Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
532 am CST Monday Nov 24 2014
Short term...(today and tonight)
issued at 330 am CST Monday Nov 24 2014
Windy and chilly on this current overnight as deep low continues to
evolve across the Great Lakes. Main impact across the local area
will be wind. Profiles indicate that while wind gusts to 45 miles per hour are
not probable...will likely get periods of sustained winds around 30
miles per hour through the day...especially latter morning and early afternoon
as weak lobe of upper low wraps by to the east. No indication of
changes needed to lower end Wind Advisory across eastern County Warning Area...and
expect a gradual drop in winds by very late afternoon...ending time
seems reasonable by around sunset...if not a bit before.
Have started to see some very light precipitation occur across
eastern South Dakota into western Minnesota overnight. Some reports
of freezing drizzle north of the County Warning Area...but thus far have not had any
reports of any freezing drizzle in SW Minnesota and north facing webcams
have not shown any tendency for icing. With forecast radiosonde observations showing
window closing rapidly for any freezing drizzle as temperatures cool to ice
favoring in the cloud layer...will only keep a patchy mention in the
far eastern areas for a couple more hours. Cooler surge centered on
I 29 has brought a few flurries with the light returns on radar.
Overall...system will be far from a prolific precipitation producer
across the fsd County Warning Area...and in fact am fairly confident that measurable
precipitation is quite unlikely. Deep forcing for lift is fully lacking...
and most of the more usable moisture is locked to lower levels. Will
have the near surface layer fairly unstable which should help to
produce periods of flurries through much of the day... mainly east
of the James Valley. Have held on to some very low measurable probability of precipitation
only across parts of SW Minnesota...as will be closest to slightly deeper
moisture with lobe wrapping around upper low. Temperatures today very
limited recovery...but loss of much of the snow cover will allow US
to squeeze out about every potential degree we can...near 20 north
to the upper 20s Missouri Valley.
Winds diminish and skies gradually work on clearing this evening
with weak ridging at the surface and aloft slipping eastward. Late
tonight...shallow warm air advective layer begins to return and push
into the western third of the County Warning Area. Indications of a little moisture
gathering in shallow thermal gradient. There is a subtle middle level
wave which translates rapidly to the southeast over this boundary
late night...and perhaps will be enough to prompt some ice
formation. Otherwise...an outside concern that shallow nature to
moisture /less than 4500 feet above ground level/ would bring a chance for some light
freezing drizzle as far east as the middle James Valley by daybreak
Tuesday. With shear somewhat less than would like to see...and pre-
existing drier layer in advance...have not mentioned any freezing
drizzle...but did throw in some patchy fog and a few flurries at
present. Temperatures will likely head toward non-diurnal through the
western areas with increase in clouds and winds turning toward more
Long term...(tuesday through sunday)
issued at 330 am CST Monday Nov 24 2014
Any flurries and fog west would linger early Tuesday morning then
should dissipate. Clipper with seemingly decent upper support but
marginal moisture will approach the area and bring a light snow
potential Tuesday afternoon and night...especially northeast.
Questionable coverage due to the marginal moisture leads to keeping
maximum probability of precipitation at a high chance level...and amounts should stay less than
an inch. Despite the apparent decent dynamic support...
frontogenetical forcing does not seem too great. Will continue to
mention some rain mix in the southwest with the low probability of precipitation...though
any more than minimal precipitation during the day would go to all
snow. Temperatures will warm into the 30s with the warmer
highs near 40 in the southwest.
Cooling will come in behind this system...making itself most
apparent in little temperature warming Wednesday from morning lows.
A little light snow could linger early far east.
Otherwise...clearing should be just partial Wednesday as a warm
advection pattern sets up over the Western Plains. Some light snow
or flurries could still develop southwest Wednesday night but with
little upper support and continued marginal moisture it would not be
Thanksgiving day should be dry and modestly cold with varying cloud
cover as back door surface high suppresses warm advection pattern.
Models are going for a quick warmup Friday then a cooldown again for
the weekend. Have gone with the extended guidance and kept
precipitation mention out for Friday through Sunday...though it
seems a little light snow with the arrival of the colder air
Saturday would not be out of the question. The strength of the
warmup Friday is in question. Extended guidance keeps it modest.
Given the rapid nature of the warmup and the potential lag at the
surface have gone with the guidance...but if we still have lack of
snow cover it could get balmier.
Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 532 am CST Monday Nov 24 2014
Widespread MVFR ceilings expected today...gradually eroding from
the north and west during the afternoon. Surface winds gusts from
the northwest will gust to 30 to 35 knots for much of the day...
lingering east of Interstate 29 into the evening hours. Occasional
flurries are expected...especially from middle morning to the early
afternoon hours as lobe of upper level system brushes by through
Minnesota. Likely that any reduction of visibility into MVFR range
would be brief.
South Dakota...Wind Advisory until 6 PM CST this evening for sdz040-056.
Minnesota...Wind Advisory until 6 PM CST this evening for mnz071-072-080-081-
Iowa...Wind Advisory until 6 PM CST this evening for iaz001>003-013-014-