518
FXUS63 KUNR 060352
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
952 PM MDT Thu Jun 5 2025

.KEY MESSAGES...

- Chances for showers and thunderstorms through Saturday night.
- Warmer and drier conditions early next week.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 238 PM MDT Thu Jun 5 2025

Upper level analysis has a positively tilted upper trough
extending from northwestern Ontario down through Manitoba,
Montana, Idaho and into northern California, creating west
northwest flow across the forecast area. Water vapor satellite
shows a disturbance exiting the forecast area currently, with
additional waves in southwest Wyoming, northern Utah, southern
Idaho and northwestern Montana. At the surface, a trough is
pushing through south central South Dakota which is associated
with the current disturbance as another trough extends from
Nevada, through northern Utah into southwestern Wyoming and an
additional trough is associated with the shortwave in western
Montana into Idaho. Radar loop at 21Z shows a large area of rain
showers across most of the forecast area.

For tonight, the current shortwave will continue to exit the area
to the east, allowing the showers and isolated thunderstorms to
end. As skies clear and winds subside, expect some fog to develop
after midnight, especially where the recent rain fell. Thus, have
added some areas of fog to the forecast.

For Friday, fog should burn off by 14Z. The next shortwave swings
through the northern Rockies into the central Plains. Best
forcing and shear remain southwest of the forecast area, but ML
CAPE of 250-500 J/kg may allow some showers and thunderstorms
across northeastern Wyoming and the Black Hills.

For Saturday/Saturday night, a weak wave will move through the
area in northwest flow as an upper low strengthens over southern
Canada. A cold front pushes through the forecast area beginning
around 15Z. Behind the front, breezy/windy northwest winds are
expected, especially across the western South Dakota plains.
Showers and a few thunderstorms are possible behind the front
through Sunday night.

On Sunday, the windy northwest winds will continue with highs
slightly cooler but still seasonable.

The upper ridge builds early in the week, with 850 temps around
25C by Wednesday. As the ridge shifts east into the High Plains,
the flow becomes southwest, which could lead to more active
summertime weather conditions.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 952 PM MDT Thu Jun 5 2025

In the wake of afternoon/evening showers, areas of BR/FG are
developing over the western/central SD plains and far
northeastern WY. MVFR to localized LIFR conditions have already
materialized, with these conditions expected to expand through the
night. Dense fog and accompanying VLIFR conditions may develop
over portions of the west central SD plains by 09z and persist for
several hours. Most significant reductions to vsbys are expected
to remain east of KRAP, and upper-level clouds arriving from the
west may disrupt fog disruption entirely in and around the TAF
site. However, a brief period of LIFR conditions cannot be ruled
out.

Improvement to VFR conditions is expected area-wide by around 15z,
but additional SHRA/TSRA may lead to reduced cigs/vsbys again
tomorrow morning and afternoon.

&&

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

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...Sherburn