797 
FXUS63 KUNR 272101
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
301 PM MDT Wed Jun 27 2018

.DISCUSSION...(This Evening Through Wednesday)
Issued at 300 PM MDT Wed Jun 27 2018

Current surface analysis shows cool front well south and east of 
the region with weak high pressure north of the area. Upper level 
analysis shows near zonal flow across the area at this time, with 
high pressure over the Four Corners region. Skies are sunny to 
partly cloudy across the area. Isolated thunderstorms have develop
over the northern Black Hills area this afternoon, but have had a
hard time sustaining themselves. Temps are in the mid 70s to mid 
80s across the area with light winds. 

A more unsettled pattern will return for the latter part of the week 
as a long wave trough along the west coast moves east across the 
Rockies and into the Plains later tomorrow through Saturday. A few 
showers and storms are possible later tonight into early Thursday 
across mainly northwest SD as a modest low level jet and theta-e 
advection develops over western SD. Weak ridging will build across 
the region later tonight into Thursday, with hot temperatures across 
the area Thursday afternoon, upper 80s and 90s. A cold front and low 
pressure system will move east across WY and MT in the afternoon, 
approaching our forecast area late in the day. Capping in place 
should hold fairly strong until late afternoon/early evening when 
the front arrives. Various models differ on exact location and 
timing of better thunderstorm chances late Thursday into Thursday 
night, but should primarily be focused across northwest SD into ND. 
Surface trough/dryline ahead of the front will move into the Black 
Hills area in the afternoon. The best instability and shear will be 
north and east of the Black Hills late in the day, with MLCAPE 
values of 2000 to 3000 j/kg. There is a slight risk to enhanced risk 
of severe storms north and northeast of the Black Hills, mainly for 
the evening hours, when the front passes through the area. 

Cooler and unsettled weather can be expected for Friday and Saturday 
as the trough moves across the Rockies and into the Plains. The best 
chances for showers and storms will be Friday afternoon through 
early Saturday evening. Chances for stronger storms and higher 
rainfall amounts will shift more toward areas south of interstate 
90. As the trough shifts east of the region later in the weekend, a 
drier and eventually warmer pattern should return for Sunday into 
the early part of next week. Some differences between the GFS and EC 
on overall pattern across the region toward the Independence Day 
holiday, but it generally looks at least seasonably warm with the 
potential for at least isolated storms Tuesday and Wednesday.  

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1131 AM MDT Wed Jun 27 2018

Other than some MVFR conditions in afternoon/evening 
showers/storms over the Black Hills area, VFR conditions are 
expected through Thursday morning. 

&&

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

$$

DISCUSSION...26
AVIATION...13