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National Weather Service Sioux Falls South Dakota
1054 PM CDT Friday Aug 29 2014

Short term...(this evening through saturday)
issued at 321 PM CDT Friday Aug 29 2014

Atmosphere destabilized enough this afternoon as temperatures warmed above
70 degrees. Instability was enough for thunderstorms to form and
there was enough vorticity stretching in the 0 to 3 km column to
cause brief funnels to form mainly along and east of I-29. Had a
few reports of such funnels and issued a Special Weather Statement
to cover the possibility. The threat for more funnel clouds will
not linger much into the late afternoon hours.

As main front moves east...so GOES the storm chances and also as
dusk nears...storms will also begin to weaken and dissipate. Short
term hi-res models all point to storms weakening and pulling off to
the east by 06z.

Not much going on after that as wave rotates through and subsidence
begins to influence the weather. May have areas of fog tonight in
areas of southwest Minnesota...but should not be dense at all.
Otherwise Saturday...looks a lot brighter with more sunshine after
morning clouds & fog burn off. High temperatures will be a little warmer
with the sunshine but still not going much above 80 degrees.

Long term...(saturday night through friday)
issued at 321 PM CDT Friday Aug 29 2014

Saturday night into Sunday morning will likely see a broken line of
showers and thunderstorms move from west to east. A lead piece of
energy will move through North Dakota spreading fairly strong low to
middle level warm advection across the area. The instability in the middle
levels on the moderate level so not out of the question for some
isolated severe thunderstorms. The best chances likely north of
Interstate 90.

Sunday into Sunday evening still a very good set up for severe
thunderstorms. Some morning elevated storms likely but expected to
weaken or dissipate...allowing for some sunshine and
destabilization. The latest models have come in a bit warmer in the
middle levels which could suggest a stronger cap and smaller chance for
thunderstorm development but with virtually all models producing
thunderstorms and such a strong wave moving into the area will
continue higher probability of precipitation and continue to hit the severe weather threat
fairly hard. The deep layer shear is very good...not great but with
convective available potential energy likely around 2500 j/kg organized severe thunderstorms are
somewhat likely as well as a decent potential for discrete cells.

In the outer periods (tuesday through friday)...weak ridging will
move through Tuesday night into Wednesday with little if any chance
for showers and thunderstorms at this time. This is in response to a
deepening low pressure over the western United States. Fast
northwest flow will remain in place along the U.S. Canadian border
which will necessitate some smaller probability of precipitation Wednesday into Friday over
parts of the area. The strongest piece of energy is forecast to move
across Thursday night into Friday and will keep the highest probability of precipitation in
during this time. Otherwise fairly warm during this time with highs
mainly in the upper 70s to middle 80s.

&&

Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1054 PM CDT Friday Aug 29 2014

06z tafs will likely reflect southward moving stratus moving in
from north of our forecast area. Northeast South Dakota and eastern ND has
quite a bit of MVFR ceilings...and with northerly low level
winds...the stratus will more than likely advect southward. The
latest NAM has a good reflection on this...so based the ceilings
on timing from the 00z NAM model. Fairly confident that khon and
kfsd will receive MVFR stratus...but because of this...and coupled
with a northerly wind flow...much of the potential fog formation
may be held at Bay. Ksux is a different story. The NAM does not
bring the stratus far enough southward to affect Sioux City. If
this happens...then believe that ksux has a better chance than
kfsd and khon of receiving fog. So kept some IFR mention of fog
going for that location near sunrise. Noticed that techameh
Nebraska to the south is already just over a mile in visibility.
The stratus should advect out...and also mix out of our area by
middle to late morning on Saturday with VFR conditions to follow.

&&

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

$$

Short term...heitkamp
long term...08
aviation...mj

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