Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 142001

Area Forecast Discussion
National Weather Service Sioux Falls SD
301 PM CDT Thu Sep 14 2017

.SHORT TERM...(Today and Tonight)
Issued at 356 AM CDT Thu Sep 14 2017

Shortwave trough moving northeast through the Dakotas will bring a
narrow corridor of moisture into the western CWA this morning. These
light showers should struggle as they move eastward and forcing
moves away. Nevertheless, will keep a low PoP to the James river
through mid-morning.   Further south, strong isentropic lift on the
315K sfc across eastern Nebraska should promote mid-level clouds and
a few showers that should stay south of the CWA.

Today: Model consensus brings a sfc trough slowly southeast through
the day, perhaps stalling it along a Lake Andes to Brookings line by
this afternoon and bisecting the CWA by the evening. The northeast
advection of an EML should prevent much in the way of convection
later this afternoon.  Temperatures will again climb nearly 10 or
more degrees above normal.  Have bumped winds across NW Iowa and
adjacent areas of NE/SD/MN this afternoon with mixing up to 800 mb
supportive of downward momentum transfer of wind gusts 25-30 knots.
Only other thing to watch would be for potential of wildfire smoke
to linger in behind the frontal boundary over central SD this
afternoon and evening. HRRR simulations do support some smoke moving
SE, but no real confidence on whether or not it will be thick enough
to impact visibilities.

Tonight: Have backed off on PoPs during the first half of the
overnight hours, and introduced a low end PoP by midnight as models
begin showing a warm advection signature within the 700:600mb layer.
Whether or not moisture is sufficient is in question, but could see
a decent amount of virga or very light showers focused primarily
along or southeast of the surface boundary from Lake Andes to
Marshall and southeastward.

.LONG TERM...(Friday through Wednesday)
Issued at 356 AM CDT Thu Sep 14 2017

Friday night the area will be under broad low and mid level warm air
advection as a wrinkle in the southwest flow aloft moves through.
This should allow showers and a few thunderstorms to develop with
the better chances east of the James River. Instability and shear
are strong enough to support a few severe storms but organized
severe weather is not expected. Temperatures should stay very warm
ahead of the incoming cool front with lows across northwest IA in
the mid 60s.

Saturday will see a continued chance for showers and thunderstorms
but again, not expecting any organized activity. Suspect that most
of the area will be dry until late afternoon when a chance for
thunderstorms, a few severe, will occur over parts of northwest IA
and southwest MN. Instability a little better but shear still very
marginal so only isolated severe storms expected. Highs on Saturday
will range from the lower 80s near Storm Lake to 60 to 65 from Huron
to Chamberlain.

While Sunday should prove to be the coolest day overall, light winds
will allow for a pretty nice day as highs climb into the upper 60s
to lower 70s.

Monday will have southerly return flow set up as surface high
pressure drifts east. A jet max across the southern Rockies
extending towards the central Plains will bring a small chance for
showers and thunderstorms to locations south of Interstate 90 as
warm advection in the mid levels focuses in that area.

Some agreements and disagreements for Tuesday through Thursday in
the models but overall confidence is decent. A strong trough will
dig into the west coast and then across the Rockies. All of the
models agree with this overall pattern. The big difference is the
speed at which the GFS swings out the initial jet max which is quite
a bit faster than the ECMWF and Canadian. This would bring a better
chance for showers and thunderstorms Tuesday night into Wednesday
with winds turning to the west. The Canadian and ECMWF are much
slower and have the area deep into the southerly flow. In fact if
the pattern evolves close to the Canadian/EC we may have some record
warm lows on Wednesday morning in the upper 60s to lower 70s. Not
quite confident enough yet to go that warm, but the potential is
there. Nothing easily timetable at this time partially due to the
fact that this is day 5 through 7 and mostly because the models are
still a little less agreeable, but for now siding with the


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1218 PM CDT Thu Sep 14 2017

VFR conditions are expected this afternoon and evening, with breezy
south winds expected at airfields east of I-29. From 15/0600z, sites
west of I-29 could see a few showers, and perhaps a weak
thunderstorm, but these would be isolated in nature.




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