873 
FXUS63 KUNR 300440
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1040 PM MDT Thu Jun 29 2023

.DISCUSSION...(This Evening Through Thursday)
Issued at 116 PM MDT Thu Jun 29 2023

Upper-level analysis shows split flow over the western 
CONUS: a trough across much of the western US and ridging over the 
far NW. Water vapor imagery indicates a couple shortwaves over the 
Rockies. A couple of thunderstorms have developed over the central 
BH early this afternoon. At the surface, high pressure rests over 
WY, creating light NW winds across our CWA. Temperatures are rising 
into the 70s and 80s.

Trough and embedded shortwaves will slowly push into the northern 
plains today and Friday, sparking some thunderstorms across our 
area.  The likeliest place for severe storms will be across our SW 
CWA, where around 1500 J/kg MLCAPE will be collocated with 30-40 kts 
of 0-6 km shear. Elsewhere, either shear or buoyancy will be weaker. 
Heavy rain will be possible beneath any storm, but again the 
greatest potential will be our SW CWA, where precipitable waters 
will be around 150% of normal. CAMs depict storms initiating off the 
Black Hills and northeastern WY this afternoon, and potentially 
stronger storms across WY skirting our SW CWA this evening. 

Thunderstorms will diminish in severity tonight, but showers and 
weak storms, along with somewhat low clouds are expected to linger 
across the southern CWA through much of Friday. As a result, lowered 
highs for that area especially. More showers/storms are expected 
Friday afternoon/evening as the main trough crosses our area. Weaker 
shear/CAPE will decrease the threat for severe storms; however, an 
expanded area of ~150% PW and weaker mean flow increases the risk 
for heavy rain and potential flooding. 

Upper ridging over the western CONUS will result in a warmer and 
drier weekend, although a stray shower/storm cannot be ruled out. 
Highs will be in the 80s on the plains, 70s in the Hills. 

Early next week, a Canadian low pressure system will flatten the 
ridge, its embedded shortwaves will bring returning active weather, 
and a cold front will cool temperatures noticeably. The outlook for 
July 4th includes chances for thunderstorms, highs in the upper 60s 
to mid 80s, and breezy northwest winds.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1037 PM MDT Thu Jun 29 2023

Scattered TSRA will exit scentral SD this evening. Local IFR 
conditions expected with the storms, but otherwise, VFR conditions
expected through 09Z Friday. After 09Z, MVFR CIGS may develop 
over south central SD and persist through late Friday morning. 
More showers and storms are expected Friday, esp in the afternoon.

&&

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

$$

DISCUSSION...Pojorlie
AVIATION...JC