Area Forecast Discussion
Issued by NWS Rapid City, SD

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247
FXUS63 KUNR 191137 CCA
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
534 AM MDT Fri May 19 2017

.DISCUSSION...(Today Through Thursday)
Issued at 234 AM MDT Fri May 19 2017

Water vapor shows massive upper low over over wrn CO with
moisture being pulled north out of the srn plains through the nrn
plains. At the surface, high pressure located over nrn ND with
ridge extending swwd into nern WY is stifling the nrn extent of
pcpn across our cwfa. Radar return shows best area of pcpn across
west central SD at this time, although some of the higher returns
are bright banding. Early morning Thermal profiles and webcams
show the snow level around 4000 feet in the Blkhls although not
much has accumulated there. Best accumulations have been across
srn Campbell county with the latest report around 5 inches in
Wright.

Upper low expected to drift slowly ewd through CO today. Pcpn
expected to continue for much of the cwfa this morning, although
nwrn SD will likely see little pcpn given aforementioned surface
ridge. Dry slot showing up on water vapor from cntrl NEB in swrn
SD will likely keep pcpn amounts on the light side this morning
for our area, with pcpn chances then diminishing by the afternoon.
Additional snow accumulations should be rather light across nern
WY into the Blkhls. Will leave the winter wx advisory in place for
srn Campbell county and reevaluate around 6 am to see if it can
expire or needs to be extended.

Best chances for pcpn by tonight will then shift into scntrl SD
as next wave is ejected nwd.

Stacked low then expected to lift newd through the cntrl plains on
Saturday and into the upper midwest Saturday night. Best chances
for pcpn will be in our far ern zones, although some
convergence/instability pcpn possible around the Blkhls.

Warmer conditions expected on Sunday, with some aftn -shra
possible given nw flow aloft. Better chance for -shra on Monday as
strong upper wave embedded in the nw flow crosses the nrn plains.

Low pcpn chances continue early in the week, before upper ridge
builds into the Rockies and dry us out through mid week. Pcpn
chance may return by the end of the week once sw flow aloft
returns. Cool conditions Monday and Tuesday will be replaced by
warmer conditions mid to late week.

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 234 AM MDT Fri May 19 2017

VFR conditions will prevail over northwest SD through Friday
afternoon save for local MVFR conditions in precipitation. Areas
MVFR/IFR conditions over northeast WY through south central SD
will deteriorate to a good deal of IFR conditions due to lower
CIGS and -RA. Some LIFR conditions are expected near the Black
Hills and over northeast WY south of KGCC where rain has mixed
with or changed to snow. Precipitation will taper by Friday
morning, but should redevelop by Friday afternoon across southern
SD.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 524 AM MDT Fri May 19 2017

Mainly VFR conditions will prevail over northwest through south
central SD through Saturday morning save for local MVFR
conditions in light precipitation. Areas of MVFR/IFR conditions
will persist through the afternoon over northeast WY and southwest
South Dakota due to lower CIGS and -RA. Some local LIFR
conditions are expected across the higher elevations of the Black
Hills and over northeast WY south of KGCC with low visibilities
and CIGS with snow. Precipitation will begin to taper off this
afternoon and early evening with conditions slowly improving
overnight.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...Winter Weather Advisory until 6 AM MDT early this morning for
     WYZ055.

&&

$$

DISCUSSION...Johnson
AVIATION...15



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