Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 280527
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1127 PM MDT Thu Apr 27 2017

.UPDATE...
Issued at 840 PM MDT Thu Apr 27 2017

Compact upper low continues to support an area of rain/snow over
the western zones. Hires models have trended a little higher with
QPF and have bumped snow amounts up. This includes the central
Black Hills, where rain and snow is ongoing. Precip will become
all snow there tonight, with adv amounts expected, esp around the
Hill City area and south. Amounts will drop off to the north. All
the rest in good shape.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 330 PM MDT Thu Apr 27 2017

Current surface analysis shows low pressure centers over central
WY and southeast CO, with frontal boundary stretching between the
two areas. Upper level analysis shows cutoff low remaining over
southwest Canada, with strong jet digging southeastward from the
Pacific NW to the Southern Plains. Strengthening shortwave energy
noted on water vapor imagery across the northern into central
Rockies with circulation developing over eastern WY. Skies are
cloudy or mostly cloudy across northeast WY and southwest SD, with
some sun to the north and east of these areas. Temps are mostly
in the 40s and lower 50s, with some 30s over the higher Black
Hills and portions of northeast WY. KUDX radar showing some
showers across northeast WY into far southwest SD, mixing with
snow in parts of northeast WY. Regional radars showing heavier
bands of pcpn wrapping around developing upper low from south
central MT to central WY to far western Neb.

Storm system still on track to slide down the east slopes of the
Rockies and into the central high plains tonight and Friday. Upper
low will continue to develop over eastern WY tonight, then track
southeast into northeast CO before getting swallowed up later on
Friday by stronger trough and low developing across the Great Basin
and Four Corners area. Latest medium range models still showing some
differences with regard to exact track, as well as eastern and
northern extent of pcpn swath. This forecast will lean more toward
the slightly more consistent EC, which is not much different than
the going forecast, perhaps raising QPF and snowfall amounts a bit
across most of the area. Have decided to add the southern Black
Hills and the southern foothills zones to the winter wx advisory,
where a few inches of snowfall looks likely across at least western
portions of those areas. Rain and snow will expand across northeast
WY and into southwest SD late today and tonight, changing over to
all snow across most of northeast WY and the Black Hills in the
evening, and other areas later tonight. The northeastward extent of
pcpn shield will likely not make it much past the Black Hills to
portions of south central SD late tonight and Friday morning before
shifting back to the southwest. The heaviest pcpn is likely to fall
over the headlined areas from late this evening through mid morning
Friday as best forcing and band of stronger frontogenesis clips the
far southwestern CWA. Pcpn will then gradually taper off in the late
morning and afternoon. Snowfall amounts in southern Campbell County
look to mostly be in the 5 to 9 inch range, with areas south and
west of Wright possibly seeing higher amounts. The advisory area
should see 2 to 5 inches of snow, with locally higher amounts
possible, especially the further south and west across those areas.
Up to 2 or 3 inches of snow is possible across the rest of the Black
Hills into portions of far northeast WY and toward portions of
Oglala Lakota County.

The weekend looks to be dry, but cool, as main trough and low
pressure system move east-northeast across the central and southern
plains and into the upper MS valley by Monday morning. A few showers
could clip far south central SD on the back side of the system
Sunday. Highs will be in the mid 40s to mid 50s Saturday, 50s to
around 60 on Sunday. The first half of next week still looks to be
unsettled with temps slightly below average. Daily chances for
showers are expected, especially for the afternoon and evening
hours, as a series of weak disturbances pass through on the back
side of the exiting trough. Latest longer range models showing a
nice warmup for late week, possibly into the first half of the
weekend as well, as a ridge finally moves over the area.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1123 PM MDT Thu Apr 27 2017

Area of snow and rain across northeastern Wyoming, the Black
Hills area and southwestern South Dakota will continue through
Friday morning. Widespread IFR conds will continue in those
areas through Friday morning...gradually improving to MVFR
conditions on Friday afternoon. Further east across western SD,
conds will vary from IFR near the Black Hills, to low end
VFR/high end MVFR as dry air fights lower CIGS/precip.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 6 PM MDT Friday for SDZ027>029-041.

WY...Winter Storm Warning until 6 PM MDT Friday for WYZ055.

     Winter Weather Advisory until 6 PM MDT Friday for WYZ054-058.

&&

$$

Update...JC
DISCUSSION...26
AVIATION...10


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