Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 282109
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
309 PM MDT Wed Jun 28 2017

.DISCUSSION...(This Evening Through Wednesday)
Issued at 309 PM MDT Wed Jun 28 2017

Current surface analysis shows low pressure over southeast WY,
with frontal boundary hanging across southern WY and into the
Central Plains. Upper level analysis shows near zonal flow across
the region, with upper low across central Canada. Shortwave trough
to the southwest of the low is digging southeast across the
Canadian Rockies and into the northern Rockies. Regional radars
show showers and thunderstorms have developed across the higher
terrain of southern MT and WY, now pushing onto the Plains. KUDX
radar shows some activity has now developed across northeast WY,
with an isolated strong storm south of Rapid City. Temps are in
the upper 70s and 80s with north to northwest winds in most
places.

Unsettled weather can be expected through at least early Friday as
shortwave slides slowly southeast into the region. For late this
afternoon into the evening, MLCAPE values will be most favorable for
stronger storms from far northeast WY through the Black Hills and
into parts of southwest SD, 500 to 1000 j/kg. Shear will be
sufficient for possible short-lived supercells. Marginal risk looks
appropriate for this afternoon/early evening with hail up to around
quarter size and gusty winds possible with the stronger storms.
Isolated to scattered showers and storms will linger overnight and
into Thursday morning across much of the area.

There should be a break in most areas during the late morning and
early afternoon Thursday before more activity develops later in the
afternoon and evening. The threat for stronger storms looks to
remain across mostly far southern SD and possibly into southern
parts of northeast WY where the better instability and shear will be
in place. Highs Thursday will be on the cooler side, mostly in the
70s, with some 60s over northeast WY and the Black Hills.

Any lingering activity should be limited to eastern portions of the
CWA on Friday as the main shortwave exits the region. Ridge will
build over the Rockies on Friday behind the exiting wave and then
slowly push east into the area over the weekend, with mainly dry and
warmer conditions expected. Ridge looks to break down late in the
weekend as shortwave energy crosses the region. Will keep chances
for storms later Sunday into Sunday night, especially for areas
south and east of the Black Hills. Isolated storms are possible
Monday as well. Building ridge may keep Independence Day dry and
warm.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1210 PM MDT Wed Jun 28 2017

VFR conditions will prevail outside of -TSRA through the period.
Partly cloudy skies this afternoon will be replaced by VFR BKN
CU/SC deck by late afternoon. Scattered -TSRA will develop over
northeast WY this afternoon and spread east through tonight with
local MVFR conditions. Very gusty 30-40kt winds can be expected
near storms.


&&

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

$$

DISCUSSION...26
AVIATION...15


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