Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 222034
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
334 PM CDT Tue Aug 22 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 334 PM CDT Tue Aug 22 2017

Northwest flow aloft will continue to dominate our weather through
at least Wednesday evening. High pressure will slowly build eastward
this evening, leading to some light to calm winds tonight. Have gone
slightly below guidance in anticipation of good radiative cooling
conditions. Also, the weak winds, along with lingering moisture from
Monday`s rain event, will lead to a chance for fog across the
forecast area. Luckily, decent mixing this afternoon has lessened
the amount of surface moisture and our chances of fog tonight.
Nonetheless, something to keep an eye on, especially in river
valleys.

Only chance of precipitation will be Wednesday evening as a small
wrinkle in the northwest flow approaches our western zones before
00z. Supporting a chance for rain will be some moist isentropic lift
west of the James River around the 310K and 315K surfaces. Several
GFS members and the EC put out a smattering of QPF in this region as
well. However, low level moisture will be rather paltry, leaving
only a small chance of measurable precipitation actually making it
to the ground. There is some MUCAPE out there as well, particularly
west of the Missouri River, so will put isolated thunder into the
small chances for precipitation.


.LONG TERM...(Wednesday night through Tuesday)
Issued at 334 PM CDT Tue Aug 22 2017

Limited chance for showers and thunderstorms Wednesday evening as
moisture return in the 700-800 mb layer results in a weakly unstable
environment.  Saturation is very shallow, so thunderstorm
development is very conditional, and even if showers were to
develop, there is a fair amount of dry air near the surface making
it questionable if moisture can reach the surface.

Southerly winds will increase throughout the day on Thursday ahead
of the approaching system.  The Gulf remains cut off initially with
tropical system rapidly intensifying off the east coast of Texas.
Because of the position of this system, it may limit the amount of
moisture transport northward this weekend. Still could see
shower/thunderstorm activity through the weekend as a series of
short waves pivot through the area. The initial leading shortwave
moves through the area on Friday night into Saturday.  Nice veering
wind profile, but limited amounts of instability.  Second wave
rotates into the region on Sunday.

Temperatures through the period remain nearly 5 degrees below normal
through the period.

Drier conditions develop early next week as surface ridge remains
across the Northern Plains.  Rex block is expected across the east
coast, leading to pleasant fall conditions lasting through at least
mid week.


&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1238 PM CDT Tue Aug 22 2017

VFR conditions expected through the period. Gusty winds will
impact primarily southwest Minnesota and northwest Iowa this
afternoon with gusts likely at SUX and FSD. Winds will decrease to
at or near calm tonight. Reduction in winds brings a conditional
chance for fog tonight at all 3 TAF sites as the amount of
lingering surface moisture from Monday`s thunderstorms will depend
on the amount of mixing this afternoon. Confidence in fog is not
large enough for inclusion at this time.


&&

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

$$

SHORT TERM...Ferguson
LONG TERM...BT
AVIATION...Ferguson/


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