Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 241728
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1128 AM MDT Mon Apr 24 2017

.UPDATE...
Issued at 948 AM MDT Mon Apr 24 2017

Current surface analysis shows frontal boundary from northeast WY
through southern SD, with colder air pushing south into northern
and eastern portions of the forecast area. Upper level analysis
shows low pressure over the Pacific NW, with trough digging south
and east across the western US. Skies are mostly cloudy along and
behind the front with some fog noted, especially along the
northern and eastern foothills of the Black Hills and adjacent
plains. Fog should generally lift by midday. Partly cloudy skies
noted over much of northeast WY into southwest SD. KUDX radar
showing isolated showers over south central SD. Current temps
range from the 30s over northwest SD to around 50 over far
southern SD and southern parts of northeast WY. North-northwest
winds are brisk behind the front over the SD plains.

A good deal of clouds will hang around the SD plains today, with
clouds increasing into the afternoon over northeast WY and
southwest SD. Chances for showers will increase this afternoon
across northeast WY and the Black Hills as upper level energy
approaches. A thunderstorm or two is possible by late
afternoon/early evening over northeast WY and possibly the Black
Hills. Have updated grids to lower temps a few degrees in most
areas, especially north and east of the Black Hills. May need to
lower them more through the day, especially over northern and
eastern areas, and will update as needed. Lowered pops a bit over
northeast WY and the Black Hills, at least through early
afternoon, with the better chances expected late. Some minor
adjustments were also made to cloud cover and winds.

&&

.SHORT TERM...(Today Through Tuesday Night)
Issued at 425 AM MDT Mon Apr 24 2017

Upper level analysis has broad ridge across the eastern CONUS with
broad trof across the west. Closed low is currently spinning just
off the coast of Washington and a weak shortwave is lifting
northeast across the Dakotas. Skies are mostly cloudy across the
Northern Plains. At the surface, low pressure is located across
eastern Colorado, with an inverted trof extending northeast
through south central South Dakota, and a cold front draped across
Northeast Wyoming into southwest South Dakota. Temperatures at 3am
are in the 30s across northwest SD, and in the 40s elsewhere.
Winds are mainly out of the north.

Today...Upper flow remains southwesterly as west coast trof moves
into the Pacific Northwest. A brief break in precip is expected
today as the area remains between waves. Temperatures will remain
mild, with highs in the 50s and 60s...coolest across northwest SD
where morning fog and persistent low clouds will hang in for much
of the morning. Chances for showers and isolated thunderstorms
returns late this afternoon across Northeast Wyoming and far
western SD, spreading eastward overnight. A potent compact
shortwave is progged to move into Northeast WY after midnight
tonight, bringing significant precipitation to the area. Colder
air will be pulled in from the north, and rain will mix with and
likely change to snow overnight in many areas. Models have
continued the trend for colder temperatures aloft, giving parts of
the CWA the potential for some significant snows. Have hoisted a
Winter Storm Watch for late tonight and Tuesday across Northeast
Wyoming and the Black Hills for the potential of 6 inches or more
of heavy wet snow.

Tuesday...Rain and snow will continue across the area through the
afternoon, with precip diminishing Tuesday evening. Precip will
likely remain all snow for much of Northeast Wyoming and parts of
western SD through the event. Some accumulating snow of lesser
amounts is expected on the plains, with some melting during the
daytime hours as it reaches the ground. High temperatures are only
expected to be in the low 30s where precip is the heaviest, with
some 40s possible across northwest SD and far south central SD.

Precip will begin to clear out Tuesday evening with cold
temperatures expected Tuesday night. Lows will fall into the 20s
across the area, with some teens possible in low lying or snow
covered areas.

.LONG TERM...(Wednesday Through Sunday)
Issued at 425 AM MDT Mon Apr 24 2017

Cool and unsettled weather will continue for the rest of the week
and into the weekend. The next significant low pressure system to
affect the region will begin moving in Thursday night, bringing
another round of rain and snow. ECMWF and GFS are currently
showing the upper low sinking south over the Four Corners region
by Saturday morning, and then slowly sliding northeastward across
the central plains during the weekend. This could bring a long
duration of rain/snow to the area, depending on the track and
timing of the system. Below average highs in the 40s and 50s are
expected into next weekend.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1124 AM MDT Mon Apr 24 2017

MVFR to local IFR cigs will trend to VFR at many places this
afternoon. SHRA (ISOLD TS) will spread into nern WY later this
aftn and far wrn SD tonight, with rain changing to snow late.
Expect widespread IFR/LIFR conditions to develop with the pcpn,
especially once it begins to snow later tonight. Lowest conds
expected over NE WY and in/around the Black Hills.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from late tonight through Tuesday afternoon
     for SDZ024-028-029.

WY...Winter Storm Watch from late tonight through Tuesday afternoon
     for WYZ054>058.

&&

$$

Update...26
SHORT TERM...15
LONG TERM...15
AVIATION...JC



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