Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 181117

Area Forecast Discussion
National Weather Service Sioux Falls SD
617 AM CDT Sun Jun 18 2017

.SHORT TERM...(Today and Tonight)
Issued at 340 AM CDT Sun Jun 18 2017

Cooler air has spread across the area with temperatures in the mid
50s early this morning. This is in response to the strong almost
early fall like wave digging through MN at this time. In the wave of
this wave the area is under a cold pocket of air aloft with
northwest flow from the surface through 100mb. The main focus today
will be the threat for instability showers as it will not take too
much heating to allow for cumulus development. Areas along and east
of about a Brookings to Storm Lake line will see the better threat
for these diurnally driven showers. Weak mid level convergence, a
small ridge of warmer temperatures near the mid level moist layer
and the surface heating will allow for CAPE values around 500 J/kg.
With some minor 20 knot or so shear there may be just enough room
for an updraft to support small hail and brief heavy rainfall. One
reason for a threat for small hail with such minor instability is a
freezing level around 8000-8500 feet AGL. Highs will generally be in
the 70s.

The showers and storms will wane with the loss of heating as will
the cloud cover. With the cool dry air in place lows will fall into
the lower to mid 50s in most locations by early Monday morning.

.LONG TERM...(Monday through Saturday)
Issued at 340 AM CDT Sun Jun 18 2017

The first half of the week will be characterized by a warm up as
upper level ridge works east into the plains.  With a few shortwaves
wrapping around the upper low north of the Great Lakes, could see a
shower or storm in southwest Minnesota or northwest Iowa, but the
limited moisture and instability should keep any activity fairly

Tuesday to be a banner day with low relative humidity and sunny
skies with high pressure in the region.  Surface ridge scoots east
Tuesday night and low level jet develops Tuesday night across the
plains.  This will transport moisture northward, ahead of a series
of disturbances moving along the US/Canadian border.  The second of
these disturbances is expected to intensify, with fairly strong cold
front moving through the region on Thursday.  Interestingly, both
the GFS and EC have developed convection on Wednesday and a strong
cold pool moves into eastern South Dakota on Thursday.  For now,
left temperatures mild ahead of the main front, but trends will have
to be watched on Wednesday into Thursday for the potential for
storms and the lingering effects.

Much cooler and drier conditions are expected across the region next
weekend.  How cool still remains uncertain, but for now the blend is
erring closer to the GFS than the cooler ECMWF.  Either way,
temperatures look to be below normal.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 616 AM CDT Sun Jun 18 2017

Scattered showers and thunderstorms will be possible east of the
James Valley today, with the best chances across southwest MN.
Brief MVFR ceilings will be possible with any stronger storms that
can develop. Outside of the thunderstorms VFR conditions are




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