Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 211112

Area Forecast Discussion
National Weather Service Sioux Falls SD
612 AM CDT Sat Oct 21 2017

.SHORT TERM...(Today and Tonight)
Issued at 334 AM CDT Sat Oct 21 2017

A shortwave is presently analyzed lifting out of eastern KS very
early this morning with thunderstorms developing through the eastern
Nebraska as theta e advection lifts northward. Some of this activity
may graze our southeastern IA zones through the early morning.
Otherwise, the cold front which will sweep across our area during
the day is presently still located over west central SD. The
boundary should be pushing into our western zones by 12Z. Models
have sped up the progression of the front slightly, and it will be
located along the I-29 corridor by 18Z, then be exiting our eastern
zones by around 22Z. The greater rain chances remain from the I-29
corridor and eastward during the afternoon where instability will be
optimized. There is still some uncertainty on how unstable we
become, dependent on coverage/timing of morning convection over that
area and how quickly the front progresses to the east. Models still
progging a brief period of MU CAPE around 1000 J/KG just ahead of
the front in the afternoon before it quickly pushes to the east. The
best 0-6 km shear continues to be right along the front, so the
greater severe threat would be with the boundary, though again it is
very conditional based on the factors mentioned above, and primarily
affecting our southeastern most IA counties in the mid to late
afternoon. DCAPE values look to be pretty weak, so think the primary
threat would be large hail. There is fairly strong cold air
advection behind the front, so temperatures will steady out or fall
slightly with the passage of the system. High temperatures will be
around 60 through south central SD and the James River Valley, with
upper 60s east of I-29, before falling into the lower 60s by
afternoon. It will be another breezy day with the cold air advection
and enhanced mixing behind the front, as winds turn from southerly
to northwesterly.

By tonight the front will be east of our area, with clearing skies
and dying winds as weak high pressure builds into the region. This,
in conjunction with the caa will be optimal for colder temperatures,
and looking at lows in the mid 30s to around 40.

.LONG TERM...(Sunday through Friday)
Issued at 334 AM CDT Sat Oct 21 2017

The high slides quickly to the east by Sunday with a southerly flow
returning to the region. With that, highs will climb back into the
60s, nearing 70 over south central SD. Another frontal boundary
pushes across the area on Sunday night, with little fanfare other
than bringing gusty northwesterly winds on Monday with highs again
in the 60s. An upper level trough deepens over the central CONUS on
Monday night and Tuesday, and it will be a much cooler day on
Tuesday with highs only lower to mid 50s.

Up and down temperatures will be the theme for the remainder of the
week in an active upper level pattern. After a warm up on Wednesday,
cooler air filters back into the region for the end of the week as
an upper level trough settles into the central/eastern portions of
the Nation, though models are differing in how this evolves. As a
result, there is some uncertainty for that period. Because of that,
confidence in precipitation chances are low, though there are some
trends toward a better chance around next weekend.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 611 AM CDT Sat Oct 21 2017

Beginning to see scattered showers develop this morning ahead of a
frontal boundary quickly pushing eastward. MVFR ceilings expected
ahead of this boundary through the morning, quickly pushing east
as the boundary moves through. Winds will turn gusty from the west
to northwest as the front passes.

Skies will clear by the late day to evening hours with VFR
conditions overnight.




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