Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 191113

Area Forecast Discussion
National Weather Service Aberdeen SD
613 AM CDT Sat Aug 19 2017

.SHORT TERM...(Today through Monday Afternoon)
Issued at 403 AM CDT Sat Aug 19 2017

Hi-res models visibility output were spot on with fog this morning
as over the past hour or two it has developed in the Big Sioux
valley across Codington and Hamlin counties. Had inserted this into
the forecast several hours ago and have been making minor changes to
the areal coverage based on the latest satellite trends. KATY is
down to 1/4SM, but by the looks of things, it`s rather localized and
in a small area. Nonetheless, will continue to monitor for possible
expansion and at the very least, may issue an SPS to highlight low
visibility this morning.

Main story for today will be the increasing heat as upper level
ridging moves over the Dakotas. Highs will soar well into the 80s
and 90s, with the warmest conditions across central SD. Breezy
southerly winds will be felt as well. Relative humidity will tank
this afternoon across western and central SD, perhaps below 20
percent for the west river counties. Although, winds appear to stay
below Red Flag criteria. Will have to watch post-frontal winds
across Corson and Dewey counties as they could have some gusts over
25mph. But, areal coverage of humidity below 20 percent across most
of the fire zone seems unlikely. Plus, not overly confident on gusts
over 25mph for extended periods of time - and it would have to be in
the post-frontal environment. Used the HRRR for winds over north
central SD this afternoon which highlights ridges much better.

For the overnight period, will be watching a frontal boundary move
southeast through the CWA. Low-level jet will increase overnight out
ahead of the front, but looks to be strongest over the FSD CWA and
up through the far eastern CWA and into western MN. Expect this area
to have the better precip chances overnight.

The aforementioned frontal boundary looks to stay south of the
region Sunday and Monday, basically hanging out in the Nebraska
region. Although north of this boundary, we will see ripples of
energy in the mid levels moving across the region. This looks to
bring isolated or widely scattered showers and storms off and on
through the period, along with episodes of cloud cover.

.LONG TERM...(Monday Evening through Friday)
Issued at 403 AM CDT Sat Aug 19 2017

The extended will begin with the tail end of a departing shortwave,
followed by a shift to northwest flow aloft for Tuesday/Wednesday
ahead of a building high-amplitude western CONUS ridge. Profiles at
this point are not all that unstable with high pressure moving in
and dry/cool air out of Canada, with just enough low level
instability for some shallow afternoon cumulus. The Canadian airmass
will remain across the area through mid week before the high moves
far enough east to begin return flow. The upper ridge axis will
continue to slowly progress across the forecast area during the
course of the week, and by late work week/weekend timeframe we will
be back into southwest flow aloft and a more unstable environment.


.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
Issued at 612 AM CDT Sat Aug 19 2017

A pocket of IFR fog is mainly impacting KATY this morning. This
will dissipate a few hours after sunrise. VFR conditions are
expected otherwise. We will see some high based showers move
across the area tonight, but uncertainty in timing/coverage
precludes mention in TAFs at this time.




LONG TERM...Connelly
AVIATION...Connelly is the U.S. government's official web portal to all federal, state and local government web resources and services.