Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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791
FXUS63 KFSD 240347
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1047 PM CDT Sat Sep 23 2017

.SHORT TERM...(This evening through Sunday)
Issued at 349 PM CDT Sat Sep 23 2017

Very little has changed with the overall position of the longwave
trough over the West, with a downstream ridge firmly in place over
the eastern states. In the lower levels of the atmosphere, a
southwest to northeast surface boundary continues to stretch from
central Nebraska through southwest Minnesota. Warm, moist south
winds continue to the southeast of this boundary bringing hot and
muggy conditions to those in NW Iowa. In contrast, places like
Huron, SD have been cloud-covered throughout the morning and sit
under a shallow, much-cooler near surface air mass and northerly
surface flow.

Thunderstorms this afternoon have been firing northwest of the
surface boundary where the better dynamics exist, leading to
elevated thunderstorms. Limited wind shear and modest lapse rates
will continue to hinder thunderstorm strength, while the lack of a
surface connection also decreases the gusty wind potential.
Nevertheless, small hail and lightning will be threats with any
storms throughout the evening hours. To the southeast of the surface
boundary, scattered evening showers are likely as the boundary layer
destabilizes, but these storms are not expected to be severe.

Models show the frontal boundary and thunderstorms retreating
slightly to west overnight, which would keep areas east of a Yankton
to Brookings line fairly dry overnight. Areas west of this line will
continue to see low clouds and periodic showers & thunderstorms.
It`s not until a shortwave trough moves northward Sunday afternoon
and evening that the front again nudges eastward, bringing more
widespread chances for rain to areas south, southeast, and east of
Sioux Falls. high temperatures Sunday continue to show the stark
differences in low level air masses, with upper 70s and 80s east
of I-29, and much cooler 60s for Huron to Chamberlain.

.LONG TERM...(Sunday night through Saturday)
Issued at 349 PM CDT Sat Sep 23 2017

Rain Monday will be focused along the slowly-eastward-
moving boundary in NW Iowa and SW Minnesota. Afternoon thunderstorms
Monday will lack the instability of previous days, and are not
expected to be strong at this time. Surface temperatures will be
cool for most under the shallow Canadian airmass, with widespread
stratus clouds blocking the sun for much of the day.

On Tuesday the upper level jet finally pushes east and helps clear
the region of precipitation. For Wednesday through the end of next
week, sunny, dry, and cooler than seasonal average conditions
prevail.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1044 PM CDT Sat Sep 23 2017

The showers and isolated thunderstorms have retreated west and
should stay in central SD through the night into Sunday morning.
The surface cool front has shifted into southwest MN which will
bring a better chance for stratus farther east. Guidance showing a
lot of low visibilities under the stratus but not going to buy
into that just yet, although it really does not matter with the
IFR ceilings the main concern. By tomorrow afternoon into the
evening showers and thunderstorms will work from west to east with
new stronger development possible over northwest IA.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...VandenBoogart
LONG TERM...VandenBoogart
AVIATION...08



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