Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 270833
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
233 AM MDT Fri Apr 27 2018

.DISCUSSION...(Today Through Thursday)
Issued at 233 AM MDT Fri Apr 27 2018

Our area sits in a region of northwest flow aloft, between an upper-
level ridge extending from the Desert Southwest northward into
British Columbia and a broad, disorganized trough over much of
eastern Canada and the CONUS. Meanwhile, a weak surface trough and
dry cold front extending from a low pressure centered over the Upper
Midwest is pushing southward across the Dakotas. Aside from
scattered cirrus on the western edge of an upper jet over the
Northern Plains and mid-high clouds in the vicinity of the
surface cyclone to our east, skies are generally clear.

Behind the weak front crossing our area, high pressure is progged to
nose into the ern Dakotas through Friday morning, leading to
generally quiescent weather and above normal temps to close the work
week. Warm temperatures will continue into Saturday as the upper-
level ridge axis shifts eastward over our area, bringing 850 mb
temps in the upper 10-25% of sounding-based climatology by 00z
Sunday. Ahead of an approaching upper-level trough, surface pressure
gradient will tighten nicely, allowing for breezy conditions to
develop across much of the area Saturday afternoon.

Above normal temperatures combined with breezy conditions could
provide some fire weather concerns on Saturday afternoon,
particularly if skies remain clear and allow for ample boundary
layer mixing. RHs are forecast to hover in the 15-20% range over
portions of northeast WY, and given model moist biases in these
situations, it is certainly possible that we could see red flag
conditions for a period of time Saturday afternoon. Thus, will
introduce a fire weather watch for Campbell County Saturday
afternoon into the early evening. Similar fire weather conditions
may continue across northeastern WY into Sunday.

As a broad upper trough shifts eastward into the Rockies late
Saturday into Sunday, will likely see an initial shortwave impulse,
along with an attendant surface cyclone and cold front, cross our
area beginning Sunday afternoon. With modest CAPE in place, could
see the development of some high-based showers and thunderstorms.
Moisture concerns west and a warm nose east will temper updraft strength
somewhat, but could see a few strong wind gusts Sunday afternoon
into the evening and again Monday afternoon.

The aforementioned upper-level trough will continue to dig over the
western U.S. into early next week, establishing a fairly active
pattern over the central U.S. Near-to-below normal temperatures with
occasional chances for precipitation can be expected through the
first half of next week.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 937 PM MDT Thu Apr 26 2018

VFR conditions expected through the period.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...Fire Weather Watch from Saturday afternoon through Saturday
     evening for WYZ259-297.

&&

$$

DISCUSSION...Sherburn
AVIATION...JC



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