653
FXUS63 KUNR 052314
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
514 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 00Z TAFS Through 00Z Friday Evening)
Issued At 514 PM MDT Thu Jun 5 2025

Showers/storms with localized MVFR/IFR conditions should gradually
wind down from west to east through the evening/early overnight
period. In the wake of this activity, areas of BR/FG will likely
develop after 03z, beginning in southwestern and west central SD
and expanding over much of western SD and portions of northeastern
WY by 09z. IFR/LIFR conditions are likely in some areas through
much of the overnight and into early tomorrow morning. Confidence
in BR/FG at KRAP is relatively low, as light downslope winds may
develop over the foothills and plains adjacent to the Black Hills,
which would limit fog potential. Conditions area-wide should
improve in the 13-16z time frame, with VFR conditions prevailing
by around 18z.

&&

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

$$

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