Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 202313
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
513 PM MDT Sun May 20 2018

.DISCUSSION...(This Evening Through Sunday)
Issued at 150 PM MDT Sun May 20 2018

Water vapor imagery shows an upper low currently over north central
Nebraska/southeastern South Dakota, a ridge building over the
central Rockies, and a trough deepening along the California coast.
At the surface, high pressure is located across central South
Dakota, with a lee trough beginning to form along the Bighorns. A
few high clouds remain across the area, with temperatures at 20Z
ranging from the lower 50s in the hills to the mid 60s on the
plains. Gusty southeasterly winds of 15 to 20 mph are common
across northeastern Wyoming, with lighter southeasterly winds of 5
to 15 mph across western South Dakota.

The upper low will continue to weaken as it slowly drifts north
through southeastern South Dakota tonight. At the surface, the lee
trough will continue to deepen, keeping breezy conditions across
northeastern Wyoming.

The upper ridge over the Rockies will continue to build while the
axis slowly shift east across the CWA by late Monday/Monday
night. This will create southwest flow over the area by Tuesday.
Warm air associated with the upper ridge will allow for above
average temperatures Monday, and especially on Tuesday. The upper
level southwest flow, will bring additional moisture into the
northern plains. Meanwhile, the trough over the California coast
will cut-off and slowly meander over the desert southwest, before
getting caught up in flow and lifting north into Canada by the
end of the week. Energy ejecting from the upper low, will bring a
few weak disturbances through the area Tuesday through Thursday.
Moderate MLCAPE and marginal 0-6km bulk shear will combine to
perhaps bring a strong TSRA to the CWA Tuesday afternoon/evening
and then again on Wednesday afternoon/evening.

On Thursday, the upper low is in Canada and moves eastward, bringing
an weak upper trough through the area. A few storms are possible,
but most of the energy will be east of the CWA.

For Friday and Saturday, The upper ridge will once again build over
the Rockies with the axis centered over the forecast area on Sunday.
This will bring drier air to the region and warmer temperatures for
most of the holiday weekend.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 512 PM MDT Sun May 20 2018

Conditions will be VFR through the period. Breezy SE winds can be
expected over NE WY tonight. ISOLD TS will be possible over NE WY
and the northern Black Hills Monday afternoon.

&&

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

$$

DISCUSSION...MLS
AVIATION...JC


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