Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 261709

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1109 AM MDT Mon Jun 26 2017

.DISCUSSION...(Today Through Sunday)
Issued at 142 AM MDT Mon Jun 26 2017

Upper analysis shows a large ridge over the western CONUS, with a
90 kt jet over the northern plains in northwest flow. Skies are
clear across the CWA. With a surface high over the Dakotas, winds
are light and variable. Temperatures at 2 AM are in the mid 40s
to mid 50s.

Another warm and dry day is expected, as the upper ridge shifts over
the Rockies. Highs will be in the mid 70s to the mid 80s, and
minimum relative humidity values will be 15-20% across northeastern
WY. Southerly winds will be around 10 to 15 mph. Winds will become
breezier overnight as the pressure gradient tightens, keeping lows
in the 50s to lower 60s.

Tuesday will be hot, with highs around 90, as the thermal ridge
shifts over the area. Gusty southerly winds will continue,
especially across south central SD. These strong winds will advect
in warm, moist air, resulting in dew points in the 50s. Models vary
on their ML CAPE forecasts for Tuesday afternoon, but about 1500 to
2000 J/kg is expected across western SD by 18Z. The upper ridge will
break down Tuesday as a wave pushes into the region, and convection
will initiate across western SD during the afternoon. With 0-6 km
shear around 40 kts, supercells will be possible. The trough will
quickly push into the eastern Dakotas, and most of the activity will
also shift east into central SD by early evening. However, some
additional storms will possible across western SD with the cold
front later Tuesday evening.

The active pattern will keep chances for thunderstorms in the
forecast through the end of the week, but instability is weak to
marginal compared to Tuesday. The next main wave is progged to move
through Thursday. Highs will be in the 70s and 80s, and lows will be
in the 50s.


.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1104 AM MDT Mon Jun 26 2017

VFR conditions are expected through tonight. A low level jet
developing this evening ahead of an approaching cold front may
bring some low level wind shear to Northeast WY and western SD
late this evening and through the night.




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