Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
101 PM CST Friday Dec 26 2014
Short term...(today and tonight)
issued at 248 am CST Friday Dec 26 2014
Weak upper level wave and saturated to near saturated dendritic
temperatures supporting continued light snow over central parts of
South Dakota. Will go ahead and cancel the Winter Weather Advisory
for central South Dakota however as the snowfall is very light and
wind is not a major factor. This marginally saturated environment
dries up a bit shortly after sunrise with what looks to be a bit
of a lull in most locations middle morning into middle afternoon. By middle
to late afternoon a fairly strong upper level wave will ride
northeast and allow middle level winds to back...bringing increased
middle level convergence to the southeast half of the County Warning Area.
Instability above the front not impressive but there is a little
so a band of snow is expected...but at this time not expecting a
tight band with heavy amounts. That being said...the general
consensus is for about a quarter to a third of an inch of liquid
which will easily support 3 to 4 inches of snow. With the
increased confidence went ahead and issued a Winter Weather
Advisory for parts of far southeast South Dakota...northwest Iowa and
southwest Minnesota. North to northwest winds will not be
excessively strong but do anticipate some gusts to around 25 miles per hour
at times this afternoon and evening. Temperatures will not change
much from where they are now...and in some locations may fall a
bit through the day. Highs will mainly be in the 20s. Some of the
strongest forcing swings through from about 0z Saturday through 9z
Saturday and expect some of the better accumulations to occur
then. Some clearing will be likely as the wave exits late
tonight...so went with single digit lows in central South Dakota. Farther
east the clouds will hang strong so teens to lower 20s should be
more common by Saturday morning.
Long term...(saturday through thursday)
issued at 248 am CST Friday Dec 26 2014
Lingering snow will no doubt be rapidly moving east of the area
early Saturday morning and will carry a chance of light snow
for the early morning only...no chance in this flow of the system
even slowing down. Skies are expected to clear very well Saturday
with subsidence/drying preventing significant lingering low clouds.
Winds will be quite modest and with a surface ridge quickly moving
over the area...the day will be quite nice outdoors despite
highs in the lower 20s.
Sunday through Monday will bring the slow approach and passage of
a cold front associated with a Canadian wave driving colder air
which will be in for a few days next week. Middle and some low level
moisture will result in some chance of light snow Sunday night and
Monday. At this time expect very little because the 00z NAM...which
moves the Canadian wave slower southeast and allows for a modest
westerly wave bringing more snow to the area...seems to be a loner
on that. Once the front passes we will have a couple days of below
zero nights and cold days with no real precipitation threat...before
temperatures moderate late next week on a developing Canadian
northwesterly upper flow...still with no precipitation threat.
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1259 PM CST Friday Dec 26 2014
MVFR conditions to continue through most of the day until -sn
begins to fall as main dymanics approach the forecast area late
this afternoon into the evening. Kfsd and ksux will mainly be
affected by the storm in the form of reduced visibilities. Ceilings
and visibilities should begin to improve after 14z...but earlier then
that at khon.
South Dakota...Winter Weather Advisory from 6 PM this evening to 6 am CST
Saturday for sdz062-066-067.
Winter Weather Advisory until 3 am CST Saturday for sdz068>071.
Minnesota...Winter Weather Advisory from 6 PM this evening to 6 am CST
Saturday for mnz080-081-089-090-097-098.
Iowa...Winter Weather Advisory from 6 PM this evening to 6 am CST
Saturday for iaz001>003-012>014-021.
Winter Weather Advisory until 3 am CST Saturday for iaz020-031.
NE...Winter Weather Advisory until 3 am CST Saturday for nez013-014.