Severe Thunderstorm Warning 55, NWS Rapid City, SD

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
245 PM MDT Tue Jun 27 2017

.DISCUSSION...(This Evening Through Tuesday)
Issued at 205 PM MDT Tue Jun 27 2017

Upper level analysis has a ridge over the northern Plains, with a
strong trof crossing the northern Rockies. Some high clouds are
streaming across the northern plains, with showers and storms
developing across central Wyoming. At the surface, cold front has
just moved through Rapid City, with very warm and dry air moving
in from the west. Strong southerly boundary layer flow across the
South Dakota plains has temps in the 80s to around 90 degrees at 2
PM, with dewpoints in the 50s.

Late this Afternoon/Tonight...Surface cold front will continue
east this afternoon, with the Cap eroding by late afternoon/early
evening. Models showing 2-3K J/kg CAPE across central SD as Cap
erodes. Thunderstorms are expected to develop well east of the
Black Hills, with some strong storms possible. CAMs are showing a
line of storms developing from Lemmon south to Philip and Martin
by 5-6PM, moving east into central SD early this evening. Main
threats will be large hail and damaging winds. Further west -
closer to the upper trof - ongoing showers and thunderstorms in
central WY will move into northeast WY and western SD this
afternoon and evening. These storms moving in behind the front in
the drier air will be high based, and likely producing more wind
than hail. On and off showers and storms will move through the
area overnight into early Wednesday morning.

Wednesday...Upper trof quickly shifts east with zonal flow taking
over through Wednesday night. Temps will be about 10 degrees
cooler on Wednesday behind the cold front. Another weak shortwave
associated with the upper trough will produce showers/storms
across northeastern WY and the Black Hills in the afternoon. With
ML CAPE of 600 to 1000 J/kg and 0-6 km shear of 40-50 kts, could
support and isolated strong to severe storm. Then chances for
showers/storms will expand across the CWA overnight.

Thursday and Beyond...Another lobe of the main upper trof will
swing through the northern Plains on Thursday, continuing chances
for showers and thunderstorm. Cool air will continue to wrap into
the region, with highs Thursday and Friday in the 70s. Mainly dry
weather is expected for Friday and Saturday, as an upper ridge
builds over the western CONUS, and a warming trend will begin.

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1106 AM MDT Tue Jun 27 2017

VFR conditions are expected through most of the afternoon. Sct
TSRA will develop along a cold front late this afternoon/evening
with local MVFR/IFR conditions along with the possibility of hail
and gusty winds. TSRA will move out of the region late this
evening.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

DISCUSSION...15
AVIATION...Johnson

Hazardous Weather Outlook
National Weather Service Rapid City SD
1126 AM MDT Tue Jun 27 2017

SDZ001-012-024-025-072-WYZ054>058-071-281300-
Harding-Butte-Northern Black Hills-Northern Foot Hills-
Sturgis/Piedmont Foot Hills-Northern Campbell-Southern Campbell-
Western Crook-Wyoming Black Hills-Weston-Northeastern Crook-
1126 AM MDT Tue Jun 27 2017

This Hazardous weather outlook is for portions of the Black Hills
of South Dakota...western South Dakota...northeast Wyoming...and
the Black Hills of Wyoming.

.DAY ONE...This Afternoon and Tonight

Scattered thunderstorms will develop late this afternoon and
persist into the evening hours. Isolated severe thunderstorms with
large hail and damaging winds are possible.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Isolated to scattered thunderstorms are possible Wednesday and
Thursday, but organized severe thunderstorms are not expected.

.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

SDZ002-013-014-026>032-041>044-046-047-049-073-074-281300-
Perkins-Northern Meade Co Plains-Ziebach-Rapid City-
Southern Foot Hills-Central Black Hills-Southern Black Hills-
Custer Co Plains-Pennington Co Plains-Haakon-Fall River-
Oglala Lakota-Jackson-Bennett-Mellette-Todd-Tripp-
Southern Meade Co Plains-Hermosa Foot Hills-
1126 AM MDT Tue Jun 27 2017 /1226 PM CDT Tue Jun 27 2017/

This Hazardous weather outlook is for portions of south central
South Dakota...the Black Hills of South Dakota...and western
South Dakota.

.DAY ONE...This Afternoon and Tonight

Scattered thunderstorms will develop late this afternoon and
persist into the evening hours. There is a slight risk of severe
thunderstorms with hail greater than 2 inches in diameter and wind
gusts from 60 to 70 MPH. An isolated tornado is possible, mainly
over south central South Dakota.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Isolated to scattered thunderstorms are possible Wednesday and
Thursday, but organized severe thunderstorms are not expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed late this afternoon and early
this evening, especially over south central South Dakota.

&&

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

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