Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 220351

Area Forecast Discussion
National Weather Service Sioux Falls SD
1051 PM CDT Wed Mar 21 2018

Issued at 828 PM CDT Wed Mar 21 2018

After looking through the 18Z model data, along with ensemble
data, have slightly modified surface temperatures downward
slightly Friday and Friday evening given greater potential for
evaporative cooling. This results in a faster turn over to snow
in elevated areas of the Buffalo Ridge Friday. For surface
temperatures have leaned a bit heavier on the 50 percentile
numbers from model blends, which take 1-3 degrees off the surface
temperatures from previous forecast in the Ridge areas.

The end result bumps up snow totals an inch or two, and given the
potential of the snow event visible in plume data, feel issuing a
watch is warranted for a few counties in the northeastern CWA.


.SHORT TERM...(This evening through Thursday)
Issued at 415 PM CDT Wed Mar 21 2018

Scattered low clouds across east central SD into southwest Minnesota
and northwest Iowa will continue to shift eastward late this
afternoon and evening. Some mid level moisture increases near the
Missouri Valley late this evening and overnight, bringing some
additional mid and high clouds late. Winds will remain relatively
light from the east. Some patchy shallow fog will be possible mainly
in low lying areas such as rivers and streams, but do not expect
widespread fog development. Lows tonight will fall into the upper
20s to lower 30s.

Upper level ridge axis over the highs Plains continues to shift
eastward ahead of the next system to impact the region late week.
Skies will be mostly sunny to partly cloudy with mild temperatures
expected. With east winds around 7 to 12 mph, mixing will be less
favorable, but early spring sunshine will manage to warm
temperatures in the 40s and 50s. The highway 20 corridor may even
reach near 60.

.LONG TERM...(Thursday night through Wednesday)
Issued at 415 PM CDT Wed Mar 21 2018

The active weather pattern expected late this week into early next
week, as several systems impact the central and northern Plains.

Trough digs into the southwest US Thursday night and Friday, while
surface low pressure strengthens in eastern Colorado. East-southeast
winds increase Thursday night into Friday with light rain developing
in central SD late Thursday night. Initially, drier air will slow
the spread of rain into I-29 and points eastward, however by late
Friday morning, rain will become more widespread. The surface low
tracks east near the Kansas and Nebraska border Friday and Friday
evening while strong mid level frontogenesis and upper forcing
setting up over the heart of the forecast area.

With clouds and ongoing precipitation across the area, went ahead
and cooled hourly temperatures and highs on Friday into Saturday
morning using 50 percent superblend and 25 percent each of GFS and
ECMWF. Temperatures will be a key component in the eventual
precipitation type, with readings near or not much above freezing,
and other considerations such as elevation. Models bring a pretty
significant amount of QPF across the region, with potentially around
a half inch to an inch of QPF possible mainly along and east of I-29
by midday Saturday. Right now it looks like the area will see
primarily cold rain for the duration of the event. The exception is
the Buffalo Ridge area, including Marshall, Windom, and possibly
Brookings where temperatures may hover near or just below freezing
and the greatest potential for snow lies within our forecast area.
But given the difficult nature of forecasting temperatures within a
few degrees this far out, not very confident in snowfall amounts at
this point. My highest amounts are on the far northwest corners of
Lyon and Cottonwood counties in MN where amounts near 6 inches, but
amounts taper off very quickly to the southwest, so will hold off on
issuing any winter weather headlines at this point. The blended
forecast also created a bit more freezing rain that one would expect
given thermal profiles, so tried to minimize this concern, although
there may be potential on the tail end of the system for some
drizzle or freezing drizzle on Saturday morning.

The active weather pattern continues into the start of next week,
with southwest flow aloft directing several waves our direction.
Models coming into a better consensus with the timing and track of
these features. The active pattern supports likely pops for much of
the area by Sunday night into Monday. Much like the last several
system, temperatures will not be far from freezing. It looks like
rain will be possible during the daytime, while temperatures near or
below freezing at night will also keep the potential for snow in the


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1050 PM CDT Wed Mar 21 2018

Radar currently shows light rain showers in the KSUX vicinity, and
these will continue during the overnight hours. Surface
temperatures should stay warm enough that any light precipitation
stays liquid. Dry air in the near surface layer will likely limit
precipitation to sprinkles. Patchy fog is also possible tonight
around KHON and the Buffalo Ridge in southwest Minnesota. This
does not look to be widespread or dense, but may hinder visibility


MN...Winter Storm Watch from Friday morning through Saturday morning
     for MNZ071-072-081.



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