Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 170552

Area Forecast Discussion
National Weather Service Sioux Falls SD
1252 AM CDT Mon Oct 17 2016

.SHORT TERM...(This evening through Monday)
Issued at 343 PM CDT Sun Oct 16 2016

Mid level short wave is currently moving across the Sioux Falls
forecast area, and will exit our far eastern zones by about 06Z
Monday. There is very abundant low level moisture at and below 850mb
along and east of the James River valley, which will move slowly
eastward through the evening hours. In addition, we have ample mid
and upper level moisture due to the wave, but a big dry layer in
between from 850-600mb. With a strongly veering warm air advection
profile, drizzle is certainly a threat late this afternoon and
evening across the eastern half of our area, and webcams indeed
showing drizzle occurring right now around Yankton and vicinity.
With the drizzle, including some threat for fog and also a small pop
for a light shower. But again, an actual shower may be tough to
realize with the dry layer above 850mb. Due to mid level instability
east of I 29, also still had to include a threat for a small chance
for thunder this evening in southwest MN and parts of northwest IA.

Will go ahead and issue a dense fog advisory for extreme southeast
SD, extreme northeast Neb and northwest IA late tonight and early
Monday. Timing is ripe for fog development due to the exiting wave
leaving a ton of low level moisture in place. And as the mid and
upper clouds exit, radiational cooling should take hold allowing
widespread fog to form. Future shifts will have to monitor this
closely to see if the dense fog potential migrates northward late
tonight. Overall however by very late tonight and early Monday, the
moisture near 925mb is drier when compared to this morning. So
despite the light winds coming up, the fog could scour out sooner
then it did this morning as it should be a bit shallower. Otherwise
Monday afternoon, still looking at a second short wave scooting
across the northern plains which could spawn a few TSRA in our
northern and eastern zones. Effective wind shear is limited and
mixed layer capes are not overly impressive with values around 500-
800 J/Kg, so thunder potential should stay in the general category.
For highs Monday, the GFS is a severe outlier with its 925mb
temperatures compared to the cooler NAM/GEM/ECMWF. Therefore
followed the latter 3 models for mixing potential which gives highs
in the upper 60s and 70s, no 80s. In addition, Monday may not be the
most pristine day in terms of clear skies with the second wave
ushering in more mid and high level cloudiness in the afternoon.

.LONG TERM...(Monday night through Sunday)
Issued at 343 PM CDT Sun Oct 16 2016

Precip chances will linger across our northeast into Monday evening
as the wave passes by the area, and continues to look like pretty
limited chances for any further rain through the remainder of the
forecast period. A southern stream wave slides across the central
Plains later Wednesday/Wednesday night, while a northern stream wave
drops into northern MN/western Great Lakes. Moisture availability
over our area is somewhat in question, so will only carry slight
chance to very low chance pops at best, and will keep confined to
areas south of I-90.

Temperatures through the period look to remain near to above normal
with the coolest day being Thursday behind a secondary cool front
that pushes south with the aforementioned northern stream wave. GFS
and ECMWF continue trending toward this cool-down being short-lived
though, with warmer air quickly building back in from the west for
Friday and Saturday. Model consensus has begun to latch on to this
and did not deviate too much for now. Another wave looks to swing
through during the latter half of the weekend. Better energy remains
north of our area, although could it scrape areas north of I-90 with
some light showers on Sunday. Temperatures will cool off a bit, but
expected to remain above seasonal norms.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1250 AM CDT Mon Oct 17 2016

Areas of IFR and below fog and stratus will plague portions of the
area through midday Monday.


SD...Dense Fog Advisory until 9 AM CDT this morning for SDZ067-070-

IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ001>003-

NE...Dense Fog Advisory until 9 AM CDT this morning for NEZ013-014.



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