Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 080437
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
937 PM MST Thu Dec 7 2017

.UPDATE...
Issued at 931 PM MST Thu Dec 7 2017

Extended the wind adv east one row of zones given obs and hires
model output. HRRR progs 60-65 knots 2-3 kft agl through early
Fri morning as a jetlet wraps around the Black Hills. This should
support 25-35 mph winds with some gusts over 50 mph. Some ridge
tops in the Black Hills could easily see gusts over 50 mph through
the night. Winds are still expected to slacken later Friday
morning, before increasing again Friday afternoon on the plains.
Ran both wind adv areas through afternoon, although the latest
guidance shows only marginal adv criteria Friday afternoon.

UPDATE Issued at 609 PM MST Thu Dec 7 2017

Upper jet now over the region as the eastern CONUS low has shifted
east. Linked flow with developing Hills induced pressure gradient
(6 mb progged in NAM) will support downward transport of high
momentum air in the northern and eastern foothills. Gusts to
around 50 mph with a few near 60 mph can be expected through the
night. A lull in winds is possible mid-late Friday morning,
before diurnal mixing supports gusty winds once again Friday
afternoon. Have issued a wind adv now through Friday afternoon.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 315 PM MST Thu Dec 7 2017

Current surface analysis shows warm front over central SD, with
milder air building in behind it. Upper level analysis shows broad
trough covering most of the central and eastern US, with high
amplitude ridge along the west coast. Mostly mid and high clouds
cover the area, with partly sunny to mostly cloudy skies. Temps
are mostly in the 30s with breezy west to northwest winds across
portions of northeast WY and northwest SD.

Looks like we will return to our mild pattern of mid to late
November for at least the next week or so as large scale upper
pattern remains fairly stagnant during this time. This will result
in a generally mild, dry, and occasionally windy pattern through the
period.

The warming trend will continue through the weekend as ridge along
the west coast nudges eastward. Highs on Friday will mostly be in
the 40s, with mid 40s to mid 50s Saturday, and 50s to around 60 on
Sunday. Dry weather is expected through the period, though gusty
winds will prevail at times, especially during the PM hours.

A clipper system is progged to slide quickly southeast across the
Northern Plains Sunday night into early Monday, only bringing a
glancing blow of colder air to our area for Monday. At this time, it
looks like the pcpn with the system will stay north and east of the
CWA. We could see winds approaching advisory criteria across at
least portions of the SD plains later Sunday night into Monday.

Model uncertainty increases beyond the day 5 range, especially with
regard to timing and track of weaker disturbances in persistent
northwest flow. At this time, temps look to warm back up well above
average Tuesday, before another clipper system brings some cooler
air sometime midweek.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 422 PM MST Thu Dec 7 2017

VFR conditions expected through Friday with gusty WNW winds.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 5 PM MST Friday for SDZ025-026-031-072-073.

WY...None.
&&

$$

Update...JC
DISCUSSION...26
AVIATION...JC



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