057
FXUS63 KUNR 021107
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
507 AM MDT Tue Jul 2 2024

.KEY MESSAGES...

- Organized severe thunderstorms possible Wednesday
- Coolish 4th of July
- Warming (and probably drier) pattern starts Friday

&&

.DISCUSSION...(Today Through Monday)
Issued at 147 AM MDT Tue Jul 2 2024

07z surface analysis had cool front from the eastern Dakotas into
southern WY, which then wrapped northwest into lee trough from
central MT into central WY. Water vapour loop had mean upper
trough from AB/SK into western WY with embedded shortwave emerging
from southern ID. Regional radar loop depicted increasing returns
ahead of wave as it interacts with surface features. This will be
the main weather feature for today.

Today, shortwave moves through southern WY into northern NE. Most
guidance depicts cluster of showers/TS scooting across southern
half of CWA with PoPs quickly decreasing northward. Weak buoyancy
expected with decent 0-6km bulk shear. Probabilities of organized
strong/severe thunderstorms is low today. Temperatures will be
tricky with cloud cover/precipitation modulating morning
temperatures downward, but afternoon solar insolation may be
sufficient for most places to reach guidance.

Tonight, subsidence behind shortwave will promote mostly dry and
seasonally cool temperatures.

Wednesday, shortwave drops out of Canada into the northern Plains
pushing lee trough/frontal boundary into the Black Hills. Return
flow ahead of it brings tongue of 1KJ/kg+ SBCAPE from the Black
Hills into far southern SD. 0-6km bulk shear around 45kts. Joint
probabilities (SBCAPE > 500J/kg, SBCIN < 25J/kg, 0-6km bulk shear
>30kts) 50%+ for these locations, reflected in SPC Day 2 outlook.
CAMS suggest early start to strong/severe convection, perhaps by
19z with supercells initially. Large (very large) hail, damaging
winds main threat, but a tornado cannot be ruled out near the dry
line/surface boundary in far southwestern SD. Temperatures will be
near guidance.

Wednesday night/Independence Day looks unsettled and cool as
upper trough spins through the northern Plains bringing cold pool
aloft and showers/TS. How wet/cool is not clear given ensemble
guidance, but the weather should improve later in the day/evening
for planned outdoor activities.

Looking ahead, upper ridge over the western CONUS whisks thermal
ridge into the area. However, proximity to northwest flow from
central Canada into the Midwest could promote the intrusion of a
couple of fronts/waves and convective chances. Odds are overall, it
will be warmer/drier for Friday through early next week.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 505 AM MDT Tue Jul 2 2024

Isolated to scattered thunderstorms are possible across northeast
Wyoming and western South Dakota this morning through the evening
hours. The best chance of thunderstorms will be from the central
Black Hills southeastward into southern and south-central SD.
Expect storm chances to taper off after 23-02z this evening.
Outside of thunderstorms, VFR conditions will prevail through the
forecast period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...SE