Hail and Damaging Wind in South Dakota, July 5, 2016

Area Forecast Discussion
National Weather Service Sioux Falls SD
340 PM CDT TUE JUL 5 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 340 PM CDT Tue Jul 5 2016

Surge of lower to mid 70s dewpoints has pushed into the eastern two-
thirds of the FSD CWA by early afternoon. This generally a result of
strong cap in place across the area, a very unstable mid-level layer
which has kept spotty ACCAS showers and storms across the southern
portions of the CWA through the day.  Clouds have somewhat limited
the warming potential as well, enhancing the strength of the surface-
based cap, but perhaps helping to partially erode some of the warm
layer aloft with evaporative cooling for some locations.

Focus for tonight is on the severe weather threat. Convection has
initiated in the last hour just to the east of KPIR, in area of lift
noted pushing out across western South Dakota along disturbance on
tail of wave moving along the International Border.  Temps a touch
cooler in mid-levels as well toward northwestern CWA, but from near-
surface conditions, the storm remains somewhat elevated in trailing
the triple point near surface wave northeast of KHON. Lift with this
wave likely to favor more northern portions of the frontal and post-
frontal convergence axes, but eventually shear in the 0-3km layer
suggests enough organization that should be able to overcome the cap
and progress east/southeast into a very potentially unstable air
mass.

Threats would start primarily as hail and wind, perhaps an isolated
tornado closer to Highway 14, but organization into more linear
structures suggesting a shift toward a higher wind threat with
smaller hail sizes. Winds perhaps as high as 80 to 90 mph north of
Interstate 90. DCAPE with the steep off-surface lapse rates very
high. Given large potential CAPE, hail up to 2 inches in diameter
likely in initial supercell storms toward the northern CWA.

By 03-04z, likely that outflow reinforced frontal boundary likely to
push into the far southern CWA. As secondary energy slides across
Nebraska, will likely see resurgence of some convection moving east
northeast toward the lower Missouri valley and northwest Iowa a
couple hours after initial frontal convection. These storms would
have a lesser threat, but still could produce some isolated severe
hail or wind through 06-07z.

For Wednesday, moist and unstable air with strong east/west banding
spreads back northwest and north into and across the Missouri River
area, but it appears that despite MLCAPE headed back up to 2000-4000
J/kg, decent CIN of 100-200 J/kg will hold off storms for most of
the day. The boundary at the surface will be diffuse, but enough
cooling tonight is expected to hold high temperatures Wednesday to
the 85 to 90 range, and that will help prevent much if any
initiation of storms during the day. However, there will be some
chance west of the James River by the end of the day, in line with
development of severe storms west of our forecast area as projected
by SPC.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 340 PM CDT Tue Jul 5 2016

Scattered to numerous storms should spread over the area from the
west Wednesday night, with existing storms, possibly in the form of
an MCS, taking advantage of the continuing strong CAPE with some
becoming severe. Storms will be affecting the area most of the
night, with repeat/training storms and some westward propagation of
any MCS possible in the very favorable westerly upper flow over the
lower level thermal and moisture banding. A decent mid level short
wave, which has been shown by models the past couple of days, will
be moving over the area during the night and will aid continued
development. Locally heavy rain and possibly even flash flooding
still appears to be a threat along with severe weather, but the
likely complicated convective pattern seems to prohibit defining a
greatest threat for now, and that threat could even be north of the
greatest severe threat. No flash flood watch for now, especially
given the recent fairly dry weather, but we will see if the threat
will become better defined in the next 12 to 24 hours.

Low temperatures Wednesday night will vary from the mid 60s north to
around 70 along the Missouri River.

Thursday will bring the arrival of a trough and cold front on the
heels of Wednesday night activity, and MLCAPE again up to 4000 J/kg
over the southeast part of the area. A risk of severe as depicted by
SPC seems right, especially given the decent dynamics provided by
the upper trough. High temperatures should be in the 80s area wide.

The EC has come around some to the cooler weather for friday,
followed by slow but steady warming from the west over the weekend
into early next week, as an upper ridge builds over the plains ahead
of an unusually strong July Pacific coast trough. Decent drying
should survive a couple of days of warm advection, with the chance
of storms reappearing very slowly late in the weekend into early
next week, as the moisture only slowly returns.

With the upper ridge developing between upper troughs, instead of
building strongly north from the southwest and southern plains, the
warming should be modest, with a return to 90s hard to come by.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 115 PM CDT Tue Jul 5 2016

Main aviation concern is potential convection and associated
hazards for later this afternoon and evening. At this time,
appears as if KHON should be spared development with surface wave
and associated low level convergence poised to pass the area by
mid afternoon. KFSD will have some challenge getting development
to extend deeper into the capping inversion, but would be most
likely by very late afternoon and very early evening. Slowing
boundary and deeper moisture could bring a little better chance
for a storm by early to mid evening around KSUX. Threat for hail
and strong winds with any storms, but very conditional on
development. Otherwise, potential if front/outflow manages to
stall near the southern edge of the CWA that KSUX could manage to
sneak in a little mvfr ceiling or visibility after 08z through
early to mid morning, but too low probability to mention at this
time.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

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

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