211
FXUS63 KUNR 022342
AFDUNR

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

.KEY MESSAGES...

- Thunderstorm chances Wednesday
- Showery/cool conditions possible for Independence day
- Warming for the first part of next week

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 117 PM MDT Tue Jul 2 2024

Currently the surface trough/cool front is sitting on the SD/MN
border with convection firing across E. Neb already. 500Hpa low
conts to spin across Manitoba with weak wave/trof now moving
through ern WY and into the Black Hills region. NLDN lightning
plot shows isold returns with some of the showers/thundershowers
moving through nern WY and NW Neb associated with aforementioned
weak wave and trof. Much stronger wave is now dropping into NW MT
out of BC/AB and this will be the wave that will garner the
attention for Wednesday.

As the 500hpa trof/wave moves across the area for the remainder
of today, still anticipating scattered showers/thunderstorms.
Ensembles are showing sfc based CAPE values less than 500 J/Kg and
0-6km shear AOA 30kts. While not discounting a brief TSRA with
some pea/dime hail...just am not seeing much in the way for severe
storm development for the remainder of the day.

HRRR shows RH values decreasing with subsidence behind exiting wave/trough
overnight...lending credence to a mostly clear/partly cloudy
night with seasonably cool temperatures.

On Wednesday, attention turns to stronger wave rotating through
region...coupled with east/west boundary/cool front located along
the NE/SD border. Ensembles shows SB CAPE values AOA 1k J/Kg with
little if any CIN remaining by 18z, especially across SW SD...but
show a narrow ribbon of 500-1000 J/Kg SB CAPE values lifting
northward along the WY/SD border ahead of the surface trof pushing
east. Mean 0-6 km shear values are sufficient enough (40-50kts)
that an isolated tornado can not be ruled out across SW SD in the
vicinity of the E/W boundary that will be located along the
border.

Wednesday night and Independence Day, the biggest question is how
many lingering clouds with sprinkles/showers remain as region
remains in broad cyclonic flow. 850Hpa and 700Hpa condensation
pressure defs show partly/mostly cloudy conditions through at
least mid-afternoon Thur before drier conditions try to push in
from the west. Ensemble guidance will most likely be a good first
guess for temps and will just need to make game day adjustments as
those periods get closer.

Gazing ahead...500hpa heights dont really begin to recover until
the first part of next week when western US ridge begins to
rebuild. The most active track at this time appears to take most
of the short wave energy south of the region, but the NW flow
regime can be tricky with weak embedded waves/fronts.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 539 PM MDT Tue Jul 2 2024

Isolated showers/storms will be in the area until around
midnight. Brief MVFR conditions may be experienced with these
showers, otherwise expect VFR through the forecast period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Hintz
AVIATION...Dye