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364
FXUS63 KUNR 161049
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
449 AM MDT Sun Jun 16 2024

.KEY MESSAGES...

- Cold front passing through early this morning, with strong
  northwest winds behind the front.

- Nocturnal storms expected tonight into Monday morning. Some
  storms could be severe.

- More storms possible later Monday, with some severe potential
  again.

&&

.DISCUSSION...
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(Today Through Saturday)
Issued at 135 AM MDT Sun Jun 16 2024

Current surface analysis shows cold frontal boundary passing
through the forecast area early this morning. At the upper levels,
southwest flow is setting up aloft, with a mild disturbance over
western SD. Radar shows light showers/storms generating over the
western ND/SD border, moving northeast into ND, otherwise clear.
Temperatures out ahead of the boundary sit in the mid 60s to low
70s, while behind the front areas are dropping into the upper 50s
this morning.

Strong pressure rises behind the cold front will allow for gusty
northwest winds for a brief time this morning, with gusts 50 to 65
mph possible over much of the western SD plains area. Wind
advisory and High Warning are in effect for the overnight hours,
but should be done by 6am at the latest. Temperatures will be
much cooler behind the cold front today, with highs ranging from
the upper 60s over the Black Hills, to around 80 in south central
SD. Shortwave energy makes its way across the northern plains
later tonight. Coupled with increasing 850mb theta-e advection and
stronger 0-6km shear, expecting some nocturnal storms to develop
along a frontal boundary stretching from southwest of the forecast
area up into MN. MU CAPE values overnight climb into the 1500-2500
j/Kg range. Main threat will be large hail with these late night
elevated storms. CAMS do show some secondary developments further
north in our forecast area, but main severe threat will range from
southwestern SD to central SD where the better forcing and shear
sets up.

An even cooler day is expected for Monday, with low level
northeasterly flow over the region. Highs stay in the 60s for much
of the forecast area, with south central SD being the exception
in the mid 70s. Another wave makes its way over the northern
plains later Monday, allowing for potential redevelopment of
showers/storms. Storm development will be conditional though, as
models show a stratus deck across much of the region that may
limit potential energy. How fast the clouds clear out Monday will
determine if storms are able to develop, as well as severe
potential. NAM shows stratus deck lingering long enough to
potentially hamper any storm development, while the GFS clears out
clouds closer to central and south central SD, allowing for
increasing CAPE and storm potential. If storms are able to fire
up, main threats with this later Monday disturbance will be both
hail and strong winds, but cannot rule out a tornado with the
better low level helicity near the boundary.

Progressing towards mid-week, upper level PAC NW trough swings
across the Rockies and over MT/ND around Wednesday. Some isolated
showers/storms may be possible the middle of the week, however
mostly dry conditions can be expected. Better chance for
precipitation comes closer to the weekend, as temperatures warm
back up and a mid-level wave rides up the southwesterly flow.
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&&

.AVIATION...
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(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 447 AM MDT Sun Jun 16 2024

Gusty northwest winds (20-35kts) on the western SD plains will
quickly subside this morning. VFR conditions expected through 03z
Monday. Isolated/scattered thunderstorms will develop after 02z
Monday with MVFR conditions in the strongest storms. In addition,
IFR CIGS due to stratus may develop near the SD/NE border after
06z Monday.
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&&

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

$$

DISCUSSION/KEY MESSAGES...Dye
AVIATION...Helgeson