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646
FXUS63 KUNR 151051
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
451 AM MDT Sat Jun 15 2024

.KEY MESSAGES...

- Isolated showers/storms continue early this morning, with more
  thunderstorms moving in this afternoon. Some storms later today
  may be severe.

- Hot temperatures continue today, but a cold front late tonight
  will cool things off moving into next week.

- Active weather continues for much of next week, with cooler
  temperatures and near daily chances for showers and storms.

&&

.DISCUSSION...
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(Today Through Friday)
Issued at 142 AM MDT Sat Jun 15 2024

Current Water Vapor and upper air analysis shows mild ridging over
the northern and central plains, with upper trough over the great
lakes region, and an upper low entering into the NW PAC region.
Surface analysis shows low over the western ND/SD border, with
warm frontal boundary over western SD this morning. Currently
radar has elevated showers over northwestern SD as well as south
central SD. Winds are light and variable with temps generally in
the 60s.

A complex setup will lead to an interesting weekend ahead. Today
will be a hot one, with highs in the mid 80s to mid 90s prior to
a stronger cold front going through the region late tonight.
Southerly moist flow at the low levels will allow for dew points
in the low to mid 60s, especially for areas east of the Black
Hills. Pre-frontal surface trough moving through the area will
help generate showers and storms again as early as noon, but
likely mid-afternoon. Increasing CAPE through the day will lead
to severe potential in the late afternoon and evening timeframe.
Widespread ML CAPE values of 500-1500 j/Kg are expected, while
better CAPE east of the Black Hills could climb into the 2000-2500
j/Kg range. Modest shear (30-40kts) in the early afternoon will
also increase later in the day. Best chance for severe storms
today will be from northeastern WY to northwestern SD, however
enough instability elsewhere that cant rule out severe storms for
other areas of western SD. Cold front enters northeastern WY later
this evening and treks through the rest of the forecast area
overnight. 4 to 6 mb/3hr pressure rises behind the front may
result in advisory level winds for a few hours overnight. DESI
currently shows 50 to 80 percent chance of advisory level winds
just east of the Black Hills for a 2-3 hour period overnight
behind the front.

Cooler temperatures move in behind the front, with highs ranging
in the upper 60s to 70s across the forecast area Sunday. The PAC
NW upper low treks across southwestern Canada, and southwesterly
flow aloft sets up over the region later Sunday. Near stationary
frontal boundary sets up from southern WY to southern MN late
Sunday night. Coupled with strengthening south to southeast 850mb
flow aloft, setup is good for nocturnal storms over the area.
Given the timing, hail will be the main threat with these storms
Sunday night into Monday morning. PAC NW low over MB slides
northeast early Monday, however secondary wave develops behind it
moving over MT later Monday into Tuesday, increasing chances for
storms/showers again, mainly over northwestern SD. Mid-week looks
mostly dry, though cannot rule out some isolated daytime
convection, with perhaps a slight warming trend towards the end of
next week.
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&&

.AVIATION...
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(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 448 AM MDT Sat Jun 15 2024

Local IFR CIGS due to stratus over south-central SD will dissipate
this morning. Isolated/scattered thunderstorms will develop this
afternoon and persist into the evening hours. The highest
concentration of storms will be over northwest SD. MVFR
conditions expected with the strongest storms, which may contains
gusty, erratic winds and hail. A fast-moving cold front will slice
through the area after 04z, bringing localized gusts around
40kts, especially just east/northeast of the Black Hills.
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&&

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

$$

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