Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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172
FXUS63 KFSD 150929
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
329 AM CST Wed Nov 15 2017

.SHORT TERM...(Today and Tonight)
Issued at 323 AM CST Wed Nov 15 2017

Non diurnal temperatures will be in play today and tonight. Cold
air will continue to surge across the area frontal boundary which
exited the area last evening. With skies clearing from west to east,
temperatures will continue to fall through mid to late morning,
before stabilizing midday. Skies will be mostly sunny for most
locations, however models do indicate some scattered cumulus
development late morning and midday mainly east of the James River.
Afternoon highs will only reach the mid 30s to mid 40s. Northwest
winds will be breezy through the late afternoon.

Surface high pressure slides eastward across the Plains tonight,
allowing surface winds to decrease, then turn east to southeast late
tonight. Mid and high clouds will also be on the increase from the
west late tonight. With southerly winds and clouds developing across
southeast SD, temperatures will hold fairly steady overnight after
dropping into the 20s this evening. Expect to see temperatures even
rising a bit late tonight mainly across south central SD.

.LONG TERM...(Thursday through Tuesday)
Issued at 323 AM CST Wed Nov 15 2017

Thursday and Thursday night: Longwave trough begins to swing
eastward from the Pacific northwest across the northern Rockies.
This will drive large scale pressure falls along the lee of the
Rocky Mountains, setting up a pretty stout pressure gradient across
the CWA. With winds atop the mixed layer around 30 to 45 knots, have
increased southerly winds across the forecast area to be in line
with MOS guidance. Currently expecting the highest gusts to be sub-
advisory level in the 30 to 40 mph range. With all the advection and
mixing going on, coupled with potential clearing in the sky cover
Thursday afternoon, have boosted high temperatures above model
consensus. Southerly gradient winds continue Thursday night and the
eventual increase in moisture aloft will support increasing cloud
cover as the night progresses. Have likewise raised lows above
guidance as well.

Friday and Friday night: What a few days ago looked like a
potentially interesting forecast has trended in the opposite
direction. Clear model preference now is for the aforementioned
longwave trough to focus the best mix of forcing and moisture to our
southeast, primarily over IA/WI/IL. Most guidance continues to keep
surface and low level temperatures mostly above freezing during our
slight chance at precipitation Friday night. This seems reasonable
given the long period of warm advection preceding precipitation and
the consistency over the past several model runs. Have gone with
mostly a rain event with some light snow possible on the back side
at night. With plenty of cloud cover expected followed by cold
frontal passage during the late afternoon, have held high
temperatures under consensus.

Saturday through Wednesday: Northwest flow regime takes over,
leading to only scant chances for precipitation. General
ECMWF/CMC/GFS agreement on a weak disturbance in the flow Sunday
night but, with high pressure building over the mid-Mississippi
Valley blocking return flow from the Gulf, moisture will be severely
lacking for precipitation. After this time, the typical model
disagreements on wave depth and timing take hold but one theme
emerges: not enough moisture for any mentions of precipitation.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1044 PM CST Tue Nov 14 2017

Occasional MVFR ceilings will gradually improve to VFR levels
through the overnight hours. Areas of fog developing behind the
frontal boundary, especially along Highway 14 and southwest
Minnesota could linger through 08Z. Gusty northerly winds return
on Wednesday morning with gusts to around 20 knots by late
morning into the afternoon hours.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...
LONG TERM...Ferguson
AVIATION...05



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