Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201045
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
345 AM MST Mon Feb 20 2017

.SHORT TERM...(Today Through Tuesday Night)
Issued at 345 AM MST Mon Feb 20 2017

Current surface analysis shows weak low pressure over western SD,
with cold front located from central ND to western Neb. Upper
level analysis shows shortwave moving northeast across far eastern
portions of WY and MT into the western Dakotas. Strong upper jet
in place to the east of the shortwave over the Dakotas. KUDX radar
shows band of showers along the frontal boundary from Faith to
Pine Ridge, moving east-northeast. Other light showers are located
near the shortwave axis over far northeast WY to far western SD.
Temps are mostly in the upper 30s and 40s, with some 50s over
south central SD ahead of the front. West-northwest winds are
increasing behind the front, breezy in some areas.

Even with frontal passage this morning, well above average
temperatures will continue for the first half of the week. Some
cooler air will result in highs today in the lower 50s to mid 60s,
warmest from the Rapid City area to south central SD. Shortwave will
quickly move east of the area by late morning, with showers ending.
Brisk west to northwest winds can be expected across much of the
area today, southwesterly over northeast WY. Skies will clear from
west to east through the morning, with mainly sunny skies expected
this afternoon.

Mild temperatures for tonight as warm air advection returns and low
level jet strengthens over the area. Breezy and gusty west-southwest
winds can be expected, especially from northeast WY through the
Black Hills. Very warm conditions for Tuesday as thermal ridge
pushes north into the area. Highs will be in the mid 60s to mid 70s
across much of the plains, warmest to the south and east of the
Black Hills, especially south central SD. Some record highs are
likely, including Rapid City, where record February highs could be
within reach. Breezy to windy conditions can be expected in most
areas, especially over northeast WY, where some gusts to 50 mph are
possible over southern areas. Next shortwave and cold front will
cross the area Tuesday night, with showers possible from northeast
WY to the Black Hills area.

.LONG TERM...(Wednesday Through Sunday)
Issued at 345 AM MST Mon Feb 20 2017

Large scale trough will dig southeast across the Pacific NW
Wednesday, then move across the Rockies Wednesday night into
Thursday and across the plains through Friday. Latest medium range
model runs still not in very good agreement with regard to
evolution, timing, and track of upper level system and surface
features late this week. The 00Z EC and GFS have mostly swapped
tracks, with the GFS a bit further north and the EC further south.
EC is still stronger with the upper level portion of the system,
while both show the surface low still developing and tracking well
south of the area, across southeast CO and KS. Canadian is still
stronger than the other two and develops an upper low much
earlier, but its track is further south than previous runs. With
all this being said, the latest forecast is mostly based on
previous EC and 00Z GFS runs with a more northerly track, which
would result in the heavier snowfall potential still over southern
portions of the forecast area, generally south of Interstate 90
and especially across far southern SD. With this projected track,
there is potential for around 6 inches of snow over southern
portions of northeast WY and portions of southern SD. However, if
the trends of a further south track persist, then this potential
will shift south of most or all of the CWA, with lesser amounts
across the forecast area and little or no snow over northern
portions of the forecast area. Will continue to monitor latest
model runs and adjust the forecast as needed.

Main timeframe for snow would be Thursday into Thursday night, as
the system looks to be a bit slower to arrive. Colder air will
quickly move in, with some rain or mix possible southeast of the
Black Hills on Thursday, especially toward south central SD, before
changing to all snow. Lingering light snow is possible later
Thursday night into Friday depending on evolution of system as it
moves east of the region and also with any secondary energy behind
the system.

The weekend looks to be relatively cold, especially compared to the
last couple of weeks, with highs near or slightly below average.
Weak disturbances in west-northwest flow could bring snow showers to
some areas over the weekend, especially on Saturday.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Tuesday Morning)
Issued At 345 AM MST Mon Feb 20 2017

VFR conditions are generally expected through the forecast
period. Lingering light showers could produce local MVFR
conditions early this morning. West to northwest winds will be
breezy at times across the area today, especially across
northeastern WY and northwest SD.

&&

.HYDROLOGY...
Issued at 345 AM MST Mon Feb 20 2017

The warm weather of late has broken up the ice along the White
River. Some ice jams have developed along the 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, through the first half of
the week.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

SHORT TERM...26
LONG TERM...26
AVIATION...26
HYDROLOGY...26


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