Area Forecast Discussion
Issued by NWS Rapid City, SD

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532
FXUS63 KUNR 210247
AFDUNR

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

.UPDATE...
Issued at 736 PM MST Mon Feb 20 2017

Surface trof moving across eastern Montana/Wyoming this evening.
Gusty southwest winds developing across across northeast wyoming
and northern foothills. Latest HRRR/RAP along with 00z NAM show
winds continuing through the night. If trends continue, may
eventually issue high wind warning for southern portions of
northeast Wyoming. Potential for locally strong downslope winds
late tonight for northern/eastern slope of Black Hills. Have
adjusted winds up for northeast Wyoming into the Black Hills.
With the stronger winds, also raised low temperatures overnight.

The warm temperatures, low humidity, and gusty winds will put the
grassland fire danger index in the very high to extreme category
for much of western South Dakota on Tuesday afternoon.

&&

.SHORT TERM...(This Evening Through Tuesday Night)
Issued at 225 PM MST Mon Feb 20 2017

Upper trough across the central CONUS has shifted east of the CWA
with upper ridging building back in. Surface ridge has also built
into the region today with sunny skies. Quiet weather is expected
tonight through Tuesday. Warm air advection will return overnight as
southwest low level flow returns. Lows tonight will be in the mid
30s to mid 40s. Overnight temps in downsloping locations may end up
rising into the 50s as low level winds increase. Sunny to partly
cloudy skies are expected Tuesday along with another round of warm
air. Highs are expected to reach the 60s across northeast WY and
northwest SD...and low to mid 70s south and east of the Black Hills
into south central SD. An upper trough will push into the western
CONUS Tuesday into Tuesday night. Upper flow will become more
southwesterly Tuesday night with a series of waves cross the area.
This will bring some rain shower activity to the area during the
overnight hours.

.LONG TERM...(Wednesday Through Monday)
Issued at 225 PM MST Mon Feb 20 2017

Upper trough over the western CONUS will slide eastward over the
Rockies Wednesday into the central plains Thursday. The storm
system will strengthen across the plains and become stacked as it
slides northeastward Thursday and Friday from the plains to the
upper Midwest. Models are still trying to figure out the details
with this system, but the 12z runs continue the trend of a more
southerly track which takes the surface low across KS and the
majority of snowfall over the NE panhandle. The ECMWF/NAM/GFS all
agree on this southerly track while the GEM is the more northern
outlier which brings the heavier snowfall to southwest SD. Have
lowered pops/QPF slightly to reflect this more southerly track.
The snowfall looks to start late Wednesday night into Thursday
morning and continue until Thursday night or Friday. Highest
forecast snowfall amounts will be across the southern CWA
border...but still unsure as to snow accumulations. Cooler air
behind the departing storm will keep temps much lower than they
have been recently...near or slightly below average. Lingering
show will be possible through the end of the week into the
weekend.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 745 PM MST Mon Feb 20 2017

VFR conditions expected through Tuesday afternoon. Strong
southwest winds will continue through tonight across portions of
northeast Wyoming, with locally gusty winds across the Black
Hills. Low level wind shear expected on the plains of western
South Dakota late tonight/early Tuesday morning. The gusty west to
southwest winds will spread across the South Dakota plains
Tuesday morning.

&&

.HYDROLOGY...
Issued at 225 PM 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.
&&

$$

Update...7
SHORT TERM...13
LONG TERM...13
AVIATION...7
HYDROLOGY...Johnson



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