Area Forecast Discussion
Issued by NWS Rapid City, SD

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033
FXUS63 KUNR 130525
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1025 PM MST Tue Dec 12 2017

.UPDATE...
Issued at 1020 PM MST Tue Dec 12 2017

Deep low moving through eastern North Dakota with cold front
into western South Dakota. Already getting wind gusts over 50 mph
on the plains of western South Dakota. Overall, forecast moving
through with gusts of 50+ mph.

&&

VFR conditions are expected through Wednesday. Cold front will
move through the area tonight
.DISCUSSION...(This Evening Through Tuesday)
Issued at 236 PM MST Tue Dec 12 2017

Upper level analysis has highly amplified flow with a trof across
the East Coast, and large ridge across the western CONUS. Strong
upper shortwave is currently just topping the ridge across
Alberta. Skies are mostly clear across SD, with some smoke in the
southern Black Hills and along the eastern foothills. At the
surface, low pressure is located across south central Canada, with
the warm front through the eastern Dakotas. Temperatures at 2pm are
very mild, in the 50s and low 60s, and winds are out of the west
at 10 to 20 mph.

Another fast-moving shortwave will push through the Northern
Plains tonight. Models remain in good agreement with this system,
which looks very similar to the one Sunday night/Monday morning.
CONSMOS is showing advisory criteria winds for much of the western
SD plains, but NAM and GFS forecast soundings are showing 50+ kt
winds mixing down again, especially just east of the Black Hills.
This is supported by another 5-6 mb pressure difference over the
Hills with 40-50 kt boundary layer winds. The strongest winds are
expected to be after midnight into early Wednesday morning with
the strongest CAA and pressure rises. A High Wind Warning is in
effect from Sturgis to Rapid City and areas just east of the
Black Hills. A Wind Advisory is in effect for the rest of the SD
plains from late tonight through late Wednesday afternoon. Highs
Wednesday will be cooler, in the 40s.

Yet another shortwave will cross the region Wednesday night into
Thursday morning, bringing a reinforcing shot of cold air and gusty
winds. Winds on Thursday don`t look quite as strong as
tonight/Wednesday; however, a little more moisture is associated
with this system, bringing a chance for some light snow. Highs
Thursday will be mainly in the 30s.

The upper ridge axis will shift over the region Friday, as a
stronger wave moves over the Pacific Northwest. Highs Friday will
warm back into the 50s, but chances for precip will increase Friday
night into Saturday as the wave crosses the Rockies. Highs this
weekend look to be in the upper 30s to upper 40s.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1020 PM MST Tue Dec 12 2017

VFR conditions expected through Wednesday. Strong northwest winds
will spread across the area behind a cold front with gusts of
40-50kt over the South Dakota plains. The winds will diminish
Wednesday afternoon.

&&

.FIRE WEATHER...A strong cold front will move through the Black
Hills area late this evening. Northwest winds across the southern
Black Hills will increase around midnight to 20 to 25 mph with
gusts to 35 mph. These winds will persist through Wednesday
morning, then begin to slowly decrease by late morning to early
afternoon. Temperatures will be cooler on Wednesday, with highs
only in the lower 40s. Minimum afternoon RHs will fall to around
30 to 35 percent across the southern Black Hills.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 3 AM MST /4 AM CST/ to 3 PM MST /4 PM CST/
     Wednesday for SDZ042>044-046-047-049.

     Wind Advisory until 3 PM MST Wednesday for SDZ001-002-012>014-
     025-030-032-074.

     High Wind Warning until noon MST Wednesday for SDZ026-031-072-
     073.

     Wind Advisory from noon to 3 PM MST Wednesday for SDZ026-031-072-
     073.

WY...None.
&&

$$

Update...7
DISCUSSION...15
AVIATION...7



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