742
FXUS63 KUNR 040946
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
346 AM MDT Fri Jul 4 2025

.KEY MESSAGES...

- Scattered thunderstorms likely today. Severe weather isn`t
  expected, though stronger storms could produce heavy rainfall
  and small hail.

- Thunderstorms will affect the region again on Saturday afternoon
  and evening with scattered severe storms possible.

- Average to above average temperatures and chances for storms
  will continue through the next week.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 345 AM MDT Fri Jul 4 2025

Main concern in the forecast period will be daily chances for
thunderstorms through this weekend. Isolated severe storms are
possible across southwestern into south central SD this afternoon.
There is the potential for isolated to scattered severe storms
across much of the CWA Saturday evening. Currently, shower/storm
activity has calmed down across northeastern WY into northwestern
SD with only light returns showing up on radar. A SW-NE oriented
outflow boundary from this evening`s storms is currently draped
across Oglala Lakota and Jackson Counties. A solitary shower has
popped up along this boundary in the past few radar scans, fueled
by 1000 J/kg MUCAPE. Bulk shear is weak, generally less than 20
kts, so not expecting severe weather to develop out of this cell.
More isolated showers/storms may develop across south central SD
as the outflow boundary continues to move to the southeast.

More robust shortwave moves through the region today, bringing
increasing chances for showers and storms this afternoon and
evening, especially across southwestern into south central SD.
Marginal deep layer shear of 20-30kt could support a stronger
updraft or two with gusty winds being the primary concerns, though
overall severe threat will remain low. PWAT values of 150-175% of
normal will also support heavy rainfall in these storms.

Mostly zonal flow will develop over the northern tier of the US
for Saturday. Mid-level impulse will eject over the northern
plains with sfc low developing over WY. Ahead of the low,
southeasterly flow will advect warm, moist air into the region
with sfc DPs climbing into the upper 50s to low 60s across much
of western SD into northeastern WY. This should support the
development of a corridor of modest instability Saturday afternoon
with some areas seeing SBCAPE of 2000+ J/kg. Bulk shear values of
30-40kt will support organized updrafts with low level curvature
in the hodographs and steep low to mid level lapse rates of 7-8+
C/km indicating a large hail and damaging wind gust threat. Recent
4km NAM and HRRR runs have been fairly consistent in showing an
MCS over southeastern MT entering northwestern SD by late Saturday
evening.

Zonal flow will continue over the forecast area through the
beginning of next week with periodic disturbances along the flow
bringing occasional chances for thunderstorms to the region. Some
severe weather is possible, though confidence in timing, location,
and intensity drops off after Saturday.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1013 PM MDT Thu Jul 3 2025

VFR conditions expected to prevail through most of the period for
most areas. Isolated thunderstorms will be possible
overnight. Winds will shift to the northwest tonight as a cool
front moves through the area. Scattered showers and thunderstorms
can be expected once again Friday.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...JC