257 
FXUS63 KUNR 142325
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
525 PM MDT Tue Aug 14 2018

.DISCUSSION...(This Evening Through Tuesday)
Issued at 322 PM MDT Tue Aug 14 2018

Current surface analysis shows cold front south and east of the 
forecast area. Upper level analysis shows an area of low pressure 
over eastern portions of the Central Plains, with a shortwave 
trough over the eastern half of MT. High pressure remains across 
the Four Corners region. Skies are variably cloudy with an area of
showers and thunderstorms over parts of southwest into south 
central SD, gradually dissipating. Regional radars show storms 
developing west of the forecast area, especially over the higher 
terrain. Temps are in the mid 60s to upper 70s, with winds 
southeasterly or becoming southeasterly across much of the area. 

Unsettled weather will continue over the next couple of days as the 
upper level system slowly moves across the Northern Plains. Storms 
to the west will move into northeast WY late this afternoon/early 
evening and into western SD this evening/overnight. The best 
instability late this afternoon and evening will be across eastern 
WY to far southwest SD, 1000 to 1500 j/kg MUCAPE. Shear will be 
quite favorable for stronger storms/supercells across northeast WY. 
There is a slight risk for severe storms across northeast WY with 
large hail and strong wind gusts the main threats. Shear profile in 
the lower levels would suggest that a tornadic storm cannot be ruled 
out over northeast WY as well late today. With precipitable water 
values 125 to 150 percent of average, there will be locally heavy 
rainfall with stronger storms today and tonight. 

The trough will close off over the Northern Plains Wednesday and 
Wednesday night, with scattered to numerous showers and 
thunderstorms expected in many areas. The exceptions will likely be 
across western parts of northeast WY and far northwest SD. Forecast 
instability will be sufficient for stronger storms from the Black 
Hills eastward in the afternoon/early evening. Highs will
generally be in the 70s to around 80. Activity will slowly end 
from west to east late Wednesday and Wednesday night. Will keep 
some low chances across south central SD into Thursday. Otherwise,
warmer and mainly dry weather is expected Thursday into Friday as
a shortwave ridge moves across the region. 

Another fairly strong upper level system for this time of year will 
move across the area over the weekend, bringing good chances for 
showers and storms Saturday and Sunday. There is potential for some 
severe storms and heavier rainfall across at least portions of the 
area. That system will exit early in the week, with some drier 
weather returning for the first half of the week.  

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 523 PM MDT Tue Aug 14 2018

Strong thunderstorms over northeastern Wyoming will continue
eastward into western South Dakota this evening and overnight 
with local IFR conditions. Outside of any storms, VFR conditions 
are expected through the period.

&&

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

$$

DISCUSSION...26
AVIATION...10