Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
631 PM CST Monday Nov 24 2014
Short term...(this evening through tuesday)
issued at 348 PM CST Monday Nov 24 2014
Tonight 850 mb warm advection ahead of surface low will result in cooler
overnight lows tonight even though 850 mb temperatures were colder Sun night.
Cloud cover and strong wind on Sun night/Monday morning kept temperatures
from getting too cold but that wont be the case tonight. Skies are
clearing quickly from west to east this afternoon and will remain
mostly clear through a good portion of the night. Wind will also
begin to decrease just after sunset...decreasing to around 10 miles per hour or
less by midnight.
Soundings show some indication of moisture return in the pre dawn
hours with a stratus layer forming west of the James then moving
east. Temperatures in the west may hold steady or rise a degree or two
after clouds roll back in.
Tuesday will be cloudy and not nearly as windy as today. Temperatures will
actually climb at or just above freezing during the day.
Long term...(tuesday night through monday)
issued at 348 PM CST Monday Nov 24 2014
Models starting to come into much better agreement in the track and
timing of the clipper wave on Tuesday night and Wednesday. Models
continue to trend the wave further southwest...bringing the brunt of
the forcing across the northeastern half of the forecast area. A
band of light to moderate snow will spread southeastward across the
region Tuesday evening and quickly exit by daybreak on Wednesday.
The best forcing track east of a line from Huron to Sioux Falls to
Cherokee...where the greatest snowfall is expected. Amounts west of
here will be pretty light at around a half inch or less while along
and to the east should see a quick 1 to 3 inches. The wave will be
very fast moving with northwest winds increasing behind it around 15
to 25 miles per hour with higher gusts. The stronger winds arrive after the
snow ends...but may cause some blowing snow concerns into the day on
Wednesday. Temperatures will maximum out in the 20s early Wednesday and
fall some later in the day.
Stratus continues to blanket the area through Wednesday night...but
temperatures will still drop into the single digits to middle teens for
lows with the cold airmass settling into the northern plains. On
Thursday...however some thinning may work into our northeast where
the influence of high pressure may squeak in. Highs will also be
coolest in the northeast in the upper teens...however some light
return flow developing Thursday afternoon west of the James River
will boost readings closer to 30.
Still looking at some continued model divergence Thursday night and
Onward with regards to the location of the baroclinic zone draped
over the northern plains. Looks like the general consensus is to
lift it northward into Friday...allowing some decent warm air
advection to spread across the forecast area. Middle level temperatures
are pretty mild on Friday and Saturday...but model/ensemble spread
of temperatures is high. While our southwest will likely see decent
warming...snowcover from the clipper system may slow warming a bit
across our northeastern half. Still...looks like a good shot for
highs back above freezing across the County Warning Area both days. Near the
Missouri River highs may even top out in the middle 40s to lower 50s on
The west northwest upper flow turns more westerly or southwesterly
next week. Not a great deal of confidence in temperatures or where
the thermal boundary will set up...so did not alter the allblend
numbers any. Precipitation chances appear to be very low during the
period as well...but would not be surprised if this changes in
future runs. Will leave conditions dry for now.
Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 629 PM CST Monday Nov 24 2014
Mainly VFR through sunrise tomorrow morning...although some MVFR
to near IFR ceilings will be possible in central South Dakota late tonight.
An upper level low pressure will move into the area on Tuesday
which will bring the threat for snow late in the period. The best
chances for snow will be shortly after the end of this taf period.