Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 191756

Area Forecast Discussion
National Weather Service Sioux Falls SD
1256 PM CDT Mon Mar 19 2018

.SHORT TERM...(Today and Tonight)
Issued at 355 AM CDT Mon Mar 19 2018

Near term issues center around abundant low level moisture, and
continued areas of fog and/or drizzle early this morning. Again
dealing with a deep, relatively dry northeast flow above this low
level moisture. Aside from some patchy drizzle, this will limit
extent to which precipitation will be able to advance into the
forecast area through the day. Thus have further trimmed pops for
today, confining to areas mainly west of the James Valley until late
in the day when upper wave drops into central South Dakota. This
will provide increased lift to eventually overcome dry layer and
allow some light precipitation to expand eastward. The moist low
level air mass should help keep surface temperatures above freezing
as the precipitation initially advances toward I-29 late in the
afternoon, limiting any potential for any minimal snow accumulation
prior to 00Z to just higher elevations in our far western counties.

Surface/boundary layer temperatures will cool below freezing this
evening as the wave slowly advances east, allowing rain to change
over to light snow through the night. Wave is rather slow-moving,
but not seeing any mid level front or deep lift that would focus a
heavier band, so still expecting just a broad light snowfall over
the area. Amounts generally 1-3 inches, with the highest amounts in
our higher elevations in southwest Minnesota/east central South
Dakota, where cooling will reach the surface more quickly.

.LONG TERM...(Tuesday through Sunday)
Issued at 355 AM CDT Mon Mar 19 2018

Light snow will be lingering near/east of I-29 by daybreak Tuesday,
generally exiting by midday, but a secondary weak wave will drop
southeast into the region Tuesday afternoon/night that will keep a
slight precipitation chance around into Tuesday night. GFS/Canadian
a bit more robust with this wave than NAM/ECMWF, and will keep pops
quite low as a result. However, will have to watch this wave for the
potential for another light dusting of snow Tuesday night for parts
of the area.

Temperatures will warm midweek as modest upper ridge builds into the
region, with highs in the 40s and 50s by Thursday. This in advance
of a lead wave bringing a good chance of precipitation to the region
late in the work week, followed by a more potent trough which could
impact the region next weekend. At this time, thermal profiles would
support either rain or snow, with minimal snow accumulations with
the first wave Friday as temperatures again warm into the 40s and

More uncertainty in strength/track and associated snow potential
with the weekend system. Current consensus would point to some
accumulation, primarily across northeast portions of the forecast
area, but ensembles show very broad range in not only precipitation
amounts, but also low-level temperatures which will be critical to
precipitation type. Will certainly be a system to monitor as we
progress through the week.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1256 PM CDT Mon Mar 19 2018

Drier trajectory in the lower levels on northeast flow has pushed
the MVFR and IFR ceilings back to the James River valley and
westward at midday, but gradual encroachment of upper trough with
development of light precipitation will again lower ceilings from
the west, as well as some potential for diurnal redevelopment of
scattered to broken MVFR cloud heights. Will see band of mainly
snowfall by evening spreading eastward overnight, and will likely
get period of IFR or briefly lower ceilings and visibilities as
this band of snowfall works through the TAF sites. Lingering
inverted trough through midday Tuesday will keep winds light, but
ceilings largely in the IFR range east of the James River.




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