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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
1111 PM CST Sat Dec 27 2014

Short term...(this evening through sunday)
issued at 400 PM CST Sat Dec 27 2014

For tonight a weak ridge of high pressure will move across eastern
South Dakota and into Minnesota and Iowa after midnight. Other
than a patch of stratus near Highway 14...skies will be clear to
start the night. With winds light and fresh snow
cover...temperatures should drop quick this evening. Then middle
clouds will begin to increase and least at higher
elevations...will begin to increase from the southwest. So kept
lows in the single digits above zero. If skies stay clear
longer...some valley locations could approach zero.

The significant feature for Sunday will be the southward moving
Canadian cold front. This front will move across Highway 14 around
sunrise...reach i90 late morning and move south of Highway 20 by
early afternoon. Not the typical mixy frontal passage expected as
winds go northeast behind the front. Rather expect cold air to ooze
in through the day. Also expect some stratus to overspread at least
north of i90 by late morning. For temperatures I think it will mean
a morning rise north of i90 with steady or a slow fall in
temperatures in the afternoon while temperatures south of i90 reach
maxes in the afternoon. Winds will not be too strong...generally 10
to 20 miles per hour. upper wave will be approaching the eastern plains
tomorrow afternoon. It will start out dry at low levels but where
lift is maximized above 700 mb...the atmosphere is very favorable
for dendritic snow growth. So expect virga to develop in the early
afternoon in south central South Dakota with flurries or even light
snow by late afternoon. Any accumulation prior to 00z Monday should
be minimal.

Long term...(sunday night through saturday)
issued at 400 PM CST Sat Dec 27 2014

Models in pretty good agreement regarding the next system to
bring wintry weather to the region. Thermal boundary sets up near
the Missouri Valley on Sunday evening ahead of an upper level
shortwave dropping into the northern High Plains. The wave will
gradually sag across the Black Hills into north central Nebraska
Sunday night...before finally shifting well south of the region
Monday morning. Modest middle level frontogenesis moves along the
Missouri Valley along with a broad area of divq tracking to the
southeast. Snow production will be efficient...with model sounding
suggesting a thick dendritic growth layer. Snow ratios could very
well be 20:1 or even higher. Best chance for snow will be south of
i90...closest to the Missouri River where preliminary amounts of an
inch and a half to 3 inches of very light fluffy snow is expected.
Amounts taper off to a half inch or less north of a Wessington
Springs to Sioux Falls to Spencer Iowa line. Given nearly Universal
model agreement that the MO valley will see some measurable
snow...have bumped up probability of precipitation to the likely category.

Cold Arctic high pressure settles into the region behind the
shortwave Monday afternoon into Tuesday. Skies will become mostly
clear from north to south Monday night. Lows will plummet into
the single digits and low teens below zero. Highs on Tuesday will
be quite cold in the single digits above zero.

A warming trend arrives on Wednesday and Thursday with split flow
keeping the region dry. The northern stream drops southward Thursday
night while an upper level cut off over the Desert Southwest begins
advancing towards the plains. Looking at some significant timing
difference in the evolution of this confidence is very
low in the later half of next week. Left in the low chance snow probability of precipitation
for Friday from the allblend for now. Highs will return to the 20s
Thursday and Friday.


Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1110 PM CST Sat Dec 27 2014

VFR conditions will prevail until southward progression of
Arctic frontal boundary late tonight and Sunday...behind which
will spread MVFR stratus. temperatures in the cloud layer
cool...may also find some potential for brief MVFR visibility in
flurries for khon and kfsd. Light snowfall chances limited to ksux
after 03z where stronger frontal forcing and less imposing dry
layer between middle clouds and lower clouds before onset of stronger


Fsd watches/warnings/advisories...
South Dakota...none.


Short term...schumacher
long term...

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