Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 242036
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
336 PM CDT Mon Jul 24 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 333 PM CDT Mon Jul 24 2017

MCV which began in northeast Wyoming early this morning is still
generating an area of showers/thunderstorms moving through the
northern James River Valley late this afternoon. Southern edge of
this precipitation has been diminishing as expected by previous
shift. General consensus of CAMs is to continue tracking the MCV and
associated precipitation eastward, toward west central Minnesota
into the early evening, at most brushing the northern border of our
forecast area with an isolated storm. Increasing low level jet this
evening could reinvigorate this activity across central Minnesota,
and again, tail end of this activity could brush our far northeast
areas during the overnight. But not expecting any more than isolated
coverage. Low level jet will keep southerly winds up overnight, with
lows remaining mild in the mid 60s to mid 70s.

Still seeing scattered high-based cumulus extending well southward,
into south central South Dakota, perhaps indicative of modest low-
mid level moisture return above the surface. This could come into
play as a secondary wave in southwest South Dakota lifts northeast
behind the MCV. CAMs are developing isolated-scattered storms ahead
of this wave in south central South Dakota prior to 00Z, and already
seeing a narrow line of cumulus along a low level boundary extending
from near Philip to Pine Ridge as of 20Z. Cannot rule out isolated
storm development as the wave slides into area with better moisture.
However, boundary is not projected to shift too far east from its
current position, so activity will lose that focus as the boundary
is left behind and upper support lifts off to the northeast. While
an isolated storm or two could work into our far southwest, they are
not expected to survive much beyond sunset.

Shifting focus to Tuesday, primary daytime concern will be a brief
return of heat/humidity. Strong thermal ridge builds northeastward
ahead of a cold front, slated to reach our northwest corner by late
afternoon as 100+kt upper level jet max works across North Dakota.
Driest portions of the forecast area, west of the James River, could
see some triple digit temperatures, with highs expected to range
downward to the upper 80s in our far east. Humidity will also be a
factor, though the far western areas again more likely to mix out
the worst of the humidity, so afternoon heat indices are marginal
for heat advisory. Will let overnight shift reevaluate this. One
area not as likely to mix to full potential would be along the
Highway 14 corridor, which received 2-4" of rain last week. These
areas have remained a little cooler than surrounding locations the
past few days, and anticipate the same tomorrow, so holding highs a
little shy of what full mixing would suggest.

Soundings appear to remain capped ahead of the front, so will keep
late afternoon pops tied close to the boundary, generally northwest
of a Brule-Mitchell-Marshall line by 23Z. Ample instability, but
deep layer shear is lacking with the upper jet positioned so far to
the north. That combined with warm air mass (freezing level above
14kft) will limit hail threat. However, soundings do suggest the
potential for damaging wind, with DCAPE values well in excess of
1000J/kg.


.LONG TERM...(Tuesday night through Monday)
Issued at 333 PM CDT Mon Jul 24 2017

Slow moving cold front is expected to work south and east overnight
Tuesday.  The front is associated with a wave north of the Canadian
border. Veering wind profile is expected ahead of the front, though
the wind speeds are somewhat weak.  Forecast soundings suggest dry
and deep mixed layer, with strong inverted V profile. With veering
shear profile and 0-6 km bulk shear of 30-40 knots along the highway
14 corridor, could get hail to form aloft, but will be a struggle to
get sizable hail to the surface with freezing level above 13K feet
agl. With inverted V extending from the surface to 625-675 mb,
should be a decent potential for storms to produce wind. Have
focused damaging wind mention in the western half of the slight
risk.  Can`t rule out bowing segments further to the south and east,
but believe the greatest potential will be along the slow moving
front.

Severe threat will gradually decrease through the evening hours, but
precipitation coverage is expected to become more widespread through
the morning hours Wednesday.  Precipitation and abundant cloud cover
through the better part of the day should keep highs in the 70s to
lower 80s.

Thereafter, relatively benign pattern is expected as upper level
ridge strengthens across the southern US and retrogrades westward
through the weekend.  This will keep conditions mainly dry with
seasonal highs. With very small standard deviation in the guidance,
did not change temperatures beyond Wednesday. Through collaboration,
removed pops on Sunday morning as pattern is not all that
supportive.


&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1230 PM CDT Mon Jul 24 2017

VFR conditions expected to dominate, with increased southerly flow
creating the primary aviation concern for this period. Occasional
wind gusts exceeding 20-25kt expected through early this evening
in areas west of I-29 corridor. By late evening, increasing low
level jet will result in low level wind shear through shortly
after daybreak Tuesday. Potential for very isolated, high-based
convection affecting far western/northern fringes of the forecast
area through this evening, but chances far too low to mention in
KHON TAF at this time.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...JH
LONG TERM...BT
AVIATION...JH



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