Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
522 PM CST Tuesday Feb 9 2016
Short term...(this evening through wednesday)
issued at 240 PM CST Tuesday Feb 9 2016
Main concern in the short term will be the increasing chance of
light snow late tonight through the day Wednesday. Low level
baroclinic zone extending north to south across central South Dakota
will begin advancing slightly eastward late tonight...nearing the
James River Valley by middle morning on Wednesday. Meanwhile a middle
level wave drops south southeast from Canada...moving through the
forecast area during the day Wednesday. With broad but weak lift and
a modest forcing...a band of light snow noses into central South Dakota late
tonight then spreads southeast through the region during the day.
Expect some light snow late tonight in our far west...then spreads
into the i29 corridor around daybreak through middle-morning and across
our eastern half late morning. The light snow exits west to east in
the afternoon. South central South Dakota...west of the James where
saturation in the dendritic layer will be problematic...may not see
much in the way of precipitation. Elsewhere...accumulations will
range from around half inch to 2 inches of fluffy snow. With
temperatures in the single digits and teens across our central and
eastern counties where the greatest snow chances lie...expect some
fairly high ratios on the order of 15:1 to 20:1. Along the western
fringes of the precipitation snow will be much less efficient.
With the thermal boundary across the area...both low and high
temperatures will vary greatly. Expect lows to plummet to a few
degrees either side of zero in our extreme east...while warm air
advection moving into our western border and increasing middle clouds
will hold lows in the lower 20s in our west. May even see some non
diurnal readings late tonight in this area. Similarly....highs on
Wednesday will range from the lower teens near the Buffalo Ridge and
Iowa Great Lakes...to the middle 30s in Gregory County.
Long term...(wednesday night through tuesday)
issued at 240 PM CST Tuesday Feb 9 2016
After light snow exits quickly southeast Wednesday night...Thursday
looks to be chilly...but quiet for most areas. Our next chance for
light snow will fall quickly on the heels of wednesdays
system...with another minor shortwave tracking through the brisk
northwesterly flow aloft. Middle-level lift...slightly higher than
wednesdays system...will begin to overspread the region late on
Thursday...with an increase in upper support provided by left exit
region of an intensifying jet streak crossing The Rockies. While
model quantitative precipitation forecast remains on the light side...models have focused in on the
potential for prolonged light quantitative precipitation forecast over The Heart of the County Warning Area into
Friday morning. Snow amounts should generally remain under an inch.
Cold high pressure will enter the region on Friday...lingering into
the upcoming weekend. European model (ecmwf)/GFS differ a bit on the arrival of the
coldest air on Friday...but prefer the slightly more aggressive GFS.
That said...area setting up for a very cold start to Saturday
morning....especially in the eastern zones. With middle-level warm
advection quickly developing Friday night and a likely increase in
cirrus in the northwest flow...some concerns that western zones may be too
cold. If forecast does materialize...advisory criteria wind chills
may be felt over parts of Minnesota/IA/SD counties into Saturday morning.
Our next chance of snow will arrive Saturday into Sunday as a fairly
strong wave exits the Pacific northwest and enters the plains
Saturday night. GFS much stronger than the European model (ecmwf)...and therefore
lifts warm advection snow band quickly through and northeast of the
County Warning Area. With a weaker European model (ecmwf) solution preferred...feel that this snow
may stall closer to the County Warning Area...and especially the northeastern half of
the County Warning Area. This system would have the highest risk of a few inches of
snow...but the track is very uncertain at this time.
Behind this weekend system...trends continue to support a warmup
into next week.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 520 PM CST Tuesday Feb 9 2016
VFR conditions through most of tonight with winds becoming light
and variable. Light snow will develop in the north toward 10z then
overspread the area through Wednesday morning...resulting in
lowering ceilings and reduced visibilities.