Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 232112
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
312 PM MDT Mon Apr 23 2018

.DISCUSSION...(This Evening Through Monday)
Issued at 312 PM MDT Mon Apr 23 2018

Current surface analysis shows low pressure over far northwest
NE, with cold front stretching from north central SD to southeast
WY. Upper level analysis shows compact, but strong, trough over
central MT and western WY. Regional radars show bulk of pcpn
across central MT at this time, with scattered showers extending
south and east across eastern WY into far western SD, and a few
thunderstorms also noted over east-central WY. Clouds are
increasing from the west, with temps ranging from the 30s in the
Gillette area to the upper 60s over southwest and south central
SD. Temps are dropping behind the front.

System to the west will move across the area tonight into Tuesday,
bringing a good amount of moisture to some areas, especially
northwest SD. Much of northwest SD is expected to see a half inch or
more of pcpn, with a few areas possibly seeing an inch or more.
Ahead of the main band of moisture overnight, some showers and
isolated thunderstorms can be expected late this afternoon into the
evening from northeast WY to far western SD as front moves slowly
east and south across the area. Winds will increase behind the
front, becoming rather gusty for several hours from northeast WY to
parts of western SD late today and this evening. The strongest winds
will generally be in the Rapid City area and adjacent plains from
late this evening through early Tuesday. Will issue a wind advisory
in these areas for winds gusting to over 50 mph overnight.

Main band of pcpn will push east across far northeast WY this
evening and into the northern Black Hills and northwest SD late this
evening and overnight. Colder air will eventually turn rain over to
snow tonight. The more significant snowfall should be across the
northern Black Hills, with some upslope enhanced snowfall developing
later tonight. Snowfall totals of 2 to 6 inches are expected,
highest amounts over the favored higher elevations of the Black
Hills. Accumulation of up to a few inches are also expected over
parts of far northeast WY into Butte and Harding Counties,
especially the higher elevations. Have expanded the winter wx
advisory to include these areas as well. The snowfall forecast is
tricky, with a degree or two difference in temperature potentially
making a big difference in snowfall amounts, so would not be
surprised to see higher amounts in some areas and little or none
in others. Pcpn amounts will taper off rather significantly as you
go south across northeast WY and across southwest SD.

Main band of pcpn will shift east-southeast into central SD Tuesday
morning, with a bit of snowfall possible further east across
northwest SD. By Tuesday afternoon, rainfall will mostly be confined
to south central SD, ending there Tuesday evening. Tuesday will be
the coolest day of the week, with highs mostly in the 40s.

The rest of the week looks to be mostly dry and mild as high
amplitude ridge builds over the Rockies region and generally stays
in place through the weekend. A weak disturbance sliding down the
east side of the ridge could bring a few showers Wednesday night
into Thursday morning over northeast WY and the Black Hills and some
cooler air for Thursday. Temps are expected to be well above average
this weekend, with highs mostly in the 70s.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1120 AM MDT Mon Apr 23 2018

Rain will spread across northeast Wyoming and far western South
Dakota this afternoon and across the rest of the area tonight.
Rain will change to snow over portions of northeastern Wyoming,
the Black Hills and northwestern South Dakota late this evening.
Ceilings will lower with the rain this afternoon, with area of
MVFR ceilings in northeast Wyoming and far western South Dakota.
IFR/local LIFR visibility expected with the snow tonight. Slow
improvement from west to east on Tuesday.

There is a slight chance of thunderstorms this afternoon over
parts of northeastern Wyoming and southwest South Dakota. Gusty
northwest winds will be found across the area tonight, with the
strongest winds around the KRAP terminal...with gusts around
45kts.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 9 PM this evening to 9 AM MDT
     Tuesday for SDZ001-012-024-025-072.

     Wind Advisory from 10 PM this evening to 10 AM MDT Tuesday for
     SDZ026-030-031-073.

WY...Winter Weather Advisory from 9 PM this evening to 9 AM MDT
     Tuesday for WYZ056-057-071.

&&

$$

DISCUSSION...26
AVIATION...Johnson



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