Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
337 am MST Thursday Dec 25 2014

Short term...today through Friday night
issued at 328 am MST Thursday Dec 25 2014

Water vapor imagery shows a deep trough strengthening across the
western Continental U.S. With the axis/developing cutoff low now crossing the
Great Basin. Surface analysis Show Low pressure strengthening across
the central to northern High Plains. Kudx radar shows snow has developed
mainly north of Interstate 90 and it gradually expanding in
coverage.

Upper trough will continue to develop today into a cut off low over
the Great Basin with strong forcing over Wyoming into western SD/neb. Band of
snow will slide south through the day...at a faster pace than models
had been showing previously. Now it appears snow will clear northwest South Dakota
quite early this morning if not already...and be more focused on the
Black Hills to scntrl South Dakota by the afternoon hours. Snow will then continue to
work through the southern County Warning Area this evening and taper off over scntrl late
tonight. Snow amounts still appear to be in line with 3 to 6 inches
of accumulation...with a few areas possible getting slightly higher
amounts. One of those areas may be the northern Black Hills. A cold
front will cross the area today with northwest winds 15-20kt behind the
front. As a result...upslope conditions will develop over the Northern
Hills. However...upsloping will be relatively weak...but it may be
enough to produce an additional inch or two over the Northern Hills.
There will be some blowing snow...but it isnt expected to be
significant.

The upper low will push across The Four Corners Friday with the best
lift staying S/southeast of the County Warning Area. Surface high pressure will build over
the northern plains with colder temperatures over the region. Highs will reach
the upper teens to middle 20s...with some mix of sun and clouds
expected.

Long term...Saturday through Wednesday
issued at 328 am MST Thursday Dec 25 2014

Persistent northwest flow will be found across the area for
extended period as ridge builds across the northeast Pacific into
Alaska. This will favor intrusions of Arctic air into the northern
plains...with below average temperatures. Saturday will feature
increasing clouds with weak middle level warm air advection. Shortwave digs into the
northern rockies/Great Basin Sunday into Monday. Broad area of
isentropic lift sets up across the area late Sunday into Sunday
night. Meanwhile...Arctic air spills through southern
Canada...reaching western South Dakota Sunday night. Blustery and
much colder on Monday. A few inches of snow possible Sunday
night/Monday. 1050+ mb Arctic high settles in over area for
Tuesday...with highs 20-30f below average. Some moderation in
temperatures for Wednesday/Thursday.

&&

Aviation...for the 12z tafs through 12z Friday morning
issued at 328 am MST Thursday Dec 25 2014

Widespread IFR ceilings/visibilities expected for much of the day with
snowfall...especially along and south of Interstate 90. The snow
will end from north to south late this afternoon/evening.
However...MVFR/IFR ceilings will persist through tonight.

&&

Unr watches/warnings/advisories...
South Dakota...Winter Weather Advisory until 11 PM MST this evening for sdz012-
013-024>032-041-072>074.

Winter Weather Advisory from 11 am MST /noon CST/ this morning
to 5 am MST /6 am CST/ Friday for sdz042>044-046-047-049.

Wyoming...Winter Weather Advisory until 11 PM MST this evening for
wyz054>058-071.

&&

$$

Short term...13
long term...7
aviation...7

National Weather Service Glossary of Abbreviations