Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 162341
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
641 PM CDT Sun Jul 16 2017

.SHORT TERM...(This evening through Monday)
Issued at 421 PM CDT Sun Jul 16 2017

Drier air has filtered into a majority of the CWA today thanks in
part to high pressure over the Great lakes. Areas along the Missouri
River however remain with dew points near 70 degrees as moisture has
pooled along and just behind a frontal boundary across Nebraska and
western Iowa.  Temperatures have again climbed near to above normal
in many areas, a sign of the recent warm and dry times.

Tonight: Winds will turn rather light this evening, before turning
to the south  and southwest by daybreak Monday as a frontal boundary
moves through. Persistent light warm advection aloft should keep our
lows tonight very balmy. It`s possible to have a few scattered mid-
level clouds drifting through, which could provide a bit of a "fly
in the ointment" for the Aurora lights viewing.

Monday: Very warm and humid day anticipated for the forecast area.
Temperatures should climb fairly quickly in the morning and dew
points again return towards the 70 degree mark.  Will need to watch
a compact shortwave currently in eastern Colorado as it moves across
Nebraska during the day. NAM is the most aggressive with this wave
pulling cloud cover and cooler temperatures into the MRV. This will
need to be monitored for it`s impact on temperatures.  If other
model solns verify, temperatures will again soar into the 90s, and
with increased dew points, heat index values jump to around the 100
degree mark.  Through collaboration, have decided to wait on any
heat advisory products.

.LONG TERM...(Monday night through Sunday)
Issued at 421 PM CDT Sun Jul 16 2017

Convection will continue to encroach on the western/northern CWA
heading through the evening hours with deeper dynamics/frontal
forcing from the northern stream, and within shearing upper wave
slipping across Nebraska. These features may be just far enough
apart to keep conditions quiet through at least early evening, but
prospect for convection should increase heading later into the night
both from progression from the northwest, and from expansion through
deformation between shearing upper low and the northern stream
dynamics. A few severe storms will be possible toward highway 14,
mainly late evening into the early overnight, on the edge of the
stronger deep layer shear and with plenty of potential elevated
instability.

Overall, the important message for the week in the forecast will be
the daily potential for thunderstorms, maximizing Tue./Wed. and
another increased threat late week.  This is largely driven by a
large scale pattern which will exhibit a flat ridge aloft, with
periodic waves strengthening the flow, and a low-level boundary
hanging at least in the neighborhood which will focus moisture and
at least the initial round or two of convection. With the core of
the upper ridge easing toward the southeast U.S. late week, flow
will become more favorable again for return flow again late in the
period.

The synoptic boundary on Tuesday is suggested to gradually
settle toward a Marshall to Sioux Falls to Pickstown line late day.
With wave passing by in the morning, and lingering veered low-level
jet and tail of wave could act to reinvigorate some convection
during the latter afternoon or early evening around southwest MN
where a few boundaries will fester through the day, with additional
development more spotty back along the frontal boundary. Again,
shear/instability parameters suggest at least a low-end severe
threat. Higher low-level moisture brings a quite humid day for most,
with some heat index values around 100 degrees through the Missouri
River corridor.

For the remainder of the week, the challenge will be timing of
waves, impact on boundary location, and the eventual favored
locations for convection. Models continue to fluctuate on timing of
waves, but in general have the weaker wave early Tuesday, a stronger
wave on Wednesday, and some semblance of a wave of monsoonal origin
around later Thursday night into Friday.  Proximity of the hot air,
high humidity, potential outflow reinforced boundary locations will
mean potential for some fairly significant gradients in temperature
and heat index as well.  Through Wednesday, would likely keep some
stifling heat index values in the neighborhood, especially the
Missouri River valley.  Not quite as extreme in the cards for the
worst of the heat at the end of the week, as brief greater influence
from slight west-northwest upper flow induces boundary southward.

Larger scale pattern is not unlike that favoring development of a
significant MCS on Wednesday into Wednesday night, perhaps even
toward that favoring a progressive derecho initiating around our
area during the afternoon/early evening. Much remains to be seen
where the component elements set up around earlier convection.
It is also important to note that while there will be an almost
daily chance for storms (tendency to be weighted more nocturnally-
early morning in this pattern), it is not a given that all will get
rainfall.  Some areas could receive quite a bit of rainfall this
week, while others do not share in the bounty. Details will
gradually iron out this week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 636 PM CDT Sun Jul 16 2017

VFR conditions are expected through the TAF period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Dux
LONG TERM...Chapman
AVIATION...



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