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000
FXUS63 KUNR 151621
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1021 AM MDT Tue Aug 15 2017

.UPDATE...
Issued at 1021 AM MDT Tue Aug 15 2017

Current surface analysis shows low pressure over far southwest SD,
with warm front extending east-southeast across far northern NE
and cool front south and west of the area. Upper level analysis
shows low pressure across southwest SK, with upper trough
extending south across the Northern Rockies into the eastern Great
Basin. KUDX radar shows scattered to numerous showers across a
good portion of the western and south central SD plains, with
some thunder in a few spots. Activity over northeast WY and the
Black Hills is more isolated at this time. Temps are in the 60s
and lower 70s with variable winds.

Have updated mainly to make some adjustments to the pcpn chances
for the late morning and early afternoon based on latest models
and radar trends. The best chances for pcpn through midday will
generally be across northwest SD, with the better chances
generally from the Black Hills to south central SD in the
afternoon. The threat for severe storms across our area still
looks greatest near the surface low as it tracks across far southern
SD/northern NE. MLCAPE values southeast of the Black Hills are
progged to be in the 1000 to 1500 j/kg range later this afternoon
with favorable shear, especially toward south central SD. Hail and
strong wind gusts will be the main threats from any severe storms.
Timing for the severe storm threat will generally be from
early/mid afternoon through early evening. Also made some minor
adjustments to temps and sky cover for the rest of today.

&&

.DISCUSSION...(Today Through Monday)
Issued at 340 AM MDT Tue Aug 15 2017

Upper level analysis has large trof across the western CONUS, with
several shortwaves lifting through the Great Basin and northern
Plains. Skies are cloudy across the area with showers and isolated
thunderstorms ongoing. At the surface, Low pressure was located
across the Nebraska panhandle with a weak trof extending north
into eastern Montana. Temperatures at 3am were in the upper 50s to
mid 60s, with light southerly winds.

Good chances for showers and isolated storms will continue today
into tonight as shortwave trough moves across the Rockies and into
the Plains. Area of low pressure and associated frontal boundary
will slide slowly east along the SD/NE border today, with the
best instability this afternoon into this evening across southern
SD into NE. The best chance for a few strong to severe storms will
be southeast of the Black Hills and especially near the low
pressure area along the NE border. With abundant moisture, a few
storms could produce very heavy rainfall. Highs will only be in
the upper 60s and 70s with a good deal of showers and cloud cover
in most areas. Main shower activity will exit from west to east
tonight, with a few showers possibly lingering across south
central SD into early Wednesday morning.

The rest of the week and the weekend look drier and warmer as weak
ridging and drier westerly flow will be in place across the
region. Highs will be back to near average levels Thursday through
the weekend. A few afternoon and evening thunderstorms will be
possible on Thursday, and again on Monday.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 519 AM MDT Tue Aug 15 2017

Scattered to numerous SHRA/TSRA will continue through this evening
with MVFR CIGS/VSBYS. Local IFR conditions with the strongest
storms. After 04z, expect mostly VFR conditions with leftover
local MVFR CIGS possible given moist boundary layer.

&&

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

$$

Update...26
DISCUSSION...15
AVIATION...Helgeson