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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
1051 PM CDT Friday Aug 28 2015

issued at 943 PM CDT Friday Aug 28 2015

So changes to our fog forecast for late tonight and
Saturday morning. However...stratus is hanging tough in our
northwest Iowa well as the southern parts of southern
Minnesota. Therefore based on the 00z NAM 925mb relative humidity field...slowed
down the exit or evaporation of the clouds in our southeast zones
late tonight. In fact deep in our southeast area around Storm Lake
and Cherokee...the stratus may have trouble clearing out tonight.
Therefore it is a question mark what this stratus will do to the
potential fog in those locations. If the stratus hangs on in
northwest Iowa...that could keep fog from forming. But overall the
current fog forecast still looks good with an emphasis on the
areas which received the heavy rain Thursday and Thursday night.


Short term...(this evening through saturday)
issued at 357 PM CDT Friday Aug 28 2015

System shifting south and east of the area leaving behind a fairly
humid and cool air mass. After the diurnally driven cumulus
dissipates this evening...will be a bit later in northwest
Iowa...clear skies...decreasing winds and a very wet ground in some
locations should lead towards areas of fog. Will not issue a dense
fog advisory but suspect that there will be a decent chance at
seeing one in the morning. Temperatures will fall into the middle to
upper 50s by Saturday morning.

After shaking off some morning clouds and fog suspect that Saturday
will end up as a very nice day. Not much wind and partly cloudy skies
with temperatures from the upper 70s to middle 80s. Some slightly
warmer readings towards central South Dakota where Chamberlain could hit 90.

Long term...(saturday night through friday)
issued at 357 PM CDT Friday Aug 28 2015

Fog potential appears to be high once again Saturday night across
the area with light winds and surface moisture continuing to linger.
Added mention of fog and began to increase cloud cover...but will
likely have to continue to nudge sky up with future forecast

Appears it will be a struggle to mix out the moisture and warm the
surface across at least the eastern half of the forecast area on
Sunday. Have lowered temperatures in the east...but if stratus is as
persistent as model sounding show...may have to continue to lower
highs on Sunday.

Thereafter...appears to be a warm and relatively quiet week as upper
level ridge builds from the Desert Southwest into the northern
plains. By middle to latitude portions of the week...a large upper low
across the Pacific northwest tries to translate east...with a few
leading shortwaves embedded in the southwest flow aloft. Timing is
really ill basically removed probability of precipitation until Friday when
timing of a front is somewhat consistent in the models.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1047 PM CDT Friday Aug 28 2015

MVFR to IFR stratus will prevail across northwest Iowa for much of
the rest of tonight impacting the ksux taf site...who may waver
between lower end MVFR and upper end IFR. NAM humidity time
sections and soundings suggest that the stratus may erode close to
09z at ksux...but this will be monitored. If it does erode...then
fog is a certainly a potential late tonight and early Saturday
morning. Fog could also occur during the same time frame at kfsd.


Fsd watches/warnings/advisories...
South Dakota...none.


short term...08
long term...

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