Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 150853

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
253 AM MDT Thu Mar 15 2018

.DISCUSSION...(Today Through Wednesday)
Issued at 250 AM MDT Thu Mar 15 2018

The latest water vapor animation shows a big trough and upper low
over the western CONUS/eastern Pacific. This will be sending a
series of short-wave troughs across the CWA the next several
days, with the most substantial trough affecting the area tonight
and Friday.

The models agree well with notable upper-level divergence and
low- level warm advection/isentropic lift for much of the CWA
tonight and Friday, especially across the Black Hills and
southwestern SD. Thermal profiles and the SREF guidance point to
a good chance of freezing rain over parts of southwestern and
south-central SD, although a mix also is possible over other
parts of the CWA as well.

Have updated the watch to a winter storm warning where confidence is
greatest over the central/southern Black Hills and far southwestern
SD for six inches plus of snow. Elsewhere, enough uncertainty
exists on location of heaviest precipitation along with rain/snow
transitions. Nevertheless, have added northern Campbell County to
the watch as it appears there could be a little more snow there
than previously forecast. In addition, have added Tripp County to
the watch where substantial freezing rain is possible.

Given the moist-neutral vertical temperature profiles and some
potential for frontogenesis, would not be surprised to see a
narrow band of 6-12 inch snow amounts on Friday, but pinning down
the exact location is not possible at this time.

The snow should end Friday evening, but then another trough will
move across the area Sunday and Monday. This looks to be weaker
than the current system, also with the main rain/snow farther
southeast than for Friday`s storm. Another weak trough will pass
through the area Tuesday with some snow/rain showers, but after
that ridging and warmer weather should prevail for Wednesday and


.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 1108 PM MDT Wed Mar 14 2018

Fog/stratus will develop across portions of northwest South
Dakota overnight with IFR ceilings and visibility. the stratus/fog
expected to make it into the KRAP terminal. Low ceilings will
linger through the day across northwest South Dakota, with VFR
ceilings elsewhere. There is a small chance for some light
precipitation across northeast Wyoming and the Black Hills area
late tonight into Thursday morning, which could be in the form of
rain, freezing rain, and/or sleet. Precipitation will increase in
coverage Thursday evening across northeast Wyoming and western
South Dakota with rain/freezing rain changing to snow.


SD...Winter Storm Watch from late tonight through Friday afternoon
     for SDZ012-024>026-031-032-043-044-046-047-049-072-073.

     Winter Storm Warning from midnight tonight to 3 PM MDT Friday
     for SDZ027>030-041-042-074.

WY...Winter Storm Watch from late tonight through Friday afternoon
     for WYZ054-056>058-071.



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