Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 280841

Area Forecast Discussion
National Weather Service Sioux Falls SD
341 AM CDT THU JUL 28 2016

.SHORT TERM...(Today and Tonight)
Issued at 340 AM CDT Thu Jul 28 2016

Fairly quiet weather expected through tonight, with relatively dry
low level flow east of surface ridge which will remain across the
western CWA. Just enough mid-upper level moisture around though,
along with subtle mid-upper level waves sliding through northwest
flow, to keep skies far from pristine. One such wave could trigger
spotty showers or an isolated storm in our far eastern counties from
Windom to Storm Lake during the afternoon/early evening, but expect
these would dissipate quickly with loss of daytime heating as wave
scoots east of the forecast area by 00Z. A second, somewhat stronger
wave is projected to scrape by our far southwest corner in south
central SD, although greater forcing focused much farther southwest
along low-mid level baroclinic zone this afternoon through tonight.
Will carry some low pops in these two areas, with thunder potential
in either location on the lower end given marginal instability.

Temperatures will be on the cool side of normal, with highs from mid
70s in our far east around Windom/Jackson, to lower-mid 80s through
the James and Lower Missouri River Valleys. Lows tonight should also
be quite comfortable in the mid 50s to lower 60s.

.LONG TERM...(Friday through Wednesday)
Issued at 340 AM CDT Thu Jul 28 2016

A bit of baroclinicity remains toward south central SD and barely
enough signal for lingering lift early in the day to suggest a
skittish shower or two with perhaps a rumble of thunder to start the
day, but soon enough larger scale forcing will become even more
meager between exiting wave and next weak upstream wave slated for
Friday night.  Likely to be a fair amount of lingering cloudiness
toward northwestern Iowa and vicinity fed by easterly component of
lower level flow fields. Thus, expect temps to struggle a bit and
have cooled off highs a couple degrees in much of northwest Iowa,
and lesser moving away from the area. Should be enough subsidence to
break up thicker clouds closer to the downstream side of lower level
ridge axis near/west of I-29.

Wave treks east and southeast through Friday night, but again will
struggle as it encounters drier and more stable trajectories toward
the lingering lower level ridge to the east, as well as the
stretching of energy falling into the Great Lakes trough axis.
Scattered precipitation will likely favor areas west of the James
River overnight, but then diminish pushing near/east of I-29 early
Saturday. Overall cloud cover should also gradually work toward
diminishing on Saturday, which should allow temps to nudge a few
degrees warmer most locations, despite very little change in air
mass.  Hardly enough elevated CAPE to matter at 400-800 J/kg and
expect a negligible severe weather threat through Saturday.

Saturday night finds synoptic warm front remaining well south across
Kansas, and surface ridge finally relaxing eastward enough to allow
a strengthening south to southeast flow overnight.  Late night,
should get a little boost in elevated theta-e advection as slightly
better mixed-layer aloft pushes into southeast South Dakota, and
have nudged up chances for a few elevated storms between the James
valley and I-29 late night. Again, severe threat would likely remain
very low with these storms.  Some concern about the subtleties of
the low-level moisture return, which could have impact with a little
fog toward northwest Iowa and lower Missouri valley locations, if
not a larger threat for late night stratus bloom across eastern
Iowa/Nebraska which will leak toward the southern CWA.  For now,
have increased clouds and will address any specific fog threat as
period approaches.

Challenge in the extended range remains timing of various smaller
scale disturbances which more along the largely zonal pattern along
the northern tier.  Sunday appears to find common ground in
continued rising heights and warming mid-level temps.  Most model
signals suggest as least a partial intrusion some lower clouds for
the early part of the day, especially from the James valley
westward. Otherwise, early day elevated storms will shift eastward,
but again should see decreasing effective coverage by midday as weak
upper wave abandons the area.  Some clouds will continue to impact
temps with highs in lower 80s east of I-29, but even any slowing of
warming in south central South Dakota with morning clouds will
likely give way to highs around 90. Sunday should be the start of
more uncomfortable dew point.

The western plains lee trough along with a persistent southeast
lower level flow should make this the focal area for late afternoon
or evening convective development Sunday night. While could see a
few storms survive eastward tracking along with subtle mid level
wave, would also looks for a small chance for elevated storms to
develop again along mid level thermal gradient and low level jet
from east central SD to northwest IA late Sunday night. Starting the
following work week, will see a fairly strong trough pushing by to
the north across southern Canada, driving a frontal boundary
southward into the area.  This front will provide the next decent
chance for precipitation, and will have to watch for severe storm
potential by Monday evening with heat and humidity providing much
increased potential instability, along with the stronger shear along
the southern edge of westerlies.  Could see some Monday afternoon
heat indices push to around 100 for the James and Missouri valley

Further out, in general the ECMWF is a bit quicker than the GFS
through next week, but GFS deviates strongly by reestablishing a
trough in the Great Lakes by Wed. and shows almost no consistency in
the ensemble members.  For now, have not strayed very far from
initialization grids, but did work to minimize some of the precip
mention for Tuesday and Tuesday night.  By later Wednesday and Wed.
night, could have another better opportunity for thunderstorms as
stronger troughing pushes through the northern Rockies and into the
northern plains, again with the risk of a few more severe storms.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1055 PM CDT Wed Jul 27 2016

VFR conditions are expected through the TAF period.


.FSD Watches/Warnings/Advisories...


LONG TERM...Chapman
AVIATION... is the U.S. government's official web portal to all federal, state and local government web resources and services.