423
FXUS63 KUNR 262330
AFDUNR

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

.DISCUSSION...(This Evening Through Monday)
Issued at 238 PM 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
mostly clear across the CWA with the exception of some high clouds
moving across far western SD. At the surface, high pressure is
located across the eastern Dakotas, with east to southeast return
flow across the area. Temperatures at 3 PM are in the 70s to lower
80s.

Tonight...Upper ridge axis will shift into the northern Plains
overnight, as surface high moves into the upper midwest. Surface
low will deepen across eastern Montana, tightening the pressure
gradient across the area. Winds will become breezier overnight,
keeping lows in the 50s to lower 60s.

Tuesday will be hot, with highs in the mid 80s to mid 90s, as the
thermal ridge shifts over the area. Very gusty southerly winds
will continue, especially across southern SD. These strong winds
will advect in warm, moist air, resulting in dew points in the low
to mid 50s across the SD plains. Further west, a dry line will
push into far southwest SD by early afternoon. With temperatures
in the 90s, and dewpoints dropping into the low 40s, relative
humidities will fall into the teens to around 20 percent. The dry
air combined with breezy winds may produce critical fire weather
conditions for a few hours in the afternoon across far southwest
SD.

The upper ridge will break down during the afternoon as a wave
pushes into the region, and convection will initiate across the
Black Hills and 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 northeast WY and
western SD later Tuesday evening and overnight.

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 00Z TAFS Through 00Z Tuesday Evening)
Issued At 527 PM MDT Mon Jun 26 2017

VFR conditions are expected through tonight. A southerly low
level jet developing this evening will bring some low level wind
shear to Northeast WY and western SD late this evening and through
the night. A cold front will settle into the region Tues,
bringing veering winds and eventually sct SHRA/TS late
afternoon/evening.

&&

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

$$

DISCUSSION...15
AVIATION...JC