Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201701

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1101 AM MDT Tue Jun 20 2017

Issued at 945 AM MDT Tue Jun 20 2017

Current surface analysis shows cold front sagging slowly south
across northwest into central SD, with high pressure centered over
northwest ND. Upper level analysis continues to show high pressure
centered over eastern AZ, with ridging to the north across the
intermountain west. Northwest flow aloft is in place across the
Northern Plains. Skies are mostly cloudy to the north of the
front across northwest SD, with clear to partly cloudy skies
elsewhere. KUDX radar showing a few sprinkles possibly reaching
the ground in the Lemmon area. Temps are in the upper 60s and 70s
with light winds in most areas, except for some breezy conditions
over in the Gillette area.

A warm day is on tap for much of the area as the front stalls near
the Black Hills and then begins to move back to the north and east
as a warm front later this afternoon and tonight. Highs will be
in the 80s to around 90 degrees. A few of the short range
convective models are showing the potential for an isolated shower
or thunderstorm this afternoon from far northeast WY to the Black
Hills near the front. Will put in a slight chance for the Bear
Lodge Mts into parts of the northern Black Hills area for later
this afternoon. Will watch to see if these chances may need to be
expanded. Otherwise, the better chances for activity should hold
off until this evening when main shortwave energy and cold front
approach the area. Shower and thunderstorm chances will increase
across northeast WY this evening and spread east across much of
the area overnight. Southerly low level jet will strengthen
overnight across central SD, with modest theta-e advection over
central into eastern SD. Could see a stronger storm or two over
western areas in the evening, then possibly a strong storm later
tonight to the east of the Black Hills, near the nose of the low
level jet.


.DISCUSSION...(Today Through Monday)
Issued at 307 AM MDT Tue Jun 20 2017

Upper level analysis has broad trof across the eastern CONUS and a
ridge building across the western CONUS. In between, fast
northwest flow continues across the far northern Plains. Skies are
currently mostly clear across the Dakotas. At the surface, high
pressure resides across the area with temperatures at 3am in the
50s to lower 60s.

Today...Upper level ridge will shift into the northern Plains
today as surface high pressure slides southeast into western
Minnesota. Light winds this morning will become east to southeast
across the SD plains by this afternoon. A weak surface trof will
slide across eastern WY, with light winds becoming westerly by the
afternoon. Some cloud cover will work its way into the area from
Montana through the day. But until then, mostly sunny skies will
prevail, allowing temperatures to rise into the 80s across the
area, with a few locations flirting with 90 degrees.

Tonight...Upper ridge will start to flatten as a shortwave slides
across the Rockies and crosses the area. This shortwave looks like
it will initiate some showers and storms across western portions
of WY late this afternoon, with that convection shifting east into
northeast WY for the evening hours. Showers and storms will
continue east across the Black Hills area around midnight, and
into central portions of SD after midnight. As the showers and
storms move east of the Black Hills, some better mid level
instability could produce a few stronger storms, with some
marginally severe hail possible from the Philip area into far
south central SD. These storms should shift east of the forecast
area by very early Wednesday morning.

Wednesday...Upper ridging flattens a bit more across the northern
Plains as a strong shortwave slides across southern Canada. Highs
will remain warm, with readings in the 80s to lower 90s again.
Northwest winds across the SD plains will be a bit breezy at 10 to
25 mph, highest across northwest SD. By Wednesday night, trailing
mid level boundary combined with the low level jet/strong warm
advection should produce another round of nocturnal convection
across western SD, shifting east through the night. Once again, a
few storms could produce some hail near severe limits overnight
into early Thursday morning.

Thursday...A cooler day is on tap as a broad upper trof develops
over the northern CONUS. High temperatures will be around 10
degrees cooler than Wednesday, with readings in the 70s to around
80 degrees. After the morning convection across central SD shifts
east, partly to mostly sunny skies are expected across the area.
Northwest winds may still be a bit breezy across far northwest SD.

Friday into the weekend...A stronger shortwave system will slide
southeast across the Northern Plains, bringing colder air yet,
along with a better chance for showers and a few thunderstorms
into Saturday. Cool air will be in place for much of the weekend,
with highs in the 60s and 70s and lows mostly in the 40s. Looks
like warmer air will build back into the region early next week.


.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1059 AM MDT Tue Jun 20 2017

VFR conditions are expected through this afternoon. A few
thunderstorms with MVFR conditions will be possible this evening
and overnight.




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