562
FXUS63 KUNR 252033
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
233 PM MDT Tue Jun 25 2024

.KEY MESSAGES...

- Above average temperatures through midweek with isolated to
  scattered showers and thunderstorms through Wednesday, mostly
  during the afternoon into nighttime hours, a few storms likely
  strong to severe each day.

- Better potential for severe storms later on Thursday as a cold
  front approaches the area.

- Becoming cooler and drier for Friday into the weekend.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 233 PM MDT Tue Jun 25 2024

Current surface analysis shows cool front across the central
plains into the Rockies, with low pressure along it across central
WY. A surface trough extends east-northeast from the low into
western SD. Upper level analysis shows near zonal flow across the
Rockies and Plains, with developing high pressure over NM and west
TX. Skies are clear to partly cloudy with temps mostly in the 80s
and light northeast to east winds. Isolated to scattered showers
and thunderstorms have developed early this afternoon along the
surface boundary over northwest into north central SD. This
activity is moving to the east-southeast toward the northern Black
Hills and west central SD.

Warm air will remain in place across the region, with above average
temperatures expected to continue through the midweek period. Highs
will reach the upper 70s to around 90 in most areas through
Thursday. Many of the CAMS continue to show isolated to scattered
storms moving/developing from mostly west central to south central
SD for the rest of the afternoon into the evening hours. Steep low
to mid level lapse rates are in place across these areas, helping to
produce MLCAPE values of 500 to over 1500 j/kg. Shear is sufficient
for isolated supercell development, especially east of the Black
Hills to south central SD. Large hail would likely be the primary
threat from any supercell storms, with stronger wind gusts more
likely accompanying linear convection. A tornado cannot totally be
ruled out either with any supercells toward south central SD later
today. Activity should taper off and exit southeastern portions
of the area by late evening. Frontal boundary remains southwest of
the area on Wednesday, with winds turning to the southeast during
the day. Increasing low level moisture will pool to the northeast
of the frontal boundary across much of eastern WY into southwest
SD and western NE. Upper high will strengthen over the Four
Corners area, with ridge building north across the Rockies. Enough
embedded energy within the trough will bring chances for showers
and thunderstorms later Wed afternoon and evening from at least
southern parts of northeast WY through southwest and south central
SD. Threat for stronger storms looks to stay mostly south of the
forecast area, but MUCAPE values up to 750 j/kg across far
southern SD could lead to a few stronger storms late in the day,
especially across far southwest SD. Strengthening low level jet
over eastern portions of the CWA into central SD/NE Wed night will
likely keep showers and storms going across areas northeast and
east of the Black Hills into early Thursday, with some beneficial
rains a good possibility.

Upper ridge moves over and east of the area on Thursday as an upper
trough moves from the Pacific NW into the northern Rockies. Low
pressure will move across MT, with frontal boundary lifting
northeast across the forecast area as a warm front. Chances for
storms will increase mid to late afternoon as upper energy moves
into the area ahead of the trough and MLCAPE values increase to 1000
to 2000 j/kg across much of the forecast area near and east of the
warm front. Further west, a surface trough/dryline looks like it
will move across northeast WY during the afternoon and into western
SD by the evening, helping to aid in storm development as well. The
better chances for severe storm development right now, a slight risk
at near or above 15 percent, looks to be from far northeast WY to
northwest SD, where better forcing aloft is expected. Chances drop
off some to the south and southeast of these areas, but there is
still some potential with uncertainty still existing on the track
and timing of upper level and surface features.

Trailing cold front should push through the area Thursday night
and early Friday, with much cooler conditions and brisk winds for
Friday. Highs look to mostly be in the upper 60s and 70s on Friday
and Saturday. Upper low will pass north of the area on Friday,
with some lingering chances for showers and isolated thunderstorms.
Drier air in place should keep most or all of the area dry on
Saturday. Passing shortwave ridge on Sunday will bring very warm
conditions back for Sunday and early next week. Another upper
trough likely passing north of the area Monday into Tuesday would
bring chances for storms during that time, especially across
northern portions of the forecast area.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1028 AM MDT Tue Jun 25 2024

Isolated thunderstorms are expected to develop this afternoon,
mainly over western SD. Severe storms are possible. Besides any
brief MVFR conditions near storms, VFR conditions will continue
through the TAF period.

&&

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

$$

DISCUSSION/KEY MESSAGES...26
AVIATION...Pojorlie