Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 261201

Area Forecast Discussion
National Weather Service Sioux Falls SD
701 AM CDT TUE JUL 26 2016

.SHORT TERM...(Today and Tonight)
Issued at 401 AM CDT Tue Jul 26 2016

Large scale pattern this morning more or less a zonal mid-level flow
across the northern plains, with a couple of weaker disturbances
back toward northwest South Dakota and southwest Montana which will
be traversing the region through tonight.  Leading wave has kept a
bit of vigorous convection going along the northern SD border on the
nose of 35-40 kt LLJ through the night, but other than weaker cells
moving toward central SD which could limp into KHON area during the
early to mid-morning, not likely to see much activity well through
the day.  Focus for storms will remain largely near the frontal
boundary as it slowly sinks southward from a southeast ND to
northwest SD line - remaining north of the CWA through the day.
Large scale warm layer aloft will shoot out ahead of the approaching
waves ahead of the advancing frontal boundary, and somewhat limited
return of low level moisture should mean it will be enough to
effectively cap the environment through the day ahead of the frontal
convergence.  With warm push at lower levels squeezing ahead of the
boundary, could see zone of temperatures push into the lower 90s
from south central SD toward east central SD and toward the KMML
area this afternoon, with generally mid-upper 80s to the southeast.

Montana wave will be pushing into western South Dakota by evening,
and looks to be vigorous enough to initiate convection over the
western and northern portions of the state by very late afternoon or
early evening.  Lower level southerly flow does weaken somewhat by
late day, and this will decrease shear potential through the 0-1km
layer heading into the evening, and also keep 0-6km shear on the
order of 40-45 knots. Orientation of shear vectors again suggests
that storms should be more linear by the time they approach the
lower Brule areas in the evening.  Large amounts of DCAPE would put
a good weight into the damaging wind bin for severe weather threat
mainly this evening, generally southwest of a Wessington Springs to
Tyndall line where a more organized system is of greater likelihood.
A more isolated threat would exist as far east as MML-FSD-SUX,
perhaps marginally large hail but again more likely wind.  Best
elevated lapse rates appear to remain across the southwest half of
the CWA through the night, and even with wave sliding across the
area during the night, tendency for stronger storms to settle with
more of a southeastward/southward tracking through the evening could
see storms tend to dissipate or weaken as they approach the mid I-29
corridor later in the night.

One potential fly in the ointment would be the location of the ridge
axis this morning, and will have to watch light wind locations for
some potential patchy fog in areas from around KSUX eastward to KSLB.

.LONG TERM...(Wednesday through Monday)
Issued at 401 AM CDT Tue Jul 26 2016

Wednesday continues to look unsettled as shortwave energy moves
through the region.  There should be a good deal of scattered
showers and a few thunderstorms to begin the day well ahead of a
surface boundary lagging back towards central South Dakota. The
big question is how long this activity will last, and how quickly
downstream areas from convection and areas just ahead of the
advancing front can destabilize later in the afternoon. While the
low-lvl lapse rates are somewhat questionable, cooling
temperatures aloft do indicate steepening lapse rates in the
afternoon, yielding MLCAPE values upwards of 1500-2000 J/KG. Shear
however remains somewhat marginal, which could limit the overall
severe weather potential.

Scattered convection will move southeast through the evening hours,
and latest guidance has trended significantly drier for Thursday
and Thursday night. The only fly in the ointment to an otherwise
pleasant day on Thursday will be a low end risk for scattered
diurnal based storms in NW Iowa Thursday afternoon.

We`ll begin to see the next shortwave move into the Plains by
Friday, and this wave may bring higher rain chances to the local
area by Friday night into Saturday. The general trends would favor
dry conditions for Sunday through Tuesday as mid-lvl ridging

Temperatures through the medium range will average near to below
normal for Wednesday through Saturday. Temperatures by Sunday and
into next week will trend above the seasonal normals with heat
index values pushing 100 degrees once again.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 700 AM CDT Tue Jul 26 2016

VFR conditions will prevail until convection develops in central
South Dakota late afternoon and early evening. Convection will
focus mainly west of I-29 through the TAF period, and will likely
contain some brief MVFR conditions. A few storms toward south
central South Dakota could be severe during the evening, featuring
primarily a damaging wind threat.


.FSD Watches/Warnings/Advisories...


SHORT TERM...Chapman
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