442
FXUS63 KUNR 140402
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1002 PM MDT Thu Aug 13 2026

.KEY MESSAGES...

- An active pattern will bring unsettled conditions at least
  through the weekend, with daily chances for thunderstorms.

- Temperatures will generally be near average through the end of
  the week into early next week.

&&

.UPDATE...
Issued at 950 PM MDT Thu Aug 13 2026

03Z surface analysis shows troughing over southeastern MT this
evening, another disturbance behind it over Idaho with a frontal
boundary snaking into Wyoming and Colorado. Radar shows showers
over eastern Wyoming and southeastern MT moving northeast
synoptically with the disturbance. Precipitation will remain in
the overnight hours as the wave slides eastward.

Very little change to the overall forecast this evening. Have made
some minor tweaks to PoPs and QPF over the next 24 hours as hi-res
models update and based off current observations. Patchy areas of
fog may occur overnight given the moist air and light winds.
Another disturbance still progged to move through the area
tomorrow, continuing the trend of scattered showers over the area.
Severe weather is not expected.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 208 PM MDT Thu Aug 13 2026

Water vapor imagery shows broad upper ridging centered across south
SE CONUS with the main axis stretching through the Midwest. Moist,
active southwesterly flow continues across the western CONUS...all
the way back to a trough near the West Coast. Several shortwaves
are crossing northern High Plains to the central/northern
Rockies. The nearest wave is pushing through central/eastern WY
through the NE WY zones south into the CYS CWA. As the wave
continues NE, showers and thunderstorms will push further into
western SD while weakening. Weak CAPE and shear will damper any
severe weather potential today. The next (much stronger) wave will
bring continued chances of elevated convection late this evening
and into the overnight hours. These showers could generally
produce up to half an inch of QPF by 12z. Active weather will
continue through Friday with additional shortwaves bringing
mid-level forcing. Models show a surface low strengthening
tomorrow near the ND/MT line with a cold front pushing through NE
WY and far western SD. Good Theta E advection across NW/Central
SD ahead of the front will support SBCAPE nearing 2000 J/kg. While
shear is not impressive, could still see pulsing isolated
strong/severe storms Friday afternoon and early evening, with
large hail as the main threat. Active weather and near average
temperatures will continue through weekend into the first half of
next week, with daily chances for showers and thunderstorms.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1001 PM MDT Thu Aug 13 2026

Scattered showers will be possible across the forecast area
overnight. MVFR to IFR conditions are expected tonight across the
area as moist southeast upslope flow continues. Fog may develop
overnight across the Black Hills and areas south of I-90 before
burning off Friday morning.

&&

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

$$

UPDATE...Dye
DISCUSSION...13
AVIATION...Dye