922
FXUS63 KUNR 032321
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
521 PM MDT Thu Jul 3 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms expected for Friday with
  heavy rain possible.

- More unsettled weather expected Saturday with possible severe
  storms as stronger wave pushes through the area.

-Next week will see periodic chances for storms with continued
 above normal temps.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 154 PM MDT Thu Jul 3 2025

Current water vapor imagery shows 500hpa ridge firmly entrenched
across the middle of the CONUS with wave topping the ridge in ND.
Ill defined waves are moving to the northeast in the sw flow on
the backside of the 500hpa ridge. At the surface, weak low
pressure is located in southeast MT with an E-W oriented boundary
along with ND/SD border with a trailing trough to the south just
to the west of Campbell Co, WY.

The 500hpa ridge axis if forecast to shift east of the CWA this
evening and overnight, putting the CWA into a SW flow regime
aloft. The lead wave moves over NE Wyoming, nrn Black Hills and NW
South Dakota this evening. Trailing surface trough mentioned
prior will also aid in convective development. 0-6km bulk shear
values arent the best for widespread severe weather (on the order
of 30 to 35 kts) but some of the stronger storms this evening
could produce some sub-severe hail. Meanwhile very steep low level
lapse rates support the possibility of strong wind gusts.

Thoughts then turn toward Friday. Friday will most likely start
off  cloudy/mo-cloudy based upon low level RH values seen in the
models. Lead 500hpa wave is exiting the cwa with stronger wave
beginning to move into the BH region. Ensembles point toward high
probabilities of sfc dwpts greater than 60 degrees for much of the
plains east of the Black Hills. PWAT values on the order of
1.50-1.75 lean toward the potential of heavy rain with some of
the storms that develop later in the day Friday. Ensembles are
also showing 30-40% probabilities of seeing greater than 30dBz
reflectivities by 18z Friday across the Black Hills and western SD
prairies.

As 500hpa ridge conts to flatten with zonal, westerly flow
developing over the region, periodic disturbances will move
quickly through bringing occasional thunderstorm chances to the
region. The models are highlighting Saturday night as a possible
MCS evening, developing in NE Wyoming and shifting east across
western SD. Stay tuned.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 518 PM MDT Thu Jul 3 2025

VFR conditions expected to prevail through most of the period for
most areas. Scattered -TSRA will develop this evening, mainly
over northeastern WY/far western SD and move across the western
third overnight. Winds will shift to the northwest tonight as a
cold 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...Hintz
AVIATION...JC