Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 212257

Area Forecast Discussion
National Weather Service Sioux Falls SD
557 PM CDT Mon Aug 21 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 242 PM CDT Mon Aug 21 2017

Continuing to watch a potent MCS tracking east southeast across far
southeast SD into southwest MN, northeast NE, and northwest Iowa
through the evening ahead of an advancing frontal boundary. The main
threat remains locally heavy rainfall, along with a severe threat
south of I-90 where sunshine has been more prevalent and
dewpoints have surged into the upper 60s and lower 70s. The strong
forcing associate with the wave, good instability, and strong
shear will continue to bring a severe threat in northwest Iowa,
with large hail and wind gusts to 70 mph possible in the main
thunderstorm complex, as well as any convection that may form
ahead of the MCS. Some spotty additional non severe convection
will also be possible this afternoon and evening in the wake of
the MCS along the elevated front. Rainfall rates will remain quite
hefty, with many locations seeing 1 to 2 inches of rainfall in a
short amount of time. With the forward advancing nature of these
storms, flash flooding should be very isolated and mainly of
concern in urban areas, so will hold off issuing any flood watch

With the system exiting to the east late this evening, skies will
quickly clear behind the rain from northwest to southeast. High
pressure will expand across the region late tonight into Tuesday,
which will lead to a rather pleasant day with relatively light
winds, mild temperatures in the 70s, and sunny skies.

.LONG TERM...(Tuesday night through Monday)
Issued at 242 PM CDT Mon Aug 21 2017

Due to ongoing severe weather, did not make any alterations to the
mid and long range forecast grids.

Upper level northwest flow regime will continue to dominate the
weather pattern moving into the later half of the week, with
ridging to our west gradually shifting eastward across the
Intermountain West. Within this pattern, we may see a few minor
shortwaves drop across the northern Plains, however models not
showing a great deal of agreement, nor much intensity in these
waves. Pops will remain minimal through Thursday. Temperatures
look near seasonal, in the 70s to lower 80s.

Models in better agreement with bringing a wave through the region
around the Thursday night into Friday time frame, with a trailing,
and slightly more potent trough moving into the northern Plains
Friday night and Saturday.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 553 PM CDT Mon Aug 21 2017

Showers and thunderstorms will continue to pull through the lower
MO River Valley into northwest IA during the early evening.
Otherwise, clouds will decrease with VFR conditions expected
through the TAF period.




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