Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 181126

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
526 AM MDT Thu May 18 2017

.DISCUSSION...(Today Through Wednesday)
Issued at 330 AM MDT Thu May 18 2017

Current surface analysis shows main area of low pressure across
southeast CO, with inverted trough stretching back northwestward
to a secondary low pressure area over central WY. Fairly strong
high pressure in place across south central Canada. Upper level
analysis shows weakening low moving rapidly northeast into the
western Great Lakes region, with main low drifting slowly
southeast across UT. Most of the forecast area is dry for the time
being, with some showers over mainly Campbell County WY right now
as some moisture wraps northwestward around the low over UT.
Skies are mainly cloudy, with some clearing across far northwest
SD. Temps are mostly in the low to mid 40s, with some 30s across
the Black Hills. Winds are from the north-northeast, breezy at
times across northwest SD.

Unsettled weather of late will continue late this week, with chilly
and wet weather for many areas later today through Friday. Medium
range models in pretty good agreement on timing of track of upper
low as it moves slowly into CO later today and tonight, then ejects
northeast into the Central and Northern Plains late Friday into
Saturday. Still some timing and track differences between the
models, which will ultimately affect how much pcpn the forecast area
receives, especially southern portions of the CWA.

Chance for rain will increase from the southwest later this morning,
and especially this afternoon, as strong energy to the northeast of
the low rotates north into northeast WY and southwest SD. Some
decent rainfall amounts are likely across southern parts of
northeast WY and far southwest SD this afternoon into this evening,
quarter to half an inch with some higher amounts likely. Amounts
will taper off to the north and east of these areas. It will be
another chilly day for most areas, with highs ranging from the 40s
over northeast WY, the Black Hills, and far southwest SD to the mid
to upper 50s from northwest to south central SD where dry conditions
will persist through most or all of the day. This wave will weaken
tonight as it moves into drier airmass to the north, but still
expecting good chances for pcpn tonight from southern parts of
northeast WY to the Black Hills and through southern SD as
additional energy pushes north into these areas. Temps will drop
into the 30s across the Black Hills this evening and across much of
northeast WY overnight. Rain will likely mix with and change over to
snow in some areas, especially the higher elevations of the Black
Hills and northeast WY. Some accumulations look likely Thursday
night into Friday, up to a few inches across the higher elevations
of the Black Hills and up to a couple of inches over southern
Campbell County. Could even see a mix at times early Friday down to
the surrounding plains of the Black Hills, including the Rapid City

Showers and areas of rain will continue on Friday over much of the
area, with the focus shifting more toward southwest into central SD.
Some light snow is still likely over the Black Hills. Friday will be
the chilliest day, with highs in the 40s across the plains, 30s over
the Black Hills. Bulk of heavier pcpn will shift east of the area
late Friday and Friday night as the low picks up speed and moves
across NE into central or eastern SD by Saturday morning. Rain and
snow showers will persist Friday night into Saturday morning,
especially for areas east of the BH. Could see at least some patchy
frost in areas Saturday morning, especially if skies were to begin
to clear out over western areas.

After lingering showers exit on Saturday, the rest of the weekend
looks to be dry with a warming trend into Sunday. A few showers are
possible late Sunday into Sunday night over parts of northeast WY as
the next system approaches. Northwest flow aloft will be dominant
across the region next week as large trough covers the eastern half
of the country. A series of disturbances will bring periodic chances
for showers and a few thunderstorms. The best chances at this time
look to be Monday and Wednesday. Temps early next week look to be
slightly below average with breezy conditions likely during the
late morning and afternoon hours.


.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 522 AM MDT Thu May 18 2017

MVFR cigs, with some IFR conditions around the Blkhls, will
persist this morning across most areas. Some improvement expected
this afternoon, with conditions then deteriorating again tonight.
Rain will spread north into the area today, especially near/south
of I-90. Rain will mix with snow tonight across nern WY and the
Blkhls with IFR vsby.




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