915 
FXUS63 KUNR 151138
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
538 AM MDT Wed May 15 2019

.DISCUSSION...(Today Through Tuesday)
Issued at 315 AM MDT Wed May 15 2019

Current surface analysis shows nearly stationary warm front over 
the area, with clear to partly cloudy conditions and light winds 
in most areas. Upper level analysis shows ridge slowly shifting 
east over the high plains, with weak shortwave that brought some 
showers and storms late yesterday into the overnight now to the 
southeast of the forecast area. Temps are mostly in the 50s right 
now, with some 40s over the Black Hills. 

Ridge over the area will help to bring mostly quiet wx for today. It 
will be a warm day, with highs in the 80s across the plains, 70s 
over the Black Hills. Main shortwave passing through the ridge later 
today will track across ND into north central and northeast SD. A 
few showers/storms could clip far northeastern portions of the 
forecast area late today into the evening, with gusty winds and hail 
a possibility with any stronger storms. Upper level support for 
storm development will be minimal elsewhere. However, some embedded 
energy within the ridge may be just enough to get isolated storms to 
develop from parts of northeast WY into southwest SD this afternoon 
and evening, especially the higher terrain of the Black Hills. The 
main threat from a stronger storm in these areas would be brief 
gusty winds, with forecast MUCAPE values generally around 500 j/kg 
and relatively weak shear.  

Ridge will shift east of the area by early Thursday, allowing a cold 
front to slowly sag south across the area on Thursday. Highs will 
range from the lower 70s across northwest SD to the low to mid 80s 
across far southern SD. Energy within southwest flow aloft on the 
back side of the ridge will interact with the front to bring a good 
chance of showers and thunderstorms Thursday afternoon and night. 
The best threat for storms, along with possibly a few strong to 
severe ones, will be in closer vicinity to the cold front from 
northeast WY to the Black Hills and far southern SD later in the 
day. Cape values of 1000 to 1500 j/kg and moderate shear could 
produce storms with at least marginally severe hail and strong wind 
gusts. Some heavy rainfall is likely with the stronger storms as 
well. 

Large upper trough will move across the western US Friday and into 
the Plains over the weekend, with a cooling trend and very unsettled 
weather expected. Surface low pressure will develop over the central 
high plains on Friday, with front likely staying south of the area. 
There will likely be an outbreak of severe weather across much of 
the central plains and southern high plains Friday. There is 
potential for strong to severe storms to clip at least areas south 
and east of the Black Hills, but this will ultimately depend on the 
position of the surface low and how much instability can make it 
into the area by late in the day. The latest NAM solution is the 
most favorable for the possibility of severe storms compared to the 
EC and especially the GFS. The weekend looks to be quite cool and at 
least occasionally wet as the trough moves into the plains, with a 
pair of upper lows likely within the trough. The exact track of the 
lows will determine how much pcpn the area will receive, but the 
heaviest of pcpn should generally be late Friday into Saturday. EC 
is especially cold, with the potential for some snowfall across at 
least the Black Hills and possibly onto the plains of northeast WY 
and far western SD later Saturday night into Sunday. 

There will likely be a break in pcpn chances late this weekend into 
Monday, but yet another large storm system is expected to move 
across the west and into the plains Tuesday and Wednesday. Showers 
and cool weather will persist through the middle of next week. 

&&

.AVIATION...(For the 12Z TAFS Through 12Z Thursday Morning)
Issued At 535 AM MDT Wed May 15 2019

VFR conditions are forecast for the KRAP and KGCC aerodromes
through the valid period. Isolated showers and thunderstorms may
develop over the Black Hills aft 18z. Little if any impact to
terminal locations is expected. 

&&

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

$$

DISCUSSION...26
AVIATION...Hintz