Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 151704

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1104 AM MDT Thu Mar 15 2018

Issued at 745 AM MDT Thu Mar 15 2018

Issued a dense fog adv for the foothills area given saturated
upslope flow under a staunch inversion. Fog should begin to lift
late this morning as diurnal heating warms the BL.


.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 18Z TAFS Through 18Z Friday)
Issued At 1058 AM MDT Thu Mar 15 2018

IFR/LIFR conditions in fog will continue to improve early this
afternoon. Low ceilings will linger through the day across
northwest South Dakota, with VFR ceilings elsewhere. Precipitation
will develop this evening across northeast Wyoming and western
South Dakota with rain/freezing rain changing to snow. IFR/local
LIFR conditions are expected in snow, which will be heavy at


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.

     Dense Fog Advisory until 11 AM MDT this morning for SDZ012-025-

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



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