Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 211104
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
404 AM MST Tue Feb 21 2017

.SHORT TERM...(Today Through Wednesday Night)
Issued at 404 AM MST Tue Feb 21 2017

Current surface analysis shows low pressure along the north
central MT and Canadian border, with warm front extending
southeast into the western Dakotas. Upper level analysis shows
fast near zonal flow over the region, with weak ridging over the
Northern Plains. Cutoff upper low over the Southern Plains is
moving slowly eastward. Temps are very mild again this morning,
mostly 40s and 50s, with some high clouds passing overhead.

A strong west-southwest low level jet is in place over the area this
morning, combined with a tightening pressure gradient behind the
warm front, is producing strong winds at times over warmer areas of
northeast WY and the Black Hills area. A few gusts to over 50 mph
have been noted in some of these areas overnight. Though the low
level jet will dissipate later this morning, gusty winds will
continue at times today as deep boundary layer mixing develops and
taps into higher winds aloft. Breezy to windy conditions expected
elsewhere across the forecast area, especially late morning and
afternoon. We are looking at some record highs across the area again
today, with highs in the mid 60s to mid 70s across the plains, upper
50s and 60s across the Black Hills. Downtown Rapid City record high
is 68 and should be broken, while RAP airport record of 74 will be
more difficult to reach.

Low pressure and trailing cold front will approach the area this
evening. Embedded shortwave energy aloft will accompany the front
and bring a chance for showers across mainly northeast WY and the
Black Hills area, though a few showers may make it across the
western SD plains overnight. Winds will stay gusty in some areas
this evening, then diminish overnight. Lows will be in the 30s and
40s.

Cooler weather returns Wednesday, though still above average levels,
with highs in the mid 40s to upper 50s. Warmest conditions will be
to the south and east of the Black Hills. A few showers are possible
across northern SD, especially near the ND border, as shortwave
energy passes mostly to the north of the region. Long wave trough
will dig south and east across the Pacific NW Wednesday night, with
southwest flow developing across the Rockies into the high plains.
Chances for rain and snow will increase Wednesday night, especially
late, across northeast WY into southwest SD. Onset of pcpn looks to
be a bit slower with latest model runs. A light accumulation of snow
is possible over portions of northeast WY into far southwest SD by
daybreak. Lows will be in the upper 20s and lower 30s.

.LONG TERM...(Thursday Through Monday)
Issued at 404 AM MST Tue Feb 21 2017

Latest model comparison for late week storm system shows better
agreement between the models on overall evolution of system, but
still some track and timing differences with regard to heavier
snowfall potential. The 00Z GFS and EC came in a bit further north
with the track than previous runs, while the NAM is the furthest
south of the group. All have kept the trend of a weaker upper
level feature/open trough crossing the region. 00Z GEM is now
weaker and further south, coming into better line with the EC and
GFS. They all show the surface low developing and tracking well
south of the region, across southern KS and into the upper
midwest. General blend of the EC, GFS, and NAM now show the
heaviest snowfall potential mostly across southeast WY and NE
Thursday and Thursday night, but the northern edge of some heavier
snowfall could clip far southern portions of northeast WY and far
southern SD, especially if the more northerly solutions end up
correct. The snowfall projections at this time would suggest
little to no snowfall across much of northwest SD, with up to a
few inches near and along the Interstate 90 corridor including
most of the Black Hills, and some potential still for around 6
inches of total snowfall from early Thursday through early Friday
across far southern SD and into southern portions of northeast WY.
Timing for bulk of snowfall would be Thursday morning through
Thursday evening, with some lingering light snow into Friday
morning, especially over southern portions of the CWA. With the
surface low tracking so far to the south, winds should not be much
of an issue with this system.

The rest of the long term will be much colder, with near to slightly
below average temperatures through the weekend and into early next
week. Highs will mostly be in the upper 20s and 30s. West-northwest
flow will be mostly dry this weekend and Monday, but weak
disturbances could bring a few snow showers at times, especially
across the Black Hills and into far northeast WY.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 404 AM MST Tue Feb 21 2017

VFR conditions are expected through the forecast period.
Gusty west to southwest winds can be expected at times across
northeast WY and far western SD today. The strongest winds are
forecast to be across northeast WY through the early afternoon. A
passing cold front tonight will bring a chance for mostly rain
showers across northeast WY and the Black Hills area.

&&

.FIRE WEATHER...
Issued At 404 AM MST Tue Feb 21 2017

Warm temperatures and gusty winds later today will result in very
high to extreme grassland fire danger across a good portion of
the west and south central South Dakota plains. Relative
humidities will drop to 20 to 25 percent across most of the
plains.

.HYDROLOGY...
Issued at 404 AM MST Tue Feb 21 2017

Ice jams continue along portions of the White River from the
Interior area to the Missouri River. Minor flooding has been noted
along the White River near White River, as well as further west
near Interior. Flooding is expected to remain minor, affecting
some agricultural land along the river, over the next day or two.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 5 PM MST this afternoon for SDZ025-026-072-
     074.

WY...High Wind Warning until 5 PM MST this afternoon for WYZ054-055-
     058.

&&

$$

SHORT TERM...26
LONG TERM...26
AVIATION...26
FIRE WEATHER...26
HYDROLOGY...26



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