927 
FXUS63 KUNR 201527
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
927 AM MDT Wed Aug 20 2025

.KEY MESSAGES...

- Hot and dry today through most of Thursday, with near-critical
  to locally critical fire weather conditions anticipated over
  portions of the area.

- Unsettled conditions return late this week as temperatures
  moderate behind a front.

&&

.UPDATE...
Issued at 927 AM MDT Wed Aug 20 2025

Slightly warmer temperatures and higher dew points are anticipated
this afternoon through early evening, particularly in and around
river valleys across western/central SD. This may result in more 
widespread 100F+ apparent temperatures beginning around midday 
and continuing through late afternoon. As such, opted to 
introduce a heat advisory to account for much of the northwestern
and west central/south central SD plains.

Rest of forecast remains on track. Will monitor daytime warming,
drying, and mixing to assess potential expansion of the heat
advisory, along with fire weather concerns.

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 343 AM MDT Wed Aug 20 2025

Upper level ridge axis stretches across the Northern Plains today
with attendant low level thermal ridge developing over the CWA. 
Afternoon temperatures will climb into the upper 90s to low 100s 
across most of the CWA with highs in the upper 80s across the 
higher elevations of the Black Hills. The drier airmass should 
keep heat indices from reaching criteria level (100F) in most 
spots precluding issuance of a heat advisory at this time. That 
being said, some spots in the eastern third of our CWA could see 
heat indices in the triple digits this afternoon. The hot, dry, 
and breezy conditions will also lead to fire weather concerns, 
will elaborate further in the Fire Weather Discussion.

Upper low over Canada scrapes by the region with attendant sfc 
trof/cool front pushing through the CWA during the day Thursday. 
This should push the hottest temperatures to south central SD with
the rest of the CWA being in the 80s to low 90s. In terms of the 
potential for storms, there will be a strong cap in place thanks 
to the warm 850mb-700mb temps. So while we could see a few showers
and storms along the front as it passes through, not anticipating
any widespread convection and severe potential appears to be 
limited at this time as better deep layer shear lags behind the 
front. Highs on Friday will be 10-20 degrees cooler, staying in 
the mid 70s to 80s across much of the region with temperatures 
cooling off further through the weekend as a trof digs into the 
eastern half of the US and northwest flow develops over the 
region. In terms of precipitation chances, positioning of the low-
level baroclinic zone and large-scale ascent will keep chances for
precip to our south with the southwestern half of the CWA seeing 
the best chances for showers/storms over the weekend.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Thursday Morning)
Issued At 445 AM MDT Wed Aug 20 2025

VFR conditions are expected for the forecast period. Southerly
winds will increase through the day today with gusts of up to 30
kt possible across northwestern SD.

&&

.FIRE WEATHER...
Issued At 343 AM MDT Wed Aug 20 2025

Near critical fire wx conditions are expected across much of the 
area today. Temperatures this afternoon will climb into the upper 
90s to low 100s with minimum RHs at or below 20% across much of 
western SD into northeastern WY. Northeastern WY into southwestern
SD could see critically low RH values (15% or lower) with breezy 
southerly winds developing through the afternoon hours. Lowest RH 
values and strongest winds won't overlap considerably in time and 
space, so will hold off on issuing any fire weather headlines. 
However, locally critical fire wx conditions are possible this 
afternoon, especially across northeastern WY into southwestern SD.

Elevated to near critical fire wx conditions are possible again 
on Thursday as a cold front pushes through the region. Winds will 
shift to the northwest through the day Thursday with gusts of 
25-30 mph. Temperatures Thursday will still be hot, in the 80s to 
near 100, with minimum RH values in the 25-45% range.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 7 PM MDT /8 PM CDT/ this evening for SDZ001-
     002-012>014-031-032-043-046-049-073-077-078.
WY...None.
&&

$$

UPDATE...Sherburn
DISCUSSION/KEY MESSAGES...Wong
AVIATION...Wong
FIRE WEATHER...Wong