871
FXUS63 KUNR 030800
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
200 AM MDT Wed Jul 3 2024

.KEY MESSAGES...

- Organized severe thunderstorms possible this afternoon/evening
- Coolish 4th of July
- Warmer and progressively drier pattern starts Friday
- Hot/dry weather develops next week

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 156 AM MDT Wed Jul 3 2024

07z surface analysis had lee trough from central MT into
northeast CO. Weak shortwave ridge passing through CWA with quiet
weather in place. Upstream wave of interest over southern BC/AB,
the main weather maker for the short term.

Today/tonight, BC/AB shortwave drops southeast into the northern
plains. Surface low develops over central WY along strengthening
lee trough and developing weak warm front extending from low into
northern NE. Southeasterly upslope flow will promote 1KJ/kg mean
SBCAPE (per HREF) from the Black Hills into southern SD by mid-
afternoon. Some guidance significant higher, but some lower, so
confidence in moisture return a bit shaky. Afternoon buoyancy
values most uncertain over northeastern WY as afternoon mixing
modulates boundary layer. Forecast hodographs depict significant
lengthening with 45-60kts 0-6km bulk shear by evening over much of
the CWA. Hodograph shapes initially suggest splitting supercell
potential with right movers dominant by evening near surface
boundaries. CAMS suggest convective initiation around 19z over
northeastern WY, spreading into the Black Hills/southern SD by
mid-afternoon. Large/very large hail and damaging winds possible
with an isolated tornado near surface boundaries. Some guidance
suggests a secondary round of strong/severe convection as main
synoptic forcing arrives later this evening, but atmosphere will
be worked over. Beneficial rains welcome, however. Temperatures
should be near guidance.

Coolish/unsettled Independence Day foreseen as shortwave spins
across the eastern Dakotas leaving moist/cyclonic flow over the
area. Popcorn showers/thunderstorms likely, but not necessarily an
all-day rain with subsidence/drying ramping up Thursday evening.
Temperatures will be near/slightly below guidance given expected
clouds/precipitation.

Friday through Sunday, western CONUS upper ridge promotes slowly
amplifying thermal ridge over the northern plains. Northwest flow
aloft portends small pops as a couple of inevitable waves wiggle
through the northern Plains per northwest flow.

Next week, confidence is increasing that large scale upper/thermal
ridge will dominate with increasingly dry/hot weather developing.
Probability of MaxT >= 90F 25-50% in the west Wednesday increasing
to 50-75% most areas by Friday.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1006 PM MDT Tue Jul 2 2024

Storms and showers will be in the area mainly Wednesday afternoon
and evening and may cause intermittent MVFR/IFR conditions.
Outside of storms, expect VFR conditions.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Dye