Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 171123
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
523 AM MDT Mon Apr 17 2017

.SHORT TERM...(Today Through Tuesday Night)
Issued at 305 AM MDT Mon Apr 17 2017

Current surface analysis shows cold front slowly sliding south
across southern SD and northeast WY, with high pressure in place
over the Canadian Prairie provinces. Upper level analysis shows
trough finally moving east of the region, with shortwave ridge
moving into the Northern Plains. Strong shortwave is moving
quickly east-northeast across the Pacific NW. Skies are mostly
clear at this time, with some high cloudiness increasing over
western portions of the CWA. Temps range from 20s across far
northwest SD and the Black Hills to the lower 40s across south
central SD. Winds are mostly light and variable.

Unsettled weather will return for a good portion of the upcoming
week as fast and near zonal flow brings a series of systems across
the northern and central Plains. Shortwave to the west will move
into the northern high plains later this afternoon. Cold front will
slide south of the area early this morning and then shift back to
the north and east as a warm front when low pressure with the
shortwave system moves east across northern WY/southern MT this
afternoon. Highs will range from the lower 60s across far northwest
SD and the higher BH to the mid 70s over far southwest SD. Winds
will become south to southeast ahead of approaching low, increasing
through the late morning and afternoon. The strongest winds will be
from northeast WY into northwest SD, where gusts to around 40 mph
are likely.

Chances for showers and storms will increase toward mid-late
afternoon as front lifts north and interacts with approaching upper
level energy. Most of the shorter range models are not showing much
in the way of pcpn before 22-23z, mostly due to relatively strong
cap in most areas until stronger energy arrives. The best chances
later this afternoon may end up being from far northeast WY into far
southwest SD near developing weak trough/dryline. Will keep lower
pops from northeast WY into the Black Hills area for mostly mid to
late afternoon. MUCAPE of around 1000 j/kg will develop in the
afternoon/early evening across southwest SD, high enough for a few
strong to possibly severe storms if they develop. Shear would also
be sufficient for at least short-lived supercells. The main threats
from any stronger storms would be hail and gusty winds. Shortwave
and low pressure will move quickly across the region tonight, with
the best chances for pcpn to the east of the Black Hills this
evening, likely toward northwest into central SD. Activity will exit
eastern portions of the CWA late this evening and into the
overnight.

Mild temperatures will continue on Tuesday as shortwave ridge slides
across ahead of the next system. Highs will be in the 60s and lower
70s. A few showers and thunderstorms are possible late in the day
from northeast WY to the Black Hills. The better chances for rain
will arrive Tuesday evening with the next shortwave system and
spread east across the forecast area overnight.

.LONG TERM...(Wednesday Through Sunday)
Issued at 305 AM MDT Mon Apr 17 2017

Rain and showers will continue on Wednesday, with decent pcpn
amounts expected in some areas by the time the system exits
Wednesday evening. Pcpn amounts of close to an inch or a bit more
are possible from the Black Hills area into parts of the SD
plains. Some snow accumulation is possible across the highest
elevations of the Black Hills Wednesday morning. Cool conditions
on Wednesday, with highs in the 40s and lower 50s.

A brief break from pcpn is expected on Thursday before the next
system digs southeast from the Northern Rockies to the Central
Plains Thursday night and Friday. The medium range models have
started to track this system a bit further north as it moves across
the region, so pops have been expanded further north and east and
also raised across northeast WY into southwest SD for later Thursday
night and Friday. The unsettled weather could last into at least the
early part of the weekend as weak shortwave energy passes across on
the back side of the system. Temperatures late in the week will
mostly be near average, with possibly a bit of a warmup toward
Sunday.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Tuesday Morning)
Issued At 519 AM MDT Mon Apr 17 2017

Gusty southeast winds will develop over northeast Wyoming and
western South Dakota this morning and continue into this
afternoon. Winds will shift to the west-northwest this evening.
Area of MVFR ceilings will spread into southwest South Dakota this
morning, with ceilings increasing to VFR by late morning. Showers
and thunderstorms will move from west to east across the area
this afternoon into tonight. Local IFR conditions expected with
the thunderstorms.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

SHORT TERM...26
LONG TERM...26
AVIATION...7



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