512
FXUS63 KUNR 172022
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
222 PM MDT Mon Jun 17 2024

.KEY MESSAGES...

- Re-development of showers and storms, some storms may be
  strong to severe.

- Below normal temperatures continue for much of the week, warming
  up towards the weekend.


&&

.DISCUSSION...(This Evening Through Monday)
Issued at 134 PM MDT Mon Jun 17 2024

With the upper trough, currently located over Idaho and western
Montana, approaching from the west, fast southwesterly flow
aloft continues over the forecast area this afternoon. With the
surface low over srn WY/nrn CO, cool, moist easterly flow has
covered most of the forecast area with low stratus today, keeping
temperatures down and leading to areas of fog and drizzle along
the eastern slopes of the Black Hills. The cool temperatures have
greatly limited surface based instability over South Dakota
today, however above the boundary layer MUCAPE has risen to
500-1000J/kg. In the relatively cloud free regions of northeastern
Wyoming diurnal heating has caused SBCAPE to range from
500-1500J/kg so far this afternoon.

Shortwave energy is heading northward on the east side of the
upper trough, as indicated by the showers developing off the
mountains near Casper, WY and moving northward. We may see a few
strong to severe thunderstorms, with large hail and gusty winds,
over parts of northeastern Wyoming later this afternoon into the
evening as the instability aloft reaches the area.

While surface based storms are unlikely over western South
Dakota, expect to see expanding coverage of elevated storms this
evening as the low level jet increases to 40-50kts over western
South Dakota. Again there is a possibility for elevated strong to
severe storms. Large hail and locally heavy rain will be the main
threats over western South Dakota, although locally strong gusty
winds will be possible with the strongest storms.

The upper trough will cross the forecast area on Tuesday. With a
band of drier air moving in from the southwest, the best chances
for precipitation on Tuesday will be along the edges, over
northwestern and south central, SD.

Fast southwesterly flow aloft will stick around for the remainder
of the week, with models showing mild disturbances riding the
flow almost daily. This will allow for active weather to continue
into next weekend, though some days precipitation may be very
isolated. Low level flow becomes predominantly out of the south-
southeast mid-week and later, and we can expect a warming trend
towards the weekend.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1042 AM MDT Mon Jun 17 2024

MVFR/areas IFR stratus over western SD plains will continue to
push into far northeastern WY. Late this afternoon into the
evening hours as a cold front moves through, thunderstorms with
local IFR conditions will develop with erratic gusty winds and
hail possible through 06z Tuesday. Behind the cold front, areas of
MVFR stratus will develop overnight.

&&

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

$$

DISCUSSION/KEY MESSAGES...10
AVIATION...Wong