Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 150806

Area Forecast Discussion
National Weather Service Sioux Falls SD
306 AM CDT Sat Jul 15 2017

.SHORT TERM...(Today and Tonight)
Issued at 304 AM CDT Sat Jul 15 2017

Main story today will be how hot will we get?  A couple of things
will have an impact on today`s highs.  The first one is the cloud
debris left over from overnight storms across northern sections of
South Dakota.  Scattered storms developed in response to a weak
short wave passing through. Satellite shows storms dying quickly
with warming cloud tops and with upper level flow, most of the Tri
State area will experience the cloud debris from the storms.
However, by noon, most of cloudiness will be to the east. Morning
clouds will temper a rapid rise in temps, but as clouds clear
mercury levels will be on the increase. Second thing that will
influence temperatures will be a relatively weak cold front that is
forecast to set up over portions of the forecast area. Main effect
of the front will be whether or not to go with a heat advisory
for portions of the southcentral. At this time, decided not to
issue advisory as heat indices are borderline and the worst of the
conditions should only be an hour or two. But day shift will have
to obviously keep an eye on temps and how quickly they rise. No
matter what though, it`ll be hot.

Tonight will be pretty tranquil other than a few thin high clouds
overhead.  Temps will fall a few degrees more than recent nights due
to slightly cooler air coming in behind the front.

.LONG TERM...(Sunday through Friday)
Issued at 304 AM CDT Sat Jul 15 2017

Upper ridge remains dominant across the region into Sunday, but
temperatures should be a little cooler than today, especially in
eastern areas, with boundary just south of the CWA and less mixy
southeast flow across the area. As a result, will hold onto dew
points in the 60s throughout the day, with highs from lower 80s in
southwest Minnesota, to mid-upper 90s in south central South Dakota.

Boundary lifts northward Sunday night, followed by increasing south
to southwest winds, and expansion of 90 degree temperatures back
into eastern portions of the region. Some uncertainty developing in
pattern Sunday/Monday, with American models (GFS/NAM) indicating a
stronger wave developing across northeast Colorado on Sunday, then
slowly tracking northeast across Nebraska Sunday night and Monday.
This wave induces a pocket of convection over central to eastern
Nebraska, and into the Missouri River Valley, by late Monday, while
CMC/ECMWF keep that area dry with convective chances focused on the
frontal boundary in central-northeast South Dakota. Will carry a
small pop into the Missouri Valley Monday afternoon/evening to
account for these American solutions, but focus does remain near the
boundary as it slips into our far northern counties late Monday into
Monday night. As for temperatures, the convection in the GFS/NAM
results in a pocket of not-as-hot air in our far south/southwest,
while the CMC/ECMWF hang onto the warmer air with the more dominant
thermal ridge in the area. Given uncertainty in this period, did not
alter blended temperatures, but overall still leaning toward the
warmer solutions for highs on Monday.

Mid to late week period features a flatter upper flow across the
northern Plains, with a fair amount of model discrepancy regarding
the position of low level boundaries/upper level jet, along with
timing of various weak waves tracking through the region. This will
lead to periodic storm chances, with low confidence in timing and
location at this point. Confidence slightly higher that temperatures
will ease a bit from the weekend/early week heat, though highs in
the 80s to lower 90s still expected to be common through the period.
Humidity will also be a dominant feature through the mid-late week
period, which should hold overnight lows in the mid 60s-lower 70s,
but could also result in an extended period of afternoon heat index
values in the mid to maybe upper 90s. The latter will be dependent
on boundary position and convective timing, but areas south of I-90
currently look to be more prone to the higher heat indices than
areas farther north.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1020 PM CDT Fri Jul 14 2017

VFR conditions expected through the TAF period.




SHORT TERM...Heitkamp
AVIATION...JM is the U.S. government's official web portal to all federal, state and local government web resources and services.