Area Forecast Discussion
Issued by NWS Rapid City, SD

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373
FXUS63 KUNR 272352
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
552 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.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 531 PM MDT Tue Jun 27 2017

Sct TSRA will continue to move along a cold front this evening
across southern SD with local MVFR/IFR conditions along with hail
and 60-70kt winds. TSRA will move out of the region late this
evening. Additional thunderstorms are expected overnight into
early Wednesday morning with local IFR conditions.

&&

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

$$

DISCUSSION...15
AVIATION...15



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