539
FXUS63 KUNR 182055
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
255 PM MDT Tue Jun 18 2024

.KEY MESSAGES...

- Mostly dry and cool weather through Wednesday, with patchy frost
  late tonight over northeast WY, the Black Hills, and northwest SD.

- Unsettled conditions return for Thursday and the late week period,
  with potential for some stronger storms on Friday.

- Becoming hot and mainly dry Sunday into early next week.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 255 PM MDT Tue Jun 18 2024

Current surface analysis shows cold front is well east of the
forecast area, with high pressure moving southeast across MT.
Upper level analysis shows larger scale trough across much of the
western into central US, with embedded shortwave moving northeast
across western ND into south central Canada. Skies are partly to
mostly sunny, with the most clouds across generally from far
northeast WY to northwest SD. Breezy conditions linger across much
of the area this afternoon with temps mostly in the upper 50s to
around 70 degrees.

Shortwave trough to the north will lift northeast out of the region
late today and this evening, with any showers clipping far northwest
SD tapering off. Skies will be clear to partly cloudy with winds
decreasing overnight. High pressure will pass over the area tonight
into early Wednesday. Cool and drier air in place tonight will allow
temps to drop into the mid/upper 30s and 40s by daybreak, with 30s
over the Black Hills. Patchy frost could develop late tonight in
some areas from northeast WY to northwest SD, with some freezing
temps across the higher Black Hills. Highs on Wednesday will reach
the upper 60s and lower 70s across much of the plains, 60s over the
Black Hills. There is potential for isolated showers over mainly far
northeast WY, the Black Hills, and northwest SD later in the
afternoon, but most areas should stay dry.

As high pressure moves east of the region Wednesday afternoon and
night, southeasterly winds develop across the area and help to bring
gradually warmer and moister air into the northern Plains. Temps
will be back closer to average levels late week into Saturday.
Southwesterly flow aloft becomes more pronounced late week as trough
along the west coast redevelops. Chances for showers and
thunderstorms will increase later Wednesday night and especially on
Thursday as low level moisture and mid level theta-e advection
increase, along with embedded energy aloft moving through the
Rockies and into the central/northern Plains. Would not rule out a
few stronger storms later on Thursday, especially across far
southwest into south central SD, where MUCAPE values are progged to
reach near 1000 j/kg. However, the better chances for strong to
severe storms look to be on Friday as stronger shortwave energy
moves across the northern/central high Plains. Where the better rain
chances/severe storm potential will be across our area would depend
on the track of the shortwave, with the GFS favoring a more
southerly track across the region compared to the EC. Shortwave will
likely exit the region Saturday, with improving conditions expected
from southwest to northeast.

Upper ridge moves across the western US early in the weekend and
into the Plains region for Sunday and early next week. Much warmer
air will build into the area, with highs expected to reach the 90s
across much of the Plains by Monday. Ridge is expected to weaken
toward the end of the forecast period as another system moves across
the Pacific NW into south central Canada and eventually drags a cold
front across the northern Plains.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1107 AM MDT Tue Jun 18 2024

AREAS MVFR/LCL IFR CIGS, along with some -SHRA, are possible over
northwestern South Dakota until around 03Z this evening. MVFR
CIGS over south central South Dakota will gradually improve to VFR
early this afternoon. Otherwise, VFR conditions will prevail
through the forecast period. Gusty northwest winds will continue
through this afternoon with winds diminishing this evening.

&&

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

$$

DISCUSSION/KEY MESSAGES...26
AVIATION...10