Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 120313

Area Forecast Discussion
National Weather Service Sioux Falls SD
913 PM CST Wed Jan 11 2017

Issued at 910 PM CST Wed Jan 11 2017

Radically lowered pops along and north of I 90 and went just
flurries for those areas. This is because the NAM continues to
show a very dry layer from 900-850mb. Indeed, the 00Z ABR raob
shows a lot of dry air in the lower levels as the air gets
increasingly drier heading northward. Conversely, raised pops into
the categorical range of 80 to 100 percent in our far southern
zones. Snow amounts from Yankton to Storm Lake and points
southward will generally range from about a third of an inch to
just less than an inch of fluff. Low level saturation is not an
issue in our far southern zones, but the snowfall will not last
very long and thus will keep amounts down. Along I 90, it is
doubtful any snowfall will measure, perhaps some trace amounts
here and there.


.SHORT TERM...(This evening through Thursday)
Issued at 350 PM CST Wed Jan 11 2017

The main challenge tonight will be a shot for some light snow. A
strong upper level jet will be in place across the central Rockies
through Nebraska into southern Iowa. This energy will slowly drift
southward. A weak piece of energy will move through the area and
interact wit the fairly deep boundary that is supportive of all
snow. The better chances will transition from south central SD early
this evening towards Interstate 90 and northwest Iowa later this
evening and overnight. The chances will quickly drop off late
tonight but with some dendritic temperatures in the lower 1 to 2 km
some very light snow could linger into Thursday morning.

Northwest winds will increase a bit on Thursday which could cause a
little blowing snow across parts of southwest Minnesota. Not
expecting widespread problems as winds will be about 15 to 30 mph.
Wind chill values will fall to 15 below to 20 below zero north of
Interstate 90 late tonight into Thursday morning.

.LONG TERM...(Thursday night through Wednesday)
Issued at 350 PM CST Wed Jan 11 2017...CORRECTED

High pressure will be exiting east across the CWA during the evening
giving way to much colder conditions Thursday night into Friday
morning. Overnight temperatures are expected to drop from the single
digits above to the double digits below. While the winds will remain
on the light side, wind chills values will likely fall into the
double digits below zero. Therefore an advisory will be necessary by
tomorrow, mainly for areas north of the I-90 where wind chills are
expected to drop from -15 to -25F. After coordination with other
offices, will wait to issue due to ongoing headlines.

The week will be ending with more light precipitation across the
area as a weak shortwave slides into the area Friday morning into
Friday afternoon. Certainly there is some 700 mb frontogenetic
forcingwith this wave, but appears to be weakening in the 12Z
solutions. As the high pressure shifts east of the area, southerly
winds will be advecting warm air; thus enhancing the forcing.
Nevertheless, the potential for heavy precipitation is low due to
a lack in moisture. In terms of snow accumulation, just a couple
of tenths or so will be possible.

After the departure of the weak wave, quiet and more pleasant
weather conditions will prevail during the weekend. A warming trend
is still on track as a upper level ridge build into the area through
Sunday evening. High temperatures will be in the 20s to low 30s
under partly sunny skies.

The beginning of the work week promises to be very complex with snow
and mixed precipitation Sunday night into Tuesday morning.

A large low pressure system, currently located along the West coast
will be moving into the Midwest by Sunday; increasing the risk for
precipitation across the area. Model solutions diverge in terms of
track, timing and evolution of this system. The Canadian is a bit
quicker bringing the system across the central plains by Sunday
night/Monday morning, while the GFS and ECMWF lifts the low Monday
afternoon. Another concern with this system is the precipitation
type. Looks like snow will be possible for most areas, but thermal
profiles suggest mixed precipitation or a freezing rain event will
be possible across northwest Iowa. Due to the inconsistency of the
models and given the fact that this system is expected a few days
out, the confidence in the forecast details is moderate, but have
included the potential for mixed precipitation in the grids.

Behind this event, milder temperatures are anticipated for the rest
of the week. Temperatures will be above normal with highs in the low
30s by Tuesday and in the low to upper 30s by Wednesday.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 538 PM CST Wed Jan 11 2017

KHON will likely remain VFR through the TAF period. However a
quick moving weak disturbance will spread light snowfall tonight
for areas generally along and south of Interstate 90. Therefore
MVFR to IFR conditions are expected right during the overnight
hours at KFSD and KSUX. In fact KSUX could see some brief LIFR
around 06Z to 08Z Thursday as three quarters of a mile has been
reported under the snowfall at KVTN. Thursday will exhibit VFR
conditions as a cold front moves through the area bringing the
winds around to the northwest again.




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