Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 201744

Area Forecast Discussion
National Weather Service Sioux Falls SD
1244 PM CDT Tue Jun 20 2017

.SHORT TERM...(Today and Tonight)
Issued at 341 AM CDT Tue Jun 20 2017

A weak wave moving through a fairly strong northwest oriented upper
level jet will bring a very small chance for showers to areas east
of the Buffalo Ridge in southwest MN early this morning. After this
small threat passes an extremely nice day is in store as high
pressure settles in at the surface. The low level thermal field is
similar to Monday so highs likely to be similar as well. Readings
could come in a couple degrees cooler if the 10-15 kft cloud deck
this afternoon expected from about the James Valley east to around I-
29 is a little thicker.

As the high pressure shifts east southerly flow at the surface will
develop along and west of Interstate 29 overnight. Aloft the flow
will turn a bit more southwest with some marginal instability
shifting north. This will bring a small threat for what appears to
be non severe thunderstorms to areas west of Interstate 29 after

.LONG TERM...(Wednesday through Monday)
Issued at 341 AM CDT Tue Jun 20 2017

Wednesday looks to be a fairly active day across the area. On
Wednesday morning there is a warm front lifting north across the
area that may result in scattered thunderstorms mainly north of I-
90.  These storms are virtually uncapped when lifting from 850-800
mb, with 500-1000 J/kg of elevated CAPE. Environmental lapse rates
are nearly moist adiabatic, and with effective shear being fairly
limited, expect storms to remain non-severe. Skies are expected to
clear throughout the day with strong heating throughout the daytime
hours ahead of an approaching cold front.  With strong southerly
flow ahead of the front, and expecting strong moisture transport
into the area, but still may not be enough to break the cap.  Models
suggest temperatures would need to climb into the lower 90s with dew
points approaching 70 to have a chance at breaking the cap. 00Z NAM
Nest suggests the potential of the cap breaking near 21z near
Beresford. NAM soundings suggest fairly strong cap with cin over 100
just up the road in Sioux Falls at that time, so think it will
likely wait till late in the day at the earliest.  At this time,
there may be a very weak short wave along the Nebraska/South Dakota
border helping to weaken the cap and trigger convection.  If
convection can develop, agree with SPC analysis focusing on large
hail and damaging winds. Could also see a tornado or two if there
are lingering boundaries left over from the morning convection.

Cooler air pours into the region on Thursday and continues into the
weekend as a series of fronts parade through the area.  With this,
could see periodic rounds of precipitation, especially on Saturday
ahead of a strong shortwave moving through the area.  With 850 hpa
temps tumbling towards 0 C on Saturday night into Sunday morning,
temperatures will struggle to reach 70 F for highs on Saturday.

Warmer conditions will develop Monday into Tuesday as upper level
jet re-establishes back to the north.  As the open shortwave across
our area on Saturday wraps up late in the weekend across the Great
Lakes region, could see additional chances for light
showers/thunderstorms as short waves wrap into the region in the
cyclonic flow.  Not much in the way of model agreement on these
specific features, so left the blend as is for time being.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1225 PM CDT Tue Jun 20 2017

VFR conditions will prevail through the TAF period. Isolated
thunderstorms may develop tonight after 06Z from west to east, but
at this time confidence is low to mention it in the TAF.




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