Rapid City, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

876
FXUS63 KUNR 071122
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
522 AM MDT Thu Aug 7 2025

.KEY MESSAGES...

- Hot today with heat indices 100-105F south-central SD
- Marginal to slight (level 1-2 of 5) risk of severe
  thunderstorms tonight and Friday afternoon/evening
- Seasonally drier for the weekend into next week

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 144 AM MDT Thu Aug 7 2025

07z surface analysis had low over KBYG, which was along a frontal
boundary from western ND into ID. Modest low level jet (KUDX
radar had 30kts just off the surface) impinging on frontal
boundary with ACCAS/isolated TS over southeast MT. This elevated
convection may affect far northwest SD early this morning.
Nighttime microphysics loop depicted blossoming stratus/fog over
parts of NE, which will creep into the far southern reaches of
the CWA indicative of the soupy atmosphere that will blanket the
eastern reaches of the CWA today. Widening our view, water vapour
loop had southwest flow over the CWA in response to upper trough
slipping southeast into the northwest CONUS from southwest Canada.
Effect of this system the main forecast concern.

Today through Friday, upper trough moves through the northern
plains. WY surface low will deepen some as it combines with
southwest flow aloft to create deep boundary layer mixing and
strong push of dry air today. Dry line will surge into parts of
northeastern WY/southwestern SD with plummeting dew points behind
it. Thermal ridge peaks pushing temperatures well into the 90s
with some 100s from southwest into central SD likely (HREF >80%
chance). Sticky Td/s in the mid 60s to lower 70s will combine with
forecast MaxT to create 100-105F heat indices (HREF >80% chance)
over central SD leading to the issuance of a Heat Advisory this
afternoon/early evening. Shifting our gaze further north shows
strong buoyancy/moderate shear by tonight, but with significant
SBCIN. Surface based convection chances not zero, but not looking
great. However, support is much higher into ND with the potential
for convection to slip into far northwest SD tonight with
resultant damaging wind/large hail threat along outflow or
outflow-induced convection. A smattering of CAMs support. As
surface low shifts east tonight, trailing cold front will move
into the CWA, exiting the area later Friday. Front may be
convectively enhanced with gusty northerly winds late tonight.
Cold front will become focus for strong/severe convection Friday
afternoon/evening, but with highest threat east of the CWA. Post-
frontal environment will be characterized by weak
buoyancy/moderate shear and little SBCIN, which may be conducive
to isolated severe thunderstorms. Temperatures today will be near
guidance, especially where dry air prevails. Temperatures Friday
will be tricky with cold front modulating readings, so confidence
is lower.

For the weekend into next week, northwest flow aloft becomes
westerly. Drier air will be in place, but it is August so while
PoPs will drop off, we`ll probably have some isolated convection
in/near the CWA through the period. Temperatures will be
seasonally warm.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 520 AM MDT Thu Aug 7 2025

IFR stratus/patchy fog over south-central to western SD to far
northeastern WY will quickly burn off this morning. TSRA may occur
tonight, especially over northwest SD where local IFR conditions
are expected with any storm.

&&

.FIRE WEATHER...
Issued At 144 AM MDT Thu Aug 7 2025

Deep boundary layer mixing will promote the development of very
dry air (HREF >80% chance <15% MinRH) over the far southwest
reaches of the CWA this afternoon along with gusty west/southwest
winds at times. Best combination of MinRH/gusty winds will extend
from Wright, WY to KIEN. Collaboration with land mangers
yesterday indicate fuels over parts of the CWA are now critical.
Thus, will upgrade Fire Weather Watch to Red Flag Warning where
fuels/meteorological conditions warrant.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from noon MDT /1 PM CDT/ today to 7 PM MDT /8 PM
     CDT/ this evening for SDZ014-032-043-046-047-049-077.
     Red Flag Warning from noon today to 8 PM MDT this evening for
     SDZ322.
WY...Red Flag Warning from noon today to 8 PM MDT this evening for
     WYZ315.
&&

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Helgeson
FIRE WEATHER...Helgeson