Area Forecast Discussion
Issued by NWS Rapid City, SD

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841
FXUS63 KUNR 210501
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1101 PM MDT Tue Jun 20 2017

.DISCUSSION...(This Evening Through Tuesday)
Issued at 256 PM MDT Tue Jun 20 2017

Current surface analysis shows stationary front near the Black
Hills, with high pressure centered over northeast ND. Upper level
analysis continues to show high pressure centered over eastern AZ,
with ridging to the north across the intermountain west.
Northwest flow aloft is in place across the Northern Plains. Skies
are mostly sunny across much of the area. Temps range from the
upper 70s across far northwest SD to around 90 over portions of
northeast WY and far southern SD. Winds are variable and mostly on
the lighter side across the area.

There still could be a shower or thunderstorm developing across
parts of far northeast WY and the northern Black Hills area late
this afternoon near the boundary. Otherwise, the main chances for
showers and storms should hold off until this evening when main
shortwave energy and cold front approach the area. Precipitation
chances will increase across northeast WY this evening and then
spread east across much of the area overnight. Southerly low level
jet will strengthen overnight east of the Black Hills, with modest
theta-e advection over central SD. Could see a stronger storm or two
over western areas in the evening, then possibly a strong to severe
storm later tonight to the east of the Black Hills, near the nose of
the low level jet. Gusty winds and hail will be the main threats
from any stronger storms. Activity will exit eastern portions of the
CWA late tonight/early Wednesday.

Cold front over the Pacific NW will move quickly across the Rockies
tonight and into western portions of the area Wednesday morning
before stalling out over western SD during the day. Highs on
Wednesday will range from the lower 80s over the Black Hills to near
95 over south central SD. A thunderstorm is possible over the Black
Hills in the afternoon. Another round of nocturnal convection is
possible Wednesday night as a weak disturbance aloft passes across
and eventually pushes the front east of the forecast area by
Thursday morning. Isolated strong to severe storms are possible near
and east of the front from southwest to central SD.

We will see a cooling trend for the rest of the week and into the
weekend, with Friday and Saturday being the coolest days. A
shortwave and Canadian cold front will slide southeast through the
area late Friday into Saturday, bringing a chance of showers and a
few storms. Mainly dry weather and warmer air will return late in
the weekend and early next week.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1058 PM MDT Tue Jun 20 2017

VFR conditions will prevail outside of TSRA through Wednesday.
Isolated to scattered TSRA will occur overnight, mainly east and
north of the Black Hills. Local MVFR conditions possible in/near
any storms. A period of gusty northwest winds are expected late
tonight through midday Wednesday behind a cold front. Additional
storms may develop as another disturbance moves through Wednesday
night.

&&

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

$$

DISCUSSION...26
AVIATION...Helgeson



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