Marine Weather and Tide Forecast for Rapid City, SD

DISCUSSION
(Today Through Sunday)
Issued at 203 AM MDT Mon May 12 2025

07z surface analysis had trough from western ND into eastern WY.
Water vapour loop had weakening upper ridge from the Midwest into the southwest CONUS and upper trough/low coming onshore via WA/OR.
Leftover weak returns per regional radar loop over the CWA, but most echoes virga. Disposition of the upper trough/low the main forecast concern.

Today/tonight, upper trough moves into the northern Rockies. Cold front develops ahead of it with deep southwest flow over the CWA, which will maintain/slightly increase low level thermal ridge.
EFI continues to show MaxT today in the 90-100th percentile which translates to another day of record highs. 100F isn't out of the question east of the Black Hills toward central SD. Lower tropospheric kinematic fields don't look as favorable for wind advisory speeds (HRRR <20% chance 45mph gusts) as they did yesterday for south-central SD, so will hold off on headlines. Dry air/cap should prevent PoPs.

Tuesday, upper trough slowly moves eastward as cold front reaches the western half of the CWA and then stalls per parallel flow aloft. Ensemble guidance gives 70s behind the front and 80s/lower 90s ahead of it, but confidence near the front on the lower side given uncertainty in eventual position. It still looks too dry/capped for daytime PoPs, but increasing moisture/QG-forcing ahead of upper trough will move into the CWA Tuesday night with increasing chances for showers/thunderstorms.

Wednesday/Thursday, upper trough rotates through the northern Plains with deepening surface low ahead of it and developing gusty northwest winds, especially Thursday (50-90% chance >45mph gusts)
when headlines may be needed. Ensembles show main forcing/QPF has shifted a bit northwest with the highest QPF from northeast WY into far northwest SD. NBM continues to show a south-north gradient of chance for >0.50" 48-hour QPF of 30-70%. Entire CWA is painted by 70-100% chance >0.1" QPF. Temperatures will be significantly modulated by amount of clouds/QPF duration, so confidence not particularly high for actual values but eventually will end up below normal by Thursday.

Friday through Sunday, weakly unsettled weather foreseen given progressive upper flow and embedded wiggles. More significant upper trough arrives for early next week with the potential for beneficial QPF and maybe some snow for some folks.

AVIATION
(For the 12Z TAFS Through 12Z Tuesday Morning)
Issued At 525 AM MDT Mon May 12 2025

VFR conditions will prevail through the period. Gusty south/southwest winds are expected through this evening, especially east of the Black Hills toward south-central South Dakota.

FIRE WEATHER
Issued At 203 AM MDT Mon May 12 2025

Minimum relative humidities today will be 10-20% with deeply mixed boundary layer supporting gusty south/southwest winds, especially in the afternoon/early evening. Temperatures/low relative humidities will be tempered Tuesday, but still elevated east of the Black Hills. Thus, elevated/near critical fire weather conditions continue today and then Tuesday ahead of the cold front. Locally critical conditions may occur where fuels are still receptive, but green up is here per land manager input/GOES-19 NDVI remote sensing.

Upper trough moves through Tuesday night through Thursday with increasing chances for wetting rains, gusty northwest winds, lower temperatures, and higher relative humidities. Unsettled weather continues through the end of the forecast with perhaps a more impactful system for early next week.

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