesota Saturday. If this track holds, it could be just far enough
northeast to save our forecast area from seeing record cold high
temperatures, most of which are in the lower to mid 60s. However, it
could be close for parts of southwest Minnesota, where afternoon
850mb temperatures are coolest. With the upper cold core northeast
of the area, and limited moisture here, better chance of instability
showers or isolated storms should remain northeast of the area as
well. Will carry a slight chance east of the Buffalo Ridge, but dry
conditions with partly-mostly sunny skies elsewhere.

Gradual moderation in temperatures Sunday through the middle part of
next week, as the upper trough slowly shifts east toward New England
and modest upper ridging works into the Northern Plains. Dry weather
should prevail through at least Monday night, as we await moisture
return after surface ridge shifts east into the Mississippi Valley.
Pattern then becomes more unsettled again from late Tuesday through
the end of the week, as various waves slide across the region.
Depending on timing/location of boundaries, could see some 90-degree
readings return to parts of the region by Wednesday or Thursday.
However, too many variables which could impact temperatures as the
convective chances also return, so will not adjust broad blend of
temperatures at this range.

By late next week, models pointing to another trough moving into the
northern Plains/Upper Midwest, bringing another shot of unseasonably
cool air to the region as we move toward July. Still differences in
timing/strength of the trough, so some uncertainty regarding just
how cool, or when the coolest temperatures will impact the region.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1044 PM CDT Thu Jun 22 2017

Primarily VFR conditions are expected through the TAF period.
Northwest winds will increase after daybreak on Friday, with gusts
to 25 or 30 kt possible at times. Additional low end VFR clouds
will increase after 12z Friday morning, spreading southward, but
predominant conditions remain VFR.




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