Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 121121

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
421 AM MST Thu Dec 12 2019

.DISCUSSION...(Today Through Wednesday)
Issued at 129 AM MST Thu Dec 12 2019

Upper level analysis shows weak ridging over the western CONUS,
and a weak trough sliding through the central states. A shortwave
moving through the western Dakotas is visible on water vapor
imagery. Radar and obs indicate some light snow over northwestern
SD. At the surface, stationary boundary is draped across the CWA.
Winds are light and variable, and temperatures are falling into
the teens and 20s.

A series of weak shortwaves will slide through northwest flow over
the next week or so, resulting in occasional light rain/snow and
varying temperatures.

Today, warmer air will advect into the area as the frontal boundary
shifts northeastward, allowing temperatures most places to rise into
the 30s and 40s. Some light snow will be possible across
northeastern WY and northwestern SD tonight with the next shortwave.
Lows will be around 20.

Right behind tonight`s wave will be another on Friday,
accompanied by a cold front and more light precipitation. Breezy
northwesterly winds will contribute to upslope enhancement over
the northern Hills, but limited moisture will result in only an
inch or two of snow there, and less on the plains. Highs Friday
are expected to be around average - in the 30s - before colder air
sinks into the region for the weekend.

A cold Canadian surface high will push into the northern plains
Friday night into Saturday. As temps dip into the single digits
and teens, light upslope winds may result in some freezing fog
around the Black Hills Saturday morning. Upper energy to the south
will bring chances for light snow to southern portions of the CWA
Saturday and Sunday, with minimal accumulations. Highs Saturday
will range from around 10 across north central SD to the lower 30s
farther south and west.

The northern plains will remain beneath the cold airmass into early
next week. Midweek, models are in agreement on western CONUS
ridging and some warmer air moving back into the region.


.AVIATION...(For the 12Z TAFS Through 12Z Friday Morning)
Issued At 416 AM MST Thu Dec 12 2019

Areas of IFR CIGS and patchy -FZFG will be located over
northwestern South Dakota until around 18Z. VFR conditions will
then prevail through the afternoon. Areas of MVFR/LCL IFR
conditions will develop toward central South Dakota around 01Z
this evening and will dissipate around 10Z early Friday morning.
There is a slight chance of rain or snow over parts of
northeastern Wyoming and northwestern South Dakota this evening.




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