Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 192315

Area Forecast Discussion
National Weather Service Sioux Falls SD
615 PM CDT FRI AUG 19 2016

.SHORT TERM...(This evening through Saturday)
Issued at 358 PM CDT Fri Aug 19 2016

Very light rain continues develop on the trailing edge of a
departing MCV that moved into western Minnesota earlier today.  Will
continue to watch elevated convection form over the extreme
southeastern portions of the CWA, from Sioux City to Spencer and
areas southeast.  High-resolution HRRR guidance seems to be handling
this convection well with these scattered thunderstorms sliding east
of the region early this evening. There remains upwards of 1000 J/KG
MLCAPE in the region and with effective shear approaching 30 knots,
a few low-topped supercells couldn`t be ruled out.

Further west, a large area of rain associated with a larger upper
trough digging into the Western Dakotas will bring a large area of
showers with very isolated embedded thunder eastward overnight. As
this trough pivots through the CWA rain will spread into areas east
of I-29 after daybreak.

Saturday will be plagued with plenty of cloud cover, blustery
northwest winds, and temperatures struggling to reach 70 degrees.
Depending on if we can see any breaks in the cloud cover, several
models continue to hint at redevelopment of showers and isolated
thunderstorms after noon especially along the Buffalo Ridge. With
steep low-lvl lapse rates and 50 to 100 J/KG MLCAPE will include
thunderstorm wording in the forecast.

.LONG TERM...(Saturday night through Friday)
Issued at 358 PM CDT Fri Aug 19 2016

Saturday night looks dry and cool as chilly high pressure takes hold
across the region. With clear skies and light winds, it looks like a
good night to go below consensus guidance readings for the favored
locations in low terrain. Sunday looks very pleasant at this time
with light winds continuing and pleasant highs ranging mostly in the
mid 70s to lower 80s. Then by Sunday night, the high pressure system
will be east of our forecast area which will bring a return flow to
the region.  Although the flow is not strong enough, it will likely
be enough to moderate temperatures a little warmer then consensus
low temperature values.  Therefore threw out the coldest guidance
members and came up with mid 50s around Spencer Iowa, to the lower
60s in the Chamberlain vicinity.

Monday and Tuesday will follow with definite windy conditions from
the south, as an upper trough of low pressure begins to deepen in
the Pacific northwest. Looks very likely that wind speeds will
average a stout 20 to 35 mph which will warm up temperatures and
increase dew points once again. Therefore trended toward the warmer
guidance values on Monday such as the RAW model values, but the
blended values Monday night were not altered as they look warm
enough already. Tuesday will have similar highs as Monday with a lot
of lower to mid 80s in our east, to lower 90s toward central SD.

The next element to watch is another fairly significant cold frontal
passage after the warmth on Tuesday. The usual timing discrepancies
exist between the deterministic ECMWF and GFS are there, with the
GFS about 6 to 8 hours faster with the frontal passage when compared
to the ECMWF. At this time, blended the two solutions. and there
will be a decent chance for showers and thunderstorms mainly east of
the James River valley Tuesday night and early Wednesday. Behind
this front, cooler weather will filter in, giving highs only in the
70s by next Thursday and Friday.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 611 PM CDT Fri Aug 19 2016

Showers and isolated thunderstorms are expected to spread back
over the area overnight. There could be some local mvfr ceilings
with the showers at times. These showers will then end from the
west on Saturday. Northwest winds will gust to near 20 kts on
Saturday afternoon.


.FSD Watches/Warnings/Advisories...


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