Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 212322
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
622 PM CDT SAT MAY 21 2016

.SHORT TERM...(This evening through Monday afternoon)
Issued at 245 PM CDT Sat May 21 2016

A few lingering showers are rapidly dissipating this afternoon,
and despite the rather breezy conditions, Saturday is turning out
to be very pleasant. These pleasant conditions will continue into
the overnight hours, with the main focus of the forecast on the
severe weather risks late Sunday and Monday.

Tonight: Upper troughing over the Rockies will continue to keep
moisture transport pushing northwest into western Nebraska and the
western Dakotas overnight. We`ll again see a return of low level
stratus into central SD/NE tonight, and as the LLJ begins to veer
after midnight, this stratus will begin to advect into the Missouri
River valley. Further east, winds will gradually settle, but remain
elevated enough to keep temperatures in the lower 50s.

Sunday:  The slow and gradual advection of quality sfc moisture will
continue through the day, with moisture trying to pool ahead of an
eastward advancing frontal boundary nosing into the western
Dakotas/Nebraska by afternoon.  Soundings continue to both a
continuation of stratus west of the James river into the afternoon,
but also the arrival of an capping inversion around 750mb. As mid-
lvl energy begins to edge into the Plains should see an erosion of
this stratus ahead of the boundary, allowing an area of MLCAPE
approaching 2000-2500 J/KG by late afternoon. While effective
shear is marginal (25-35 KTS), CAMS suggest relatively discrete
cells forming ahead of the frontal boundary along a line near
Pierre to Valentine late in the afternoon.

Sunday night: Given the marginal shear profiles, the discrete nature
of the activity should be limited with storm interactions and cold
pool development allowing for several clusters of storms to form as
they try to push east towards the Missouri River valley. Further
east towards Mitchell and Yankton, soundings continue hold onto
capping inversion until the LLJ develops later in the evening.
The main risks continue to be focused on damaging winds with some
potential for hail in the initial stages of convection. DCAPE
values to push 1000 J/KG during the evening, and with mid-lvl dry
air, would feel potential for marginally severe winds. Hail
potential should be limited by the lack of effective shear. The
fairly unidirectional flow aloft should promote a slow eastward
progression to storms through the night. CIPS analogs continue to
support the idea of isolated to scattered severe weather reports
Sunday evening and early Sunday night, but that severe weather
risk will greatly diminish eastward with time.

Monday: With no strong push eastward of the storms, and rather weak
frontal boundary , rain may linger well through the day on Monday
over the eastern half of the CWA. Temperatures behind this cloud
shield may climb back into the 80s.  Very uncertain chance for
redevelopment of convection Monday afternoon remains with the main
concerns focused on forcing.

.LONG TERM...(Monday evening through Saturday)
Issued at 245 PM CDT Sat May 21 2016

Looks like unsettled weather pattern will continue throughout the
week with upper level flow becoming more southwesterly increasing
the shear a little, especially on Tuesday.  Will have to keep on
Tuesday as we may have a little sleeper severe weather event, but
confidence remains low at this point.  Very muddied pattern so was
very difficult to pin down exact timing of precip events.  Looking
ahead at Holiday weekend looks to be even more unsettled as models
bring a pretty strong short wave over the area keeping a pretty good
chance for storms beginning on Thursday and continuing through
Saturday.

Highs look to be in the 70s throughout the extended period, but will
be heavily influenced by the cloud cover throughout the period.
However, having said that I think the surface flow should allow
temps to warm to seasonal normals.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 622 PM CDT Sat May 21 2016

Primary concern in the TAFs is the development of low level wind
shear late tonight into early Sunday morning. A strong low level
jet is expected to develop over central South Dakota early tonight
and move eastward through the night. With wind speeds around 1500
ft AGL from 40 to 45 kts and surface winds around 10 kts...low
level wind shear will first develop around Huron around 06Z and
the affect Sioux Falls and Sioux City late tonight. Winds will
rapidly increase at the surface early Sunday morning ending the
wind shear threat although gusts to 30 kts can be expected through
the afternoon. There will also be a brief period of MVFR ceilings
on Sunday morning around Huron. These clouds should lift as the
surface warms through the morning. Outside of that time, VFR
conditions are expected through the period. After 00Z, expect
thunderstorms to approach Huron and move toward Sioux Falls and
Sioux City at or even after 06z.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Dux
LONG TERM...Heitkamp
AVIATION...Schumacher



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