Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 261951

Area Forecast Discussion
National Weather Service Sioux Falls SD
251 PM CDT TUE JUL 26 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 250 PM CDT Tue Jul 26 2016

Tough forecast this evening as an outflow from the thunderstorms
earlier today in northwest South Dakota pushed into central South
Dakota and have spawned a few thunderstorms. A couple of the
updrafts interacted with an outflow dropping south and briefly
rotated for about 5 to 10 minutes. The storms will struggle to
spread east with slow storm motion as well as more stable air to the
east. Both low and high resolution models have really struggled with
set up today but the latest HRRR-EXP seems to be on track a little
more. It seems like development in central South Dakota north of
Chamberlain will be difficult as much more stable air has filled in
behind this convection, with the more unstable air across south
central SD. Suspect that this is the area with the best chance for
stronger updrafts into the evening. Severe not highly likely but an
isolated wind gust to 65 mph and hail possibly to half dollars will
be the main threat. A good chance that this diurnally driven
activity will continue to drift south and then attention will turn
to the weak incoming upper level wave, which should move into
central SD by 9z to 12z and into southwest MN and northwest IA by
about 15z to 18z. This will suppress the more unstable air towards
the Missouri River so will see a mid range chance for showers and
thunderstorms through the day with an increasing chance towards
Sioux City and northwest Iowa late in the afternoon. Deep layer
shear and instability both support an isolated threat for severe
with 60 mph winds and quarter sized hail the main threats.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 250 PM CDT Tue Jul 26 2016

Tough forecast for the Wednesday night time frame, with little model
agreement in terms of timing of the short wave.  NAM and Canadian
are a bit more progressive, shifting things east of the bulk of
the forecast area by 00z. The GFS and ECMWF are slower, with
lingering showers and storms east of I-29 through at least the
evening hours. Depending on which model one chooses, instability can
vary from 1000-2000 J/kg of CAPE.  With mid-level shear, could see
a storm or two approach severe limits supporting general to marginal
severe weather outlook.

Have continued to trend down pops for Thursday time frame.  Little
agreement amongst the models on Friday as short wave train moves from
northwest to southeast through the region.  Not much in the way of
instability with moist adiabatic lapse rates, but could see a few
scattered showers and thunderstorms.  Favored area based on the
trajectory of the short waves would be across the southwestern half
of the forecast area...mainly into south central South Dakota and
northeast Nebraska.

Temperatures look to mainly be below normal through Saturday, but
warm on Sunday through Tuesday as upper level ridge builds in and
southerly flow dominates.  Still could see some periodic
precipitation chances during that time frame, but is hard to predict
when and where.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1215 PM CDT Tue Jul 26 2016

VFR through the period. Isolated to scattered thunderstorms along
and west of the James River Valley through the evening, with the
chances expanding east through the night. Additional shower and
thunderstorm activity will remain possible through Wednesday
morning. Brief MVFR conditions will be possible within the
stronger thunderstorms.


.FSD Watches/Warnings/Advisories...


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