Winter Storm in Wyoming, February 8 to 9, 2018

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
148 PM MST Thu Feb 8 2018

.DISCUSSION...(This Evening Through Thursday)
Issued at 148 PM MST Thu Feb 8 2018

Low-level baroclinic zone remains over western SD and northeast WY
this afternoon under northwest flow aloft. High pressure over
western Canada is beginning to nose southward into the northern
CONUS, leading to single digit temps above and below zero.
Southern extent of cold air is beginning to spill into the SD
Plains, with temps over much of western SD in the low teens to low
20s. Strong low-level inversion is evident over the Black Hills,
where temperatures at higher elevations have reached the upper
40s to even 50 at Mt. Rushmore. Farther west into northeast WY,
warm air extends to the surface, with widespread low-to-mid 40s
over the westernmost portions of our CWA.

Across southwestern SD, we're currently in a bit of a precip lull as
an upper-level jet streak over the Northern Plains partially
responsible for this morning's snowfall moves eastward over the
Midwest. Suspect precip coverage and intensity will increase again
as we continue through the late afternoon and evening owing to
approach of primary vort max and deformation zones aloft. Most
models are suggesting an enhanced band of precip (or potentially
multiple bands) will likely set up this evening into the overnight
hours as 850-500 mb fgen ramps up. Confidence is low in exact
location of this band, but it is likely to cause some locally
enhanced snowfall accumulations across northeast WY through the
central/southern Black Hills and onto the southwestern SD Plains.
With steep lapse rates above a residual midlevel inversion later
tonight, may also see some convective elements that could locally
enhance snowfall rates.

Precip type will be a concern through approximately 03-06z before
surging cold air wipes out inversion over the area. Do expect some
minor ice accumulations due to freezing drizzle/rain, especially
over the central and eastern Black Hills and adjacent Foot
Hills/Plains. Over higher elevations of the Black Hills and portions
of Campbell/Weston Counties in Wyoming, precip may remain liquid
through at least 00z before gradually transitioning to snow.

Current warnings and advisories generally remain on track. Have
added a winter weather advisory for southern Campbell and Weston
zones in Wyoming beginning 03z Friday to account for brief freezing
rain and subsequent transition to snow. Once snow ends across
northwestern zones tonight, we will reevaluate the need for a wind
chill advisory following the expiration of winter storm
warning/winter weather advisories. Though winds should generally
decrease after 06z, local wind chills could approach 25 below zero late
tonight into Friday morning.

Arctic high builds into the region Friday into Saturday, with
coldest temps generally expected Saturday morning. General warming
trend is expected through early next week. However, with continued
progressive, northwest flow aloft, will likely deal with a couple
quick-hitting, low-impact events through next week. Appears first
such system will affect the area Monday, with another approaching
midweek. For now, no big concerns with these disturbances, though
may have to watch for brief wind chill concerns Monday night into
Tuesday morning.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1024 AM MST Thu Feb 8 2018

IFR/LIFR conditions due to snow/local freezing rain/sleet will
continue through this evening over far northeast WY into
northwest/south central SD. Further southwest, mix of VFR/MVFR
conditions expected with patchy -RASN. Precipitation will
overspread entire area tonight and will change to all snow with
widespread IFR/LIFR conditions expected.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 11 AM MST /noon CST/ Friday for
     SDZ024>032-041>044-046-047-049-072>074.

     Winter Storm Warning until 11 PM MST this evening for SDZ001.

     Winter Weather Advisory until 11 PM MST this evening for SDZ002-
     013-014.

     Winter Weather Advisory until 5 AM MST Friday for SDZ012.

WY...Winter Weather Advisory until 11 AM MST Friday for WYZ057.

     Winter Weather Advisory from 8 PM this evening to 11 AM MST
     Friday for WYZ055-058.

     Winter Weather Advisory from 5 PM this afternoon to 11 AM MST
     Friday for WYZ054-056.

     Winter Weather Advisory until 5 AM MST Friday for WYZ071.

&&

DISCUSSION...Sherburn
AVIATION...Helgeson

Hazardous Weather Outlook
National Weather Service Rapid City SD
520 AM MST Thu Feb 8 2018

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-091300-
Harding-Perkins-Butte-Northern Meade Co Plains-Ziebach-
Northern Black Hills-Northern Foot Hills-Rapid City-
Southern Foot Hills-Central Black Hills-Southern Black Hills-
Custer Co Plains-Pennington Co Plains-Haakon-Fall River-
Oglala Lakota-Jackson-Bennett-Mellette-Todd-Tripp-
Sturgis/Piedmont Foot Hills-Southern Meade Co Plains-
Hermosa Foot Hills-Northern Campbell-Southern Campbell-
Western Crook-Wyoming Black Hills-Weston-Northeastern Crook-
520 AM MST Thu Feb 8 2018 /620 AM CST Thu Feb 8 2018/

This Hazardous Weather Outlook is for portions of western South
Dakota and northeastern Wyoming.

.DAY ONE...Today and Tonight

A winter storm will continue to affect the region into Friday.
Accumulating snow can be expected for most of the region, with the
highest amounts over northwest South Dakota and the Black Hills.
Some light freezing rain is also possible, mainly along and south
of Interstate 90. Winter storm watches and warnings are in
effect for portions of the area.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Snow will taper off Friday morning as a winter storm exits the
region. Wind chills of 15 below to 25 below can be expected
Friday morning.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today.

&&

Stay tuned to NOAA weather radio for further updates...or check
our web site at weather.gov/rapidcity

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RAPID CITY SD
247 PM MST THU FEB 08 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0246 PM     SNOW             9 WSW RED ELM           44.99N 101.96W
02/08/2018  E2.5 INCH        ZIEBACH            SD   TRAINED SPOTTER

            2-3 INCHES NEW SNOW SINCE THIS MORNING.

&&

WFO UNR