Tornadoes and Damaging Winds in South Dakota, August 27 to 28, 2020

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
850 PM CDT Thu Aug 27 2020

.UPDATE...
Issued at 847 PM CDT Thu Aug 27 2020

Storms are forming over the High Plains now, and with good shear
and instability over the region, expect that activity to congeal
into a forward propagating MCS later tonight, with strong winds
being the main threat the later we go into the evening. Storms
will likely ride along and north of the edge of the EML over
southern South Dakota. Temperatures look fine for the overnight
low.

&&

.SHORT TERM...(This Evening through Friday Night)
Issued at 432 PM CDT Thu Aug 27 2020

The main challenge in this forecast period surround tonight's
chances for severe thunderstorms. So far through today's daytime
period, portions of the area have remained partly to mostly cloudy
with scattered showers and thunderstorms affecting some spots. Most,
if not all of this activity has been fairly benign. Anticipate this
precip currently out there at mid afternoon will remain sub severe
as it progresses eastward across the northern CWA zones and far
southern zones.

Lee of Black Hills low pressure at the sfc will continue to organize
the remainder of the afternoon with an inverted trough extending
northward across the western Dakotas toward another low pressure
center across northeast MT/northwest ND. Aloft, we have a favorable
setup with an upper trough across the western CONUS with embedded
s/w energy rotating through the flow across the northern High
Plains. All of these features will progress eastward this evening
into the overnight hours. Instability and shear are progged to
remain favorable through this time across most of the CWA and parts
of the region. So, the setup is good for a round of severe
thunderstorms to break out later this evening west of our FA and
trek eastward into our CWA late tonight through early Friday
morning. Initial threats from any activity will be large to very
large hail and damaging winds. As clusters of storm congeal later
and move east, damaging to destructive wind gusts will become more
of the primary threat along with an isolated tornado or two. CAM
solutions show the first cluster of storms to perhaps develop around
the Black Hills region this evening and slide eastward and
potentially threaten our southern/southwestern zones during the
early to mid evening hours. CAMs also depict another round, perhaps
more potent area of storms developing farther to the north and west
of the Black Hills and rolling east with time that could affect more
of our northern, central and northeastern zones late tonight into
early Friday morning. This cluster of storms potentially could be
more of the stronger wind producers as they congeal and form bowing
segments late tonight. Damaging winds up to and in excess of 70-80
mph could be a possibility with these stronger storms.

Any storms that linger into the morning hours should exit to our
east into MN and out of the CWA toward sunrise or by mid morning.
High pressure will slowly build in through the day Friday delivering
drier, more comfortable and stable air on northwesterly winds. After
going through the overnight hours with temperature readings in the
60s, daytime highs on Friday will remain on the cooler side of
average in the mid to upper 70s.

.LONG TERM...(Saturday through Thursday)
Issued at 432 PM CDT Thu Aug 27 2020

The long term is still on track for a big cool down for next week.
Until then, a upper ridge axis will move over the region Saturday
and Saturday night while an upper level trough over the Pacific
Northwest begins to move towards our region.  At the surface,
Saturday will be a cooler than normal and dry day as a surface high
pressure area builds east and winds turn south. There will be an
initial short wave trough in the westerly flow along with waa
bringing chances of showers and storms Saturday night into Sunday
morning. Then the pressure falls and a tightening surface pressure
gradient on Sunday will bring increasing south winds, warmer
temperatures, along with increasing moisture and instability. With
the upper level lift and cooling from the upper low pressure trough
coming in from the northwest along with strong surface forcing from
the cold front, storms are expected to develop and move quickly
across the region Sunday night into Monday morning. The big cool
down will be on Monday as Canadian air moves in. Another short wave
will bring a chance of showers/storms Monday night into Tuesday with
dry weather for Wednesday and Thursday. A large upper low pressure
area developing in eastern Canada with upper ridging along the west
coast will keep our region in cooler northwest flow through the end
of the week. Sunday will be the warmest day with mainly 80s and
lower 90s. Monday through Thursday will be mostly in the 70s to the
lower 80s with some locations only reaching the upper 60s on
Monday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 624 PM CDT Thu Aug 27 2020

Terminals KABR,KATY,KPIR,KMBG

Mainly VFR conditions are expected overnight. However, brief
periods of IFR conditions, and strong winds are possible with
thunderstorms later tonight.

***Construction to improve taxiways at both KABR/KPIR terminals
may cause an occasional temporary visibility reduction due
to blowing dust (bldu), mainly during daytime hours UFN.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

UPDATE...TDK
SHORT TERM...Vipond
LONG TERM...Mohr
AVIATION...TDK

Hazardous Weather Outlook...UPDATED
National Weather Service Aberdeen SD
427 PM CDT Thu Aug 27 2020

MNZ039-046-SDZ003>011-015>023-033>037-045-048-051-282130-
Traverse-Big Stone-Corson-Campbell-McPherson-Brown-Marshall-Roberts-
Walworth-Edmunds-Day-Dewey-Potter-Faulk-Spink-Clark-Codington-Grant-
Hamlin-Deuel-Stanley-Sully-Hughes-Hyde-Hand-Jones-Lyman-Buffalo-
427 PM CDT Thu Aug 27 2020 /327 PM MDT Thu Aug 27 2020/

This Hazardous Weather Outlook is for west central Minnesota,
central South Dakota, north central South Dakota and northeast
South Dakota.

.DAY ONE...Tonight.

Thunderstorms are expected to move quickly across the region this
evening into the early Friday morning. Some severe storms are
expected with damaging winds and large hail. Wind gusts of 70 to 80
mph or higher are possible along with a possible tornado.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Thunderstorms are expected again Saturday night, Sunday, Sunday
night into Monday morning.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed. Weather spotters are
encouraged to submit reports to the National Weather Service in
Aberdeen. The public can submit reports on our web page, Facebook
page, or our Twitter feed.

Mohr