Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 161708

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1108 AM MDT Mon Jul 16 2018

.DISCUSSION...(Today Through Sunday)
Issued at 321 AM MDT Mon Jul 16 2018

Northwesterly flow aloft exists today as the forecast area is
located between an upper ridge over the western CONUS and an upper
low/trough moving eastward across Manitoba/Ontario. At the
surface, weak high pressure is in place over much of the northern
plains with a weakly defined area of low pressure deepening over
the western third of the CONUS.

For today, weak capping will be overcome by diurnal heating and
large scale ascent associated with an approaching shortwave
trough. Steep mid-level lapse rates coupled with positive theta-e
advection, and moist southeasterly low level flow will lead to
thunderstorm development, first early this afternoon over the
Blkhls and then over northeastern Wyoming and possibly on the
plains of western SD later in the afternoon, continuing into this
evening. Supercells will be possible over the Black Hills given
SE upslope flow regime and increasing bulk shear. Convection will
shift SE tonight with perhaps some elevated thunderstorms late as
the main impulse advances east. Better coverage for storms is
expected on Tuesday as most of the remaining NW CONUS impulse
pushes east. Decent shear values with ample LL moisture will again
support a severe threat, esp from NE WY into scentral SD. Good
chances for precip expected Tue night into Wed for much of the FA
as the upper trough shifts east. Warmer/drier weather expected by
the end of the week as flow becomes less unsettled. Still expect
some ISOLD TS at times though, esp around the Black Hills. Temps
are expected to be seasonable, becoming warmer toward the


.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1108 AM MDT Mon Jul 16 2018

SCT TSRA will develop over northeastern WY and southwestern/south
central SD beginning mid-afternoon, with activity continuing into
the early overnight period. Localized MVFR/IFR conditions are
possible in these TSRA, along with the potential for hail and
gusty winds in the strongest storms. Latest guidance suggests TSRA
will remain south and east of KRAP, but will monitor trends for
potential addition of a TEMPO group for VCTS this afternoon or

Otherwise, VFR conditions are expected through the period.




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