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FXUS63 KFSD 220146

Area Forecast Discussion
National Weather Service Sioux Falls SD
846 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 00Z TAFS through 00Z Thursday evening)
Issued at 645 PM CDT Wed Mar 21 2018

Mostly clear skies prevail overnight, the exception being in the
far southern parts of our area, around KSUX, where a mid-level
cloud deck could even produce sprinkles overnight. Dry air near
the surface should minimize any impacts to visibility. Patchy fog
is included for KHON, and Pipestone, MN, but given the surface 
pressure gradient overnight, any fog should remain localized and
not dense in nature.


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



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