Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 231036

Area Forecast Discussion
National Weather Service Sioux Falls SD
536 AM CDT Wed Aug 23 2017

.SHORT TERM...(Today and Tonight)
Issued at 405 AM CDT Wed Aug 23 2017

Overall should be a fairly quiet day and night as a weak wave drops
south through MN. A 60 to 70 knot upper level jet will move into
southern MN while a weakness in the jet will be present across parts
of WY and MT. Between these two areas over southeast SD and northern
NE mid level moisture will increase through the day. Overall not
much of an increase, but enough to bring partly to mostly cloudy
skies from mid afternoon into the evening. Precipitation chances
will be minimal with dry air below the mid level moisture and
instability fairly nonexistent. Some hints of some minor elevated
instability near the Missouri River early in the evening but nothing
more than a couple hundred J/kg CAPE.

As for surface temperatures, the low to mid level temperatures will
be a couple of degrees warmer than yesterday so planning on keeping
highs about where the latest forecast had them, which were from the
upper 70s in southwest MN to the mid 80s in central SD. Lows will
not be as cool as this morning with a southerly wind of 5 to 10 mph
through the night. expecting mid 50s to lower 60s.

.LONG TERM...(Thursday through Tuesday)
Issued at 405 AM CDT Wed Aug 23 2017

Trough digging into the Great Lakes on Thursday morning will drag a
weak jet entrance through southwest MN and northwest IA early in the
day, but fairly good curvature to the flow should mean subsidence
will largely prevail, and the drier air below mid-level cloud deck
should minimize any precipitation threat. Persistence of warm
advection through the day could eventually spur an isolated shower
or thunderstorm toward the lower Missouri River valley, but anything
would likely have to be elevated with a deep weaker cap indicated
toward any surface-based activity, north of the synoptic warm front
across eastern Nebraska.  A weak wave moving out of the central
Rockies will move through the larger-scale ridge Thursday night
through Friday, enhancing the low-level jet further and allowing a
better shot at thunderstorms Thursday night, spreading north and
east into southwest Minnesota overnight. Not expecting any severe
storms with instability profiles fairly skinny and any effective
shear suffering at the hands of a distinct weakness in the mid-level

Persistent warm advection on Friday makes it hard to shut down any
smaller chances as the main gradient in lift pushes northward.
Should be quite a bit of residual cloudiness impacting temps,
otherwise it could get several degrees warmer than forecast,
especially south of I-90. With convergence boundary and upslope flow
into the western plains making a logical source region for
convection, will probably see a tendency for greater coverage of
late day activity initiate out west, especially with stronger
northern stream wave steaming toward ND.  This wave should
reinvigorate a weakened low-level jet Friday night, and will see
progression of storms with the wave eastward through Saturday. Again
does not appear to be a significant setup for severe storms, but the
persistence of the low-level jet and thin CAPE profile would bring a
slightly better possibility for some spotty heavy rainfall Friday
night into Saturday.  At this point, moisture does increase, but the
increase is limited by the tropical system near the TX coast
knotting up the return.  This was one period where some increase in
PoPs over the initial blend were warranted.

Later Saturday night into Sunday, the model suite suggests the
northern stream wave will begin to close off as it digs into
Minnesota, slowing up somewhat the low-level frontal boundary
and exit of precipitation on Saturday night. Will be apt to find
some instability showers/storms diurnally enhanced on Sunday through
areas near/east of I-29 closer to upper wave, and have had to keep a
small mention of showers through the eastern CWA even into Monday.
Finally, a surface ridge settles southward with heights rising
Monday night into Tuesday, for a quiet but seasonally cool period.
In general, most if not all temperatures during the longer range
period will continue to feature somewhat below normal readings.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 536 AM CDT Wed Aug 23 2017

VFR through the period.




LONG TERM...Chapman
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