Area Forecast Discussion
Issued by NWS Sioux Falls, SD

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

FXUS63 KFSD 151720

Area Forecast Discussion
National Weather Service Sioux Falls SD
1220 PM CDT Sat Oct 15 2016

.SHORT TERM...(Today and Tonight)
Issued at 411 AM CDT Sat Oct 15 2016

Larger scale flow for non-resident pheasant opener today finds a
wave moving just north of the international border through a
slightly ridgy zonal pattern. Ahead of the wave, strong low level
jet continues across the CWA with strong winds especially along
higher terrain which has shown gusts from 35 to nearly 45 mph at
times. Frontal zone associated with the upper level wave has now
pushed to just west of the James river valley by 08z. Main
challenge today will be dealing with mass of stratus field
evolving at the present (08Z) across eastern Nebraska, northwest
Iowa and into southwest Minnesota.

See no reason that low level jet will not continue to drive stratus
north/northeast through the CWA early this morning. Challenge will
be to determine how far west stratus can spread before a greater and
greater westerly component begins to shunt the area to the east. NAM
is outlier on the western extent of which it has been quite
incorrect on through the current time.  If one ensembles several
runs of the HRRR/experimental HRRR/RAP and WRF, this would suggest a
western boundary somewhere near I-29, a bit more westward through
the Missouri valley. So far there has not been a hint of any
visibility drop nor drizzle signature on radars under the stratus
canopy, but given the shear would not be shocked to get patches of
drizzle or fog develop toward daybreak with a favor shown toward the
Buffalo ridge and extension through parts of northwest Iowa.
Progression of weak frontal boundary across the CWA will
increasingly push the stratus more and more into areas toward the
eastern tier of Iowa counties from the Iowa Great Lakes to Storm
Lake by early afternoon, and out of the CWA in the afternoon. While
winds will not be terribly strong behind the front, it will set up a
good mixing environment with weak cold advection, which should drive
temps mostly into the 70s today.  One area to watch is how much the
stratus period impacts readings across northwest Iowa, but even
there, temps and dewpoints are in the lower 60s at present, and can
only work upward from there.

Tonight, weak high pressure will drop winds, and will not take long
for weak flow to pick up a south to east component. A bit of lower
level moisture hangs on around southern portions of northwest Iowa,
and with weak flow could be prime for redevelopment of lower clouds
and fog later in the night, so have added in areas of fog,
especially for highway 20 into the lower Missouri valley.

.LONG TERM...(Sunday through Friday)
Issued at 411 AM CDT Sat Oct 15 2016

Sunday will be warm and breezy as low pressure aloft moves across
the North Dakota/Canadian border. This will bring the increasing
southerly flow as well as increasing high clouds. The nam and GFS
are indicating that stratus may be a problem, especially across
southwest Minnesota and northwest Iowa as southeast flow in the low
levels increases. Will generally have 70s in most locations.

Sunday night upper level support swings by to the north and could
spark a shower east of the Buffalo Ridge on Sunday evening but
chances will be minimal. With a warm air mass in place lows will be
mild and in the 50s.

Monday a tough call on temperatures and small precipitation chances
as models not very agreeable on location and strength of jet max
moving through. Lowered highs just a touch along and north of
Interstate 90 as the potential to remain in easterly flow appears to
have increased which will limit mixing. Highs 70 to 75 north of I-90
and 75 to 80 south. Will keep a small chance for showers north of I-
90 Monday night as forcing along and ahead of the wave may allow fro
development of showers.+

Tuesday through Friday will see a trough of low pressure move from
the Rockies onto the plains by Wednesday night. After the passage of
the trough drier northerly flow sets up so no precipitation chances
Thursday or Friday. However there will be a chance for showers south
of I-90 Wednesday and Wednesday night as the main upper level
support passes by to the south. Temperatures will generally be
pretty cool with highs in the 60s Tuesday then 50s Wednesday through


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1220 PM CDT Sat Oct 15 2016

Lingering MVFR stratus mainly in northwest Iowa expected to clear
most areas through the afternoon as cool front moves into the area
from the northwest. Exception may be around KSLB, where boundary
will hang up and allow stratus to persist into the evening. Weak
flow and stubborn low level moisture in vicinity of the boundary
should allow for areas of fog/stratus to redevelop overnight into
Sunday morning. This expected to initially impact areas south of
US Highway 18 and east of KYKN, including KSUX late tonight.
However, as low level flow turns more southeast-south, the low
level moisture could be drawn northward toward I-90, bringing the
potential for MVFR ceilings into KFSD late in this TAF period.




SHORT TERM...Chapman
AVIATION...JH/MJ is the U.S. government's official web portal to all federal, state and local government web resources and services.