Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 201037

Area Forecast Discussion
National Weather Service Sioux Falls SD
537 AM CDT Thu Jul 20 2017

.SHORT TERM...(Today and Tonight)
Issued at 316 AM CDT Thu Jul 20 2017

The loan severe thunderstorm overnight that produced up to ping pong
ball hail in Windom MN around 1 am is well out of the area with weak
ridging occurring in the wake. Another cluster of storms was across
southwest SD and northwest Nebraska and was slowly drifting
northeast. It appears that some of the activity is likely driven by
an MCV which could help keep activity going into the hours shortly
after sunrise. Soundings in south central SD do show some elevated
1000 J/kg or so CAPE values but shear is pretty minimal so at this
time not anticipating much in the way of severe weather.

As the day moves along troughing should increase across the Western
High Plains which will bring a gradually increasing threat for
thunderstorms to central SD. Capping will play a role in development
so will keep the chances on the low side. As the trough spreads
eastward the low and mid level warm air advection will increase with
elevated instability likely around 1500 J/kg but pretty weak low and
mid level shear. This will lead towards an isolated severe
thunderstorm threat but potentially a more widespread shower and
thunderstorm scenario. Will keep pops around 50 to 60 percent during
the overnight hours.

As for temperatures backed off a bit across parts of SD and MN as
easterly flow will keep mixing down a bit. There will also be a
threat for some additional cloud cover, so will aim for mid 80s to
around 90. Along the Missouri River into parts of northwest IA
temperatures and humidity will still be higher so plan on keeping
the small heat advisory around Sioux City.

.LONG TERM...(Friday through Wednesday)
Issued at 316 AM CDT Thu Jul 20 2017

Muggy conditions continue into Friday as elevated mixed layer keep
the near surface layer capped through much of the day. As a short
wave moves across the area on Friday, could see storms try to
develop Friday evening.  Models still indicate 75-125 surface based
cin Friday night, so there is some question as to whether anything
would develop in the first place. Ample shear mainly concentrated
along and north of I-90 may lead to a few marginally severe storms.
Will likely need to consider a heat advisory for southern zones on
Friday with highs in the mid 90s and dew points well into the 70s.

Northwest flow develops Friday night but remains quite mild
throughout the day on Saturday.  Drier air filters into the region
from the north, so will likely not need any headlines on Saturday
despite highs in the 90s.

Cooler air works into the region early Sunday morning as a backdoor
cold front slides south across the region. The cooler and drier
conditions will continue into Monday, before a series of shortwaves
track through the region Tuesday into Wednesday next week.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 536 AM CDT Thu Jul 20 2017

Patchy MVFR fog will be possible along highway 14 into parts of
southwest MN through about 14z this morning. Isolated
thunderstorms will be possible in central SD with scattered
thunderstorms possible over the entire area tonight into Friday
morning. Outside of the early morning fog and thunderstorm chances,
VFR conditions are expected.


IA...Heat Advisory from 1 PM this afternoon to 8 PM CDT this evening
     for IAZ031-032.

NE...Heat Advisory from 1 PM this afternoon to 8 PM CDT this evening
     for NEZ013-014.



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