334
FXUS63 KUNR 190527
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1127 PM MDT Fri Sep 18 2026

.KEY MESSAGES...

- Cool and wet this weekend, with daily precipitation in the
  region.

- Gradual warmup early next week.

&&

.UPDATE...
Issued at 935 PM MDT Fri Sep 18 2026

The evening update to the forecast utilized latest radar and
satellite imagery and latest hi-res model guidance to show a
diminishing trend in the PoP field overnight, before PoPS increase
again Saturday afternoon into Saturday night.

Latest radar imagery shows a line of rain showers and
thundershowers tracking eastward while fading out. Earlier, this
line of storms produced wind gusts around 40 to 55 mph, heavy
rain, and frequent lightning. Early rainfall reports range mainly from
about a quarter inch to half inch with a few isolated stations up
to three-quarters of an inch. Rain is still falling so final
reports are expected Saturday morning.

Beginning Saturday afternoon, no changes were made to the
inherited forecast. Widespread precipitation is expected Saturday
into Sunday as the upper low tracks towards the area. Drier and
warmer weather is still expected next week.

&&

.DISCUSSION...(This Evening Through Friday)
Issued at 213 PM MDT Fri Sep 18 2026

Current Water Vapor and upper air models show southwest flow over
the forecast area, as upper low digs into the Rockies. 18Z surface
analysis depicts a low over southeastern SD, with frontal boundary
stretching into central Nebraska. Winds are generally light out of
the north, with temperatures in the 60s to upper 70s.

Out ahead of the upper low, a disturbance will lift up into the
region this evening. The line of showers/storms is currently in
central Wyoming moving northeast, expected to enter the forecast
area in a few hours. Generally light precipitation with the
evening precipitation, but accumulations nearing a tenth of an
inch may be possible in heavier precip cores. Precipitation may
linger into the overnight hours, and some showery development is
possible again during the day Saturday. There`s a low-end chance
for a severe storm Saturday afternoon, given some CAPE values
500-1000 j/Kb, however weak effective shear (20-30kts).

Attention then turns to the main event, as the upper low moves
over Wyoming later Saturday into Sunday. Widespread precipitation
is expected to move into the region over this timeframe. Heaviest
amounts are expected Sunday morning and afternoon and will taper
off from west to east Sunday night into Monday. LREF probabilities
for 24 QPF 0.5" or more has a bullseye of 70-90% over the Black
Hills into southwestern SD. Probabilities for 1" or more QPF range
from 30-60% in the same area. Expect cooler temperatures as well
as the low moves into the plains, with high temperatures Sunday
only reaching around 60 over the plains, and the low to mid 50s
over the Black Hills.

By the latter half of monday, the pattern changes again as upper
ridging builds over the plains, bringing a gradual warming trend
Monday through much of next week. Temperatures climb back to at or
above normal by Tuesday and Wednesday.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1125 PM MDT Fri Sep 18 2026

Showers will continue eastward overnight, likely dissipating over
the next few hours. IFR/LIFR CIGS will return to the western SD
plains late tonight and continue through Saturday morning. Areas
of dense fog are also expected with LIFR VSBY. CIGS could see some
gradual improvement through the day tomorrow but should still be
limited to no higher than MVFR, especially as showers and
thunderstorms redevelop during the afternoon and evening hours.

&&

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

$$

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