Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 152345

Area Forecast Discussion
National Weather Service Sioux Falls SD
645 PM CDT Sat Jul 15 2017

.SHORT TERM...(This evening through Sunday)
Issued at 358 PM CDT Sat Jul 15 2017

Another hot and humid day across the region thanks to pooling
boundary layer moisture and temperatures now surging into the 90s in
some locations.  A frontal boundary has stalled a bit across the CWA
early this afternoon, expected to get another push southward by the
early evening hours.  Heat index values have locally jumped to or
just above 100 degrees.  Evening conditions with the light winds and
very slow cool-off will remain quite muggy.

Slightly drier air will try to sink southwest into the region
overnight, and may allow temperatures in the northeastern CWA to
cool near 60 degrees.  The warmest overnight lows will be found near
the Missouri River where temperatures may bottom out near 70.

High pressure moving across the Great Lakes on Sunday will keep
surface winds from the southeast over much of the area and dry
conditions in place. The aforementioned front will pivot back
northward stalling just outside the western boundaries of the CWA.
Temperatures should remain slightly cooler than today, with lower
80s over the Buffalo Ridge to the middle and upper 90s over the
Missouri River Valley. The southeast wind fetch will transport a bit
more moisture back into the area through the day.

.LONG TERM...(Sunday night through Saturday)
Issued at 358 PM CDT Sat Jul 15 2017

Sunday night should find an increasing south to southeast wind flow
along with maintenance of low-level moisture. Enough gradient to
think that any widespread fog would be unlikely, but moist enough
below inversion that would not be surprised by a few low-lying spots
getting a bit murky with temps bottoming out only in the mid 60s to
around 70.

By Monday, the closed low which is currently residing across the
central high plains will begin to open up a bit and shear along the
southern edge of the westerlies running along the northern tier as
the ridge aloft breaks down.  Monday should primarily be dry, and
only an outside chance for lift with either tail of northern stream
wave or the weakening upper low to the south to bring a minimal late
day chance for thunderstorms.  Otherwise, more breezy warm and humid
conditions, with a few more clouds, and temperatures in the 90s,
except where a few readings exceed the century mark toward south
central SD.  GFS continues to suffer the overheated bias which has
plagued it for several years at this time, especially with the 40-
44C 925 hPa temps on Tuesday!

The truth on Monday night probably lies somewhere between the GFS
bullish precipitation, and the more minimalistic view of the ECMWF.
Weak jet streak moving past later in the night likely to bring a
better dynamic support for small MCS toward northern CWA and
especially veering toward SW MN later in the night and Tuesday
morning with diverting low-level jet and on gradient of the better
mixed-layer aloft.  Gradually, boundary will progress southward
through the CWA, with extent largely at odds with the degree of late
night and early morning convection. Have hedged bets with mainly
upper 80s southwest MN to mid 90s Missouri river valley. With most
solutions indicating some degree of minor ridge recovery and
continued influx of warming temperatures aloft, would think that
there would be diminishing threat for convection going through
Tuesday night.

Mid to late week solutions revolve around broad flat ridging,
placing the area on the edge of the westerlies, the edge of the
warmest temperatures, and keeping proximity of the lower- to mid-
level boundary. Pattern is actually fairly favorable to develop a
larger MCS in the region around Wednesday night as another jet
impulse puts area into a broad right entrance region.  As mean ridge
axis works to retrograde back through the Rockies by Thursday, a
reduction of rain chances again before potential for next
disturbance of monsoonal origin rides the ridge back into the region
around Friday night. Temperatures mainly will remain on the warmer
side of normal, unless larger scale MCS has something to say
regarding clouds and precipitation.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 639 PM CDT Sat Jul 15 2017

VFR conditions are expected through the TAF period.




LONG TERM...Chapman
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