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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
610 am CDT Monday Sep 22 2014

Short term...(today and tonight)
issued at 340 am CDT Monday Sep 22 2014

High pressure will shift off to the east today as an upper wave
approaches from the west. Should see mostly sunny skies...with
cirrus slowly increasing from west to east this afternoon. Pressure
gradient increases with the departing high...and southerly winds
will become blustery by afternoon along and west of the James River
with gusts up to around 30 miles per hour expected there. With southerly flow
and warm air advection aloft...probably will not see the best mixing
today...but still should see highs in the low to middle 70s. So overall
expecting a pleasant Monday across the region.

Conditions will deteriorate from west to east overnight as moisture
and forcing increase ahead of our next wave. Pretty good upper
support from the wave will move across the County Warning Area...and plenty of
moisture with precipitable waters around 2 Standard deviations above normal. Thus
thinking we will see scattered to numerous showers develop this
evening and slowly push east. Models generally in good agreement
with timing...with showers moving into south central South Dakota
this evening...approaching Interstate 29 by 12z. Instability is
pretty minimal...which should limit precipitation intensity and
thunderstorm potential. Thus generally looking at light to moderate
shower activity. Although do see some slightly negative Li values
with parcels lifted from 700 to 800 mb...thus should see a few
lightning strikes and pockets of heavier rainfall. Better chance of
the higher rainfall amounts...around or over a quarter inch through
12z...will probably be towards the Missouri River...where
convergence along the developing low level jet will be greater. This
is supported by model quantitative precipitation forecast and sref probability solutions.

Long term...(tuesday through sunday)
issued at 340 am CDT Monday Sep 22 2014

Upper low continues to approach the area on Tuesday with the band of
rain showers and isolated thunderstorms lifting into south central
South Dakota into the James River Valley Tuesday morning and slowly
shifting northeast through the day. With fairly sharp ridging
holding over the Mississippi Valley...there will remain strong
subsidence across our eastern third for much of the day. Very dry
low and middle levels will limit the eastward push of this
band...especially through early afternoon. Models suggest that as
the showers move east of i29 in the afternoon activity will become
more scattered with diminished moisture and middle level support as a
middle level wave lifts quickly northeast. With the upper low
meandering into the western forecast area in the
afternoon...additional scattered to isolated light rain showers will
again develop. Forecast soundings suggest enough weak middle level
instability for some isolated thunder mention...however the near
absence of shear will keep this activity of a weak nature. Highs on
Tuesday will be below normal across the board...only reaching the
middle to upper 60s.

The upper low continues to wobble eastward before gradually becoming
washed out under the large scale upper ridge on Wednesday. A few
lingering scattered shower across our southeastern third will
diminish by the evening. Persistent overcast skies begin clearing in
the west Wednesday afternoon...and should bring far milder
temperatures near 80 in the west...while the cloudy east will only
reach 70 or so.

Mild and pleasant weather returns for the remainder of the week with
southerly low level flow. Temperatures rebound to above normal
readings during the period...mainly in the 70s. Scattered clouds
will linger Wednesday night into Thursday across the southeast as
the upper low slowly dissipates...but the weather will be largely
dry. Elsewhere sunshine will be more abundant. Breezy southerly
winds develop Friday and Saturday.

&&

Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 605 am CDT Monday Sep 22 2014

Expecting VFR conditions at the taf sites today and tonight.
Patchy shallow fog out there this morning along rivers will
quickly dissipate. Clouds will increase tonight with scattered to
numerous showers and possibly a thunderstorm developing. This
activity is expected to stay southwest of the taf sites
tonight...but should be approaching all three around 12z. Where it
does rain tonight in south central South Dakota...will probably
see some MVFR visibilities in the steadier showers.

&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

Short term...chenard
long term...
aviation...chenard

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