Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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373
FXUS63 KFSD 251732
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1232 PM CDT SUN SEP 25 2016

.SHORT TERM...(Today and Tonight)
Issued at 317 AM CDT Sun Sep 25 2016

An upper level trough continues to swing across the Northern
Plains very early this morning, with the surface cold front
presently situated along the Interstate 29 corridor. Still seeing
showers and isolated thunderstorms out ahead of this feature
through parts of southwestern MN and northwestern IA. The frontal
boundary should be east of our CWA by 12Z with showers coming to
an end. Otherwise, much drier air filters into the region with dew
points falling into the 30s and 40s by late afternoon. In
addition, strong cold air advection will occur with the passage of
the front, and with steep low level lapse rates and increasing
winds aloft it will be a windy day. Winds at the top of the mixed
layer are not too extreme, remaining in the range of 35 to 40 kts,
so think we will stay below Wind Advisory criteria. An area low
clouds presently over western and central SD in association with
some trowaling behind the exiting system will swing across our CWA
during the day. It still appears that some sprinkles will be
possible north Interstate 90 in the afternoon with this moisture,
though removed bona fide pops with models trending drier. It will
be drastically cooler today, with readings a good 10 to 20 degrees
cooler than yesterday, with highs remaining in the 60s.

Clouds clear out tonight with winds slowly dropping off as surface
ridging nudges eastward into the Northern Plains. Do think that
winds will remain just strong enough to prevent temperatures from
completely bottoming out in the cool airmass, though will still
reach normal levels for this time of year - in the lower to mid 40s.

.LONG TERM...(Monday through Saturday)
Issued at 317 AM CDT Sun Sep 25 2016

Large trough digging in across the northern Great Lakes will keep
the area in a mixy northwest flow through Monday. Still 20 to 30
knots of wind available to mix down despite a weakening of the near
surface gradient by late day, so will again be breezy to windy. Such
a dry airmass that other than brief shards of ragged stratocumulus,
would expect little more than a few higher clouds. Highs will vary
from mid 60s to lower 70s, warmest through the Missouri river valley.

Loss of mixing will set up a swift drop in winds outside parts of
southwest Minnesota and around the Iowa Great Lakes where wind
decrease will be a bit more gradual.  Very dry air mass in place and
with surface ridge building in to areas near/west of I-29, expect
some lows in the upper 30s. Generally lower 40s elsewhere.

Midweek period Tuesday through Thursday will set up to be pretty
pleasant across the area, featuring fairly large diurnal changes due
to dry high pressure across the area along with plenty of daytime
sunshine.  There is some difference on the larger scale pattern with
the EC/Canadian holding on to more amplified Great Lakes troughing
into Thursday morning, holding back progression of the surface
ridge, and being slightly slower on moderating temperatures.  GFS is
a bit more progressive with features, starting warming a bit sooner.
Will have to watch and see if secondary wave dropping into trough on
Tuesday night/early Wednesday is enough to hold wave up per slower
solution subset, but for now have nudged temps both day and night
down just a bit east at least Wed and Thu.  May need to nudge some
lows closer to 40 degrees in the east on Wed/Thu as well if slower
solution evolves.

Differences in upper pattern begin to allow spreading of small
precipitation chances into the region starting later Thursday night
and continuing through Friday night, but much of this again reliant
on GFS allowing more progression to trough energy into the northern
plains ridging.  Temps will settle into the 70s/50s during this
period, meaning more slightly above normal readings.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1229 PM CDT Sun Sep 25 2016

Lower end VFR to upper end MVFR cloud cover will slowly erode from
west to east across the forecast area this afternoon and evening.
In addition, northwesterly winds will frequently gust to 25 to 30
knots this afternoon. By early evening, all locations will be VFR
with subsiding winds. Clear skies will prevail overnight and into
Monday.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...JM
LONG TERM...Chapman
AVIATION...MJ



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