Hail and Damaging Winds in South Dakota, May 20, 2020

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
126 PM MDT Wed May 20 2020

.DISCUSSION...(This Evening Through Wednesday)
Issued at 126 PM MDT Wed May 20 2020

Deep western CONUS upper trough will slowly shift east and
support increasing chances for TS in the western third through
this evening. Main impulse and associated jet streak will push
into the area late this afternoon and evening, supporting a narrow
corridor of SHRA/TS, initiating off the Laramie Range. Copious
amounts of moisture are located over eastern NE WY and far western
SD with mean PW over an inch, well above climo norms. Still
expecting that a few storms will be capable of locally heavy rain.
The severe threat still looks valid, given Bulk layer (0-6km)
shear around 35-40 knots, with mean CAPE of 1.5-2 kJ/kg. However
the area and time window of these parameters overlapping will be
very narrow, mainly focused over Weston and Crook counties as the
dry line has already pushed east across much of Campbell county.
This should support a mixed hail and wind threat, transitioning to
more of a wind/hvy rain threat in the evening, with activity
being more isolated in nature later in the evening. Deep southerly
flow will tend to support fast storm motion to the NNE, with most
models struggling to carry the expected TS complex east much into
western SD. Hence, most of the rain may be limited to NE WY and
perhaps the western Black Hills in SD. If the TS complex does die
out over the Black Hills, strong downslope winds could develop
over the Northern Black Hills foothills this evening as the
outflow collapses. Precip will end west to east tonight with bulk
of precip shifting into far NW SD and waning. Elevated convection
will then be possible over south central SD overnight, per LLJ
forcing. Dry SW flow will spread across most of the FA by
Thursday, with perhaps a few lingering showers being possible
across far eastern portions of scentral SD where lingering
moisture and instability will reside. Virga may also develop
diurnally in the afternoon across the far west per steep ll lapse
rates.

Otherwise, mean upper trough will then stall in the NW CONUS and
support semi-unsettled conds into early next week with mainly
seasonal temps and a brief cool down Sunday. There is growing
support for cooler conds toward the end of next week as the upper
trough shifts east and supports a period of local NW flow.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1220 PM MDT Wed May 20 2020

TSRA will develop over nern WY/the Black Hills in the mid to late
afternoon, then spread E/NE through the evening. Some storms will
be capable of strong-severe winds and large hail. Storm activity
may linger overnight across west to central SD, but will not be as
strong.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 8 PM MDT this evening for SDZ001-002-012>014.

WY...None.
&&

DISCUSSION...JC
AVIATION...13

Hazardous Weather Outlook
National Weather Service Rapid City SD
534 AM MDT Wed May 20 2020

SDZ001-002-012-013-024>031-041-042-072>074-WYZ054>058-071-211300-
Harding-Perkins-Butte-Northern Meade Co Plains-
Northern Black Hills-Northern Foot Hills-Rapid City-
Southern Foot Hills-Central Black Hills-Southern Black Hills-
Custer Co Plains-Pennington Co Plains-Fall River-Oglala Lakota-
Sturgis/Piedmont Foot Hills-Southern Meade Co Plains-
Hermosa Foot Hills-Northern Campbell-Southern Campbell-
Western Crook-Wyoming Black Hills-Weston-Northeastern Crook-
534 AM MDT Wed May 20 2020

This Hazardous Weather Outlook is for portions of northwestern
South Dakota...southwestern South Dakota...the Black Hills of
South Dakota...northeast Wyoming...and the Black Hills of
Wyoming.

.DAY ONE...Today and Tonight

Strong to severe thunderstorms are expected this afternoon
through this evening. Primary hazards will be very large hail,
damaging winds, and heavy rainfall that could produce localized
flash flooding. While not the main concern, a tornado also cannot
be ruled out.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Additional rounds of thunderstorms are expected over the next
several days. A few strong to severe thunderstorms will be
possible Thursday and Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed today.

&&

Stay tuned to NOAA weather radio for further updates...or check
our web site at weather.gov/rapidcity

SDZ014-032-043-044-046-047-049-211300-
Ziebach-Haakon-Jackson-Bennett-Mellette-Todd-Tripp-
534 AM MDT Wed May 20 2020 /634 AM CDT Wed May 20 2020/

This Hazardous Weather Outlook is for portions of western South
Dakota.

.DAY ONE...Today and Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Strong to severe thunderstorms are possible Thursday. The primary
concerns will be hail and strong winds.

Additional rounds of thunderstorms are expected over the next
several days. A few strong to severe thunderstorms will be
possible again on Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today.

&&

Stay tuned to NOAA weather radio for further updates...or check
our web site at weather.gov/rapidcity

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RAPID CITY SD
441 PM MDT WED MAY 20 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0432 PM     TSTM WND GST     ROZET                   44.28N 105.20W
05/20/2020  E50 MPH          CAMPBELL           WY   NWS EMPLOYEE

            OUTFLOW STARTING TO GET AHEAD OF STORM

&&

EVENT NUMBER UNR2001591

WFO UNR

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