textproduct: Rapid City

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 06Z TAFS Through 06Z Thursday Night) Issued At 1045 PM MDT Wed Jul 16 2025

Drizzle and fog will affect the Black Hills area through the overnight hours, reducing VSBY at times. MVFR/IFR CIGS will persist across the area early this morning, but a gradually improvement is expected through the day on Thursday as drier air slowly moves into the area.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.