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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
403 am CDT Thursday Jul 10 2014

Short term...(today and tonight)
issued at 403 am CDT Thursday Jul 10 2014

Complex forecast today into tonight...with pretty large model
spread. Expect good large scale forcing for ascent this afternoon
into the overnight as a shortwave moves across the area. Thus
thinking at the least we see increasing clouds...making it a partly
to mostly cloudy day. Should see enough heating to still get highs
into the low to middle 80s most areas. Will be breezy as well...with
southerly winds likely gusting up to around 30 miles per hour. With the winds
staying breezy and likely cloud cover...lows tonight will be on the
mild side...generally middle to upper 60s.

Precipitation chances are more uncertain...with a noticeable
difference between the high resolution convection allowing models
and the the global models. Thinking we remain capped from surface
based convection through the daylight hours. However as forcing from
the wave increases...the threat of elevated convection may exist by
afternoon and evening. Focused these chances around Highway 14 and
points this is where forcing should be greatest and the
middle level cap weakest...and also where the European model (ecmwf) and GFS develop
quantitative precipitation forecast. High res models do not show this activity...likely due to a
stronger cap and less moisture. Thus these storms actually forming
remains low confidence...but given the forcing and quantitative precipitation forecast signals from
the European model (ecmwf) and GFS...felt chance probability of precipitation were warranted.
Elsewhere...good agreement among the hi res models that more surface
based convection could get going by late afternoon across southwest
South Dakota and northeast Nebraska...and move east towards Gregory
County. With better instability in the west and decent shear...a
severe threat would exist with this activity. Not thinking it would
move into our County Warning Area until around 03z at the earliest...and would
likely be in a weakening state. Thus the Storm Prediction Center slight risk area looks
pretty good...just clipping the southwest corner of the County Warning Area.

Low level jet increases even more tonight...which may help trigger
elevated convection across a good portion of the County Warning Area. Good signal of
this in the GFS...European model (ecmwf) and Gem quantitative precipitation forecast outputs. GFS seems to be a fast
outlier though...and think most of this should not develop until
after 06z. A bit worried by the lack of convective coverage in the
high res models. This again seems to be due to more of a middle level
cap and less low level moisture advection. So even tonights activity
is in question...but did not feel confident enough to change probability of precipitation
much. So will keep likelys going over most of the County Warning Area...but day shift
will have to reevaluate. Severe threat seems low with this activity
with instability on the weak side. Could be just enough instability
and shear to result in a few stronger storms again agree
with the low probabilities in the Storm Prediction Center outlook.

Long term...(friday through wednesday)
issued at 403 am CDT Thursday Jul 10 2014

Model differences increase from Friday into Saturday. All models
show basically two boundaries which will affect the area. The
first will set up between I-80 and the South Dakota/NE border on Friday. The
European model (ecmwf) and the GFS to a lesser extent have shifted this boundary
farther north than previous runs. The second boundary is a cold
front expected to set up across northern South Dakota by Friday afternoon. The
NAM is fastest bringing this boundary south. Given the progression
of waves moving across South Dakota...the rapid southward movement seems
unlikely and the slower movement of the European model (ecmwf) and Canadian Gem
seems more reasonable and was followed for this forecast in
general. While precipitation probabilities are generally 30 to 50 percent
for any one 12 hour period...what does seem certain is that most
places will see at least some rainfall between Friday morning and
Sunday morning.

On Friday morning...any convection remaining from Thursday night
convection should be east of I-29...primarily in northwest Iowa...and exit
during the morning. As another wave moves into western South Dakota during the
afternoon...the low level jet will back to south and begin to
overrun the boundary sitting across Nebraska. There will be a lot
of cloud cover so temperatures will only be in the middle 80s but
dew points are likely to be around 70 resulting in MLCAPES from 1500
to 2000 j/kg. 0 to 6 km bulk shear is between 25 to 30 kts. This
would favor more multicellular convection with a few of the
strongest updrafts able to support quarter size hail in the late
afternoon and evening near the Missouri River. Expect that
convective initiation will be late in the afternoon and more
likely in north central Nebraska so generally have a slight
chance. The second area where storms may develop is along the
boundary in northern South Dakota. Temperatures will be warmer with more sun but
there will also be less moisture so again...only have a slight
chance late in the afternoon. This wave comes through Friday night
and with the interaction of the low level jet and boundary in
Nebraska...there should be thunderstorms near the Missouri River
and into west central Iowa. The uncertainty is how far north the
convection will get. For that reason kept probability of precipitation between 30 and 50
percent in the Missouri Valley and northwest Iowa. There is the potential
for some heavy rainfall with these storms. Farther north...expect
convection will struggle once daytime heating ends so only have a
slight chance in the evening. However...a third wave will approach
central South Dakota after 06z. The European model (ecmwf) and Gem show more
convection developing with this wave and have probability of precipitation increase west
of the James River at that time.

On Saturday...the third wave will move across the forecast area. As
noted above...followed the European model (ecmwf)/Gem which shows rain spreading
across most of the area on Saturday. Therefore expect skies to
generally be cloudy much of the day with scattered thunderstorms.
The exception may be portions of SW Minnesota where enough low level dry
air combined with the southeastward movement of convection will
keep the convection to the south. With all of the
clouds...temperatures will be in the upper 70s to lower 80s which
will really limit any instability so severe weather is not
anticipated. Because of some uncertainty in how fast the
precipitation will move east of the area Saturday did keep a
slight chance of thunderstorms into Saturday across the entire
with a chance in northwest Iowa...although many areas will see
rain end by late Saturday afternoon.

In the extended...Sunday through Wednesday...the main story
continues to be the unseasonably strong upper low forecast to
become centered over the Great Lakes. All models now have the
front moving through Sunday night with unseasonably cold air over
the area through Wednesday. Sunday will be the warmest day of the
period with highs into the 80s. As the front approaches a few
thunderstorms may develop but instability is marginal with MLCAPES
1000 j/kg or less. If enough warm air can move in ahead of the
front as the GFS shows...highs could approach 90 in the James and
Missouri valleys. For now kept highs in the lower to middle 80s which
is closer to the consensus of GFS...Gem and European model (ecmwf). After the front
GOES through...highs will fall 10 to 15 degrees from Sunday with
60s and lower 70s expected both Monday and Tuesday. Monday will
also be quite breezy and any sun Monday morning may produce at
least isolated showers in portions of SW Minnesota. High pressure will
move over the area on Tuesday night and Wednesday. Currently have
lows in the lower to middle 50s but if it GOES clear with light
winds...record lows in the middle 40s may be challenged in a few


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1039 PM CDT Wednesday Jul 9 2014

VFR conditions are expected to dominate through the taf period.
Light southeasterly winds overnight will pick up around 15z on
Thursday morning. Scattered convection may develop across portions
of the area on Thursday afternoon and evening...though confidence
is low with regard to the activity affecting taf sites so left out
of the tafs.


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


Short term...chenard
long term...schumacher

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