Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 222308
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
608 PM CDT Sun Oct 22 2017

.SHORT TERM...(This evening through Monday)
Issued at 409 PM CDT Sun Oct 22 2017

160kt jet streak riding over Pacific coast ridging will begin to
punch out into the plains tonight, digging a significant trough
across the Northern Plains through Monday.  As main wave begins to
dig with PV gradient pushing through between 06z-12z, leading edge
will contain a mid-level frontogenetic band which has been
concentrating a few showers today.  Do not expect much with moisture
somewhat limited in depth and persistence, but isolated light
showers or sprinkles could begin to creep toward Highway 14 after
06z, and sink in a slowly dissipating manner heading southeast.
Additional precipitation is likely to occur during the midday and
afternoon on Monday as diurnal cycle meets up with trough axis
sliding rapidly southeast. Steepening lapse rates actually bring a
narrow CAPE profile, with temps through moist layer getting well
within efficient ice process ranges. Only the warmer near surface
layer looks to prevent surface ice presence, but still would not be
shocked that any isolated stronger cells could have a little graupel
in parts of southwest MN early afternoon. By late day, trough axis
passes, and main concentration of moisture begins to shear southeast
away so will see decrease in coverage late.

Despite all this, the main concern in the short term will be with
potential for very strong winds on Monday.  Winds will begin to
increase for a time immediately behind the surface boundary late
tonight, but the real increase is expected to show by mid to late
morning as start to steepen the low-level lapse rates and off-
surface gradient increases to 35 to 45 kts.  Even where there could
be a bit less gradient wind aloft toward parts of southwest MN and
northwest IA, the isallobaric support is maximized with 3-5 hPa/3h
rises moving across that area during the time of maximum diurnal
support during the early to mid afternoon.  A wind advisory has been
posted for the entire area late morning through the afternoon hours.

Tempwise, readings will remain fairly mild tonight with warmer
airmass and southerly flow ahead of the advancing boundary, then
with the mixing enhanced immediately behind the boundary, resulting
in 40s overnight.  On Monday, temps will likely reach maximums early
for most locations, especially with the advancing clouds and light
precipitation in the afternoon around southwest MN/IA Great Lakes
areas where cold advection will be maximized during the afternoon.
Likely to see many areas with steady or more likely falling temps.

.LONG TERM...(Monday night through Sunday)
Issued at 409 PM CDT Sun Oct 22 2017

Some brisk winds continue through Monday night and get a refresh
on Tuesday with deep northerly flow. Will likely stay just under
wind advisory most locations west of I-29, but will have to watch
southwest MN and northwest IA to see how deeply mixed it gets with
continued low-level cold advection slowly transitioning toward
neutral in the afternoon. A first solidly below normal day in
quite a while.

A little mid-week roller coaster in temps as a couple boundaries
pass through as another wave passes well northeast of the region, in
advance of the more significant change late week. Wednesday likely
to be a bit warmer than normal again. By Thursday, another strong
jet and amplifying trough will begin to dig across the northern
Plains.  This feature will be accompanied by yet another drastic
increase in northwest winds, potentially once again reaching
advisory criteria with 35-45 knots within the mixed layer.
ECMWF continues to waffle solutions somewhat between 00z and 12z
runs, becoming again a bit more progressive on the latter and closer
to both the operational GFS and the majority of ensemble members.
The end result is a continued trend toward a very cold and
potentially snow-laden forecast toward the end of the week.  While
it does not appear that dynamics will support any significant snows
in the immediate area, there will certainly be some flakes flying at
times from Thursday night through early Saturday, especially from
east central SD toward northwest IA. Would not be shocked to see
some dusting to inch amounts by the time all is said and done,
perhaps as far southwest as KFSD. GFS bears watching with its great
amplification of closed low and development of trowal toward south
central MN later Thu night into Friday which could enhance amounts a
bit more.  Highs likely to be reached early Thursday, and then it
will largely be a downhill ride right through early Saturday, with
just a few minor blips upward with help of late October sun angle.

Little alteration to conditions after Friday, with some disparity in
progression of features.  Should at least get a bit of moderation on
Saturday, and a bit further Sunday, still shy of normal, and likely
more than a solid freeze for all over the Thurs night-Saturday night
period for those nursing late season vegetation.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 549 PM CDT Sun Oct 22 2017

Gusty northwesterly winds are the main story as a cold front
moves through the area in the overnight hours. Models suggest the
development of LLJ at all terminals early in the morning. Strong
surface winds will persist through the early evening, with gusts
as high as 39 knots possible in the afternoon.



&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 10 AM to 7 PM CDT Monday for SDZ038>040-050-
     052>071.

MN...Wind Advisory from 10 AM to 7 PM CDT Monday for MNZ071-072-080-
     081-089-090-097-098.

IA...Wind Advisory from 10 AM to 7 PM CDT Monday for IAZ001>003-
     012>014-020>022-031-032.

NE...Wind Advisory from 10 AM to 7 PM CDT Monday for NEZ013-014.

&&

$$

SHORT TERM...Chapman
LONG TERM...Chapman
AVIATION...05



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