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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
530 am CST Monday Nov 30 2015

Short term...(today through Tuesday afternoon)
issued at 323 am CST Monday Nov 30 2015

A slower start than what we had to the significant precipitation in
our eastern forecast area will still give way to a rapid increase as
the morning progresses. There will be patchy freezing drizzle Sioux
Falls south and east through early this morning...and snow will
probably be mixed with sleet during the morning in part of northwest
Iowa and a small part of southwest Minnesota near Jackson. Do not
anticipate freezing rain due to the shallowness and elevation of
the warm later and a resulting deep cold layer. Cooling should take
over by noon/18z. Otherwise precipitation with this storm will be
all snow.

The system still looks to have widespread effects...unlike the much
narrower event from ten days ago. The position and strength of the
low...short waves rotating around it...and the trowal/warm advection
pattern on the west side of the system are all factors. All of the
area should get heavy snow or close to it considering the lift
especially early will be deep enough for decent dendritic growth.
Have gone with a Winter Storm Warning for all but the far
southwestern three counties of our area. The warning will remain
through Tuesday evening in the original warning area and go through
Tuesday afternoon in the upgraded area west of the James River. The
above mentioned southwest corner will keep its advisory through
Tuesday afternoon. The expected snow amounts here are barely below
most of the area but the accumulations will be more spread out in
time. Still...we will have to watch this area for significant snow
lingering longer than expected...though by Tuesday afternoon snow
intensity should almost certainly be on the decrease from the west.
The basis for upgrading the warning for part of the west is the
increase in expected snow total there. Stronger winds than further
east are a small factor as they should not be strong enough to
produce significant blowing...but could result in a few more
drifting problems.

One part of the warning area that has the potential to get a bit
less snow is the far southeast including the Sioux City area as snow
accumulations could drop off sooner and become concentrated further
north. But this area also has the potential to get hit hard with
heavy snow today so it is best to keep the warning going there.

Temperatures are really not going to do too much changing through
Tuesday...with the most significant change being upstairs cooling
today as any sleet GOES over to snow. At the surface...around 30
highs today and Tuesday will compare with lows in the middle to upper
20s tonight.

Winds will begin to pick up gradually as they swing slowly around to
northerly and eventually northwesterly. All this will happen faster
over the southwestern part of our area with the proximity of the low
delaying the pickup in the east. As mentioned...winds as shown on
our blowing snow procedure do not seem strong enough to mention
blowing snow even west/southwest...but will reach what we would call
breezy levels.

Long term...(tuesday evening through sunday)
issued at 323 am CST Monday Nov 30 2015

Expect areas of light snow to linger into Tuesday evening as one
last lobe of energy rotates around the back side of departing upper
low. Possibly up to another half inch accumulation adding to the
total in our northeast...with lesser amounts to the west. Breezy
conditions persist into the night as well...bringing continued
potential for drifting...though this too should be diminishing as
the snow pack becomes more compacted. With these factors...current
expiration of warning at 06z Tuesday night looks reasonable and no
changes made there.

Beyond Tuesday night...broad upper ridging builds into the northern
plains...bringing much warmer air back into the region...above the
surface. Question is how much of this warming will be realized at
the surface with 7-10+ inches of new snow throughout much of the
region. 850mb temperatures by middle-late Friday vary from 5-10c...
depending on the model...with the Gem/GFS warmer than the European model (ecmwf).
Forecast would be expected...indicate very sharp
inversion beneath this warmer air...which does not seem unrealistic
given the snow cover. This also means that just a small difference
in depth of mixing could result in significant jump in surface
warming. Disparity seen most dramatically between the raw model
temperatures and numerical guidance though...with the former
generally keeping highs in the upper 20s to lower 30s...while the
latter warms most areas into the upper 30s to middle 40s. That said...
did not deviate much from general model blend at this point...which
holds highs in the 30s for most...with a few locations topping 40 in
our far west beneath warmest temperatures aloft.

With the shallow inversion and south-southwesterly low level jet
developing Friday night...would expect to see distinct elevation
signature in temperatures...thus bumped up lows a few degrees from blended
guidance in areas near/east of the Buffalo Ridge...and also in the
higher elevations of Gregory County.

Aside from temperature challenges...mid-longer range portion of the
forecast is pretty uneventful. Upper ridge should keep the region
dry through Friday...and even into next weekend appears moisture
slow to return ahead of northern stream trough dropping into the
northern plains expect little more than an increase in
clouds with this feature at this time.


Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 530 am CST Monday Nov 30 2015

Areas of VFR conditions through 15z north of Interstate 90 through
15z ahead of precipitation...otherwise widespread ceilings below
1k feet with visibilities 3-5sm and areas of visibilities below
3sm in snow. Areas -fzdz fsd south and east through 15z.


Fsd watches/warnings/advisories...
South Dakota...Winter Storm Warning until midnight CST Tuesday night for

Winter Storm Warning until 6 PM CST Tuesday for sdz052-053-

Winter Weather Advisory until 6 PM CST Tuesday for sdz050-057-

Minnesota...Winter Storm Warning until midnight CST Tuesday night for mnz071-

Iowa...Winter Storm Warning until midnight CST Tuesday night for

NE...Winter Storm Warning until midnight CST Tuesday night for nez013-



Short term...
long term...jh

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