613
FXUS63 KUNR 200436
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1036 PM MDT Tue Aug 19 2025

.KEY MESSAGES...

- Isolated thunderstorms will continue over the Black Hills and
  surrounding locations through around sunset.

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

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

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 237 PM MDT Tue Aug 19 2025

Water vapor imagery this afternoon depicts a localized,
elongating midlevel vorticity maximum over western SD in the midst
of broader anticyclonic, subsiding flow. Congested cumulus is
evident over the Black Hills and much of northeastern WY via
visible imagery, with day cloud phase RGB indicating some cloud-
top glaciation in spots. Lightning has recently been limited, but
some of the deeper cells have supported brief lightning activity.
Additional cumulus developing over Pine Ridge and near the
Badlands remains relatively small/shallow at this time, so it may
be too little, too late for any substantive shower/storm potential
before daytime heating wanes. However, cannot rule out a shower
or storm there through the afternoon. Otherwise, summer hasn`t
gone anywhere, with afternoon temperatures generally in the 90s
outside of the Black Hills.

Given general rising heights and no clear forcing mechanism to
maintain convection after the loss of daytime heating, any lingering
shower/storm activity is expected to wane quickly around sunset.
Pressure falls/deepening lee troughing over eastern MT and southern
AB/SK combined with a modestly building surface high over the Great
Lakes region will promote strengthening return flow over western
portions of our area tonight into early tomorrow. Continued rising
heights tomorrow and an expansion of a low-to-midlevel thermal ridge
should bring similar to slightly hotter temperatures. Hot, dry low-
level thermal profiles, large-scale subsidence, and limited layers
of buoyancy should mostly preclude shower/storm activity. However,
cannot rule out a storm or two over the Black Hills or approaching
late in the afternoon from the Bighorns. If storms were to develop
over the Bighorns, would be especially concerned about dry
thunderstorms over Campbell County. Though temperatures will be hot,
advisory-criteria apparent temperatures are unlikely across most of
the area due to the dry air mass. Exception may be across our far
east near the Cheyenne/White Rivers, where dew points may remain
elevated.

Surface trough/front crosses the region through the day on Thursday,
directing hottest temperatures into south central SD. Large scale
forcing/Q-vector convergence appears a bit ragged/disorganized, but
increased forcing for ascent as a midlevel trough carves into the
northern extent of the ridge, bringing height falls Thursday
afternoon and evening, may be enough to support shower/storm
activity. Prefrontal deep-layer shear is weak (<25 kt), and post-
front, rapidly diminishing CAPE as milder air spills southward
beneath a lingering cap may limit strong/severe storm potential. For
now, best bet is for general thunderstorms to prevail. Baroclinic
zone remains near the area through the weekend as additional
shortwave disturbances traverse the region in northwest flow aloft.
Positioning of low-level baroclinic zone and large-scale ascent may
keep the bulk of additional precipitation over the weekend over our
southwestern half, if not south of the area entirely. Either way,
milder temperatures look to be a near-certainty given ensemble
consensus.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1036 PM MDT Tue Aug 19 2025

VFR conditions are expected for the rest of the forecast period.
Low level wind shear will be possible tonight through sunrise
across far western SD and northeast WY.

&&

.FIRE WEATHER...
Issued At 237 PM MDT Tue Aug 19 2025

Hot, dry, and breezy conditions are expected tomorrow into
Thursday. Afternoon high temperatures in the mid to upper 90s,
relative humidity values under 20 percent, and increasing
southerly winds with some gusts to around 30 mph could bring near-
critical fire weather conditions to portions of northeastern
Wyoming and far southwestern South Dakota tomorrow. For now, it
does not appear that the lowest relative humidity values and
strongest winds will overlap considerably in time and space, but
we will continue to monitor the potential for critical fire
weather conditions for a period tomorrow afternoon. Continued
hot, but less dry, conditions are anticipated on Thursday.

&&

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

$$

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