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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
609 am CDT Friday Jul 31 2015

Short term...(today and tonight)
issued at 348 am CDT Friday Jul 31 2015

Isolated thunderstorms associated with an axis of instability
south of the Missouri River early this morning are expected to
continue to move southward into Nebraska and Iowa this morning.
This will leave mostly sunny skies for the area through the day.
With a ridge of high pressure over the eastern plains...winds are
expected to be light. But a strong July sun is expected to allow
enough mixing for temperatures to be as warm or a couple of
degrees warmer than yesterday...from the middle 80s to lower 90s. In
addition...with dry air just above the surface...dew points will
again fall into the lower to middle 50s this afternoon with upper 40s
possible in parts of SW Minnesota.

Overnight...with the steep lapse rates...low level warm advection
and middle level front again south and west of the Missouri
River...expect dry weather to continue over the area. As the high
pressure slowly move east overnight winds will gradually shift to
southeast but remain fairly light. As a result...with radiational
cooling...especially along and east of the Big Sioux River...lows
should fall into the upper 50s over southwest Minnesota and adjacent
areas of northwest Iowa and southeast South Dakota...with lower 60s
elsewhere.

Long term...(saturday through thursday)
issued at 348 am CDT Friday Jul 31 2015

On Saturday a shortwave begins to drop southward on a northwesterly
upper level flow. Out ahead of the feature will have increasing 850
mb Theta-E advection across the area during the day as a low/middle level
warm front lifts through the region. While there will be weak
capping across the area through much of the day...think that as
the shortwave moves into the area in the afternoon and middle/upper
level temperatures cool that the cap will be broken. This will
allow for potential thunderstorm development by late afternoon and
evening...focused more in the south and east where low level
convergence will be optimized. MUCAPE values by afternoon will
average around 1500 j/kg with decent speed/directional shear and
effective shear values running in excess of 40 kts. As a
result...severe storms will be possible with the main threats
being damaging winds and large hail. It will be a very warm day
with highs middle 80s to lower 90s.

Thunderstorms will pull eastward on Saturday night...and Sunday
looks dry in spite of a secondary shortwave/front dropping through
the region with little moisture to work with. Temperatures will be
even warmer on Sunday...topping out in the upper 80s east to the middle
90s through south central South Dakota. Somewhat cooler air then
feeds in behind this system with highs on Monday dropping to lower
to middle 80s.

For the remainder of the extended models point toward a gradual
cooling trend through next week...with highs by Thursday and Friday
only in the 70s as an upper level low remains anchored over eastern
Canada. There does appear to be periodic rain chances through the
period with various shortwaves traversing the northwesterly upper
level flow...though exact timing hard to pin down with usual model
differences in the extended.

&&

Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 608 am CDT Friday Jul 31 2015

VFR conditions expected through 12z satudray. Any thunderstorms
that develop from southwest South Dakota into Nebraska and western
Iowa are expected to stay south of Sioux City through the period.
Also there is a low probability of IFR fog toward 12z Saturday in
Sioux City but did not include at this time as strong mixing
this afternoon should keep moisture shallow Friday night and
prevent fog from developing

&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

Short term...schumacher
long term...jm
aviation...schumacher

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