735
FXUS63 KUNR 170002
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
602 PM MDT Wed Jul 16 2025

.KEY MESSAGES...

- Unseasonably cool temperatures continue through tomorrow
  morning, with record lows possible.

- More seasonable temperatures with daily chances for
  thunderstorms return late this week into the weekend; strong to
  severe storms cannot be ruled out.

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 1243 PM MDT Wed Jul 16 2025

Water vapor imagery this afternoon shows a trough crossing the
northern Rockies/Plains, contributing to widespread showers/light
rain over much of our area. Associated cold front is now well south
of the region, with northerly/easterly flow contributing to record
cool temperatures for mid-July. Drier air/subsidence is beginning to
overspread the area from west to east.

Upper wave progresses eastward by late afternoon into the evening,
with deep Q-vector divergence overspreading the area in its wake.
Lingering low-level moisture combined with subsidence associated
with the Q-vector divergence should support continued low clouds/fog
over portions of the area through tonight, especially the Black
Hills/foothills. Surface high pressure slowly shifts southeastward
through the region into tonight, with an associated ridge axis
centered near the Missouri River by 06z. As it does so, our
northeastern tier of counties may clear, which would lead to optimal
radiational cooling and potential for low temperatures near 40
degrees. 850 mb temperatures approaching climatological minima per
the NAEFS will also promote chilly temperatures elsewhere despite
overcast skies, with lows falling into the 40s for much of the area
and 30s over higher elevations of the Black Hills.

Ensemble and deterministic guidance is in general agreement in the
development of large-scale zonal flow emerging by Thursday and
continuing through the weekend. Aside from a potential weak low-
level trof passage late Thursday/early Friday that could briefly
knock back temperatures, an expanding low-level thermal ridge from
the Four Corners/Great Basin northeastward through the Plains should
promote gradually warmer conditions, with much more seasonable
temperatures through at least early next week. Deep westerly flow
will favor relatively persistent steep midlevel lapse rates, while
passing, low-amplitude waves will bring occasional increases in deep-
layer flow and shear to support organized convection if local
convergence can overcome capping by elevated mixed layers. Tomorrow,
for example, HREF mean SBCAPE of 1-2 kJ/kg (further enhanced near
the northern Black Hills) and deep-layer bulk shear magnitudes of 40-
50 kt would be more than sufficient to support organized (and
potentially severe) convection if initiation were to occur. Many
days over the coming week may have similar such low
confidence/predictability but potentially locally high-impact
situations.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 553 PM MDT Wed Jul 16 2025

Isolated showers will be possible overnight into Thursday.
Low CIGS will result in widespread MVFR/IFR conditions through
Thursday morning, particularly across the Black Hills area into
NE WY. Areas of fog will reduce VSBY to IFR across these areas,
as well.

&&

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

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...13