Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 182312

Area Forecast Discussion
National Weather Service Sioux Falls SD
512 PM CST Sat Feb 18 2017

.SHORT TERM...(This evening through Sunday)
Issued at 309 PM CST Sat Feb 18 2017

Another night with lows at or above seasonal highs for this time of
year.  Surface high pressure will shift off to the east with
southerly flow returning to the region.  Could see some radiational
fog develop overnight near the I-35 corridor.  easterly component of
the low level winds may try to expand the western edge of the fog
into the far eastern portions of the forecast area in northwest Iowa
and potentially southwest Minnesota. Mid level clouds may limit the
potential on how far fog expands back to the west. Expect the
impacts to be east of any TAF sites.

Southerly winds increase throughout the day on Sunday. With another
surge of mild air across the region, have raised highs towards the
warm side of guidance.

.LONG TERM...(Sunday night through Saturday)
Issued at 309 PM CST Sat Feb 18 2017

A pair of system will impact the region in the extended. The first
system arrives Sunday night, as increasing low level moisture, cloud
cover and southerly winds build ahead of the system. Trough tracks
east through the Plains into Monday afternoon, directing a cold
front through the forecast area during the daytime. Scattered
showers form ahead of the front late Sunday night, becoming more
numerous east of I-29 on Monday as the main lift and forcing
arrives. With negative LIs and weak elevated instability developing,
will keep mention of isolated thunderstorms going, with thunderstorm
chances increasing ahead of the front in northwest IA and southwest
MN Monday afternoon.

Rain showers exit to the east by early evening on Monday, with
breezy northwest winds behind the front quickly diminishing and
shifting back to the west or southwest overnight. Zonal flow sets up
on Tuesday with dry conditions and near record warmth resuming. With
little if any cloud cover expected, and 925mb temperatures in the
lower to mid teen Celsius, highs on Tuesday should easily reach the
60s and may even breach 70 in the Missouri Valley. Nudged highs
warmer a few degrees above the SuperBlend.

Wednesday will be somewhat of a transition day, with a wave tracking
through the northern Plains. Another front quickly races through the
area, but aside from some increasing mid or high clouds, should have
little impact on the region. Temperatures will be slightly cooler,
with highs in the mid 50s to mid 60s. This will lead into a return
of southwest flow aloft ahead of the next, more significant system
impacting the region late week.

Broad trough digs into the Intermountain West midweek, then tracks
east into the western Plains on Thursday. Light rain will spread
eastward across the region in the warm sector late Wednesday night
into Thursday morning. The models still show some major differences
in where the thermal boundary initially sets up, with the GFS some
200 miles north of the ECMWF. Precipitation becomes more widespread
on Thursday with the upper low deepening over the central Plains
into Thursday night. The ECMWF remains strongest, with a slower and
more southerly track than the GFS, while the GEM is weaker than the
ECMWF, but also following a more southerly track. With a more
southerly track, precipitation is increasingly likely to transition
to snowfall Thursday night and Friday. However, there still remains
a great deal of uncertainty in the track of this system, and
therefore cannot pinpoint any snowfall amounts at this time. Very
gusty winds winds will also be a concern as this system increases in
strength Thursday night and Friday.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 512 PM CST Sat Feb 18 2017

VFR conditions will prevail through the period. Light southeast to
south winds tonight will increase from the south on Sunday, with
occasional gusts to near 25kt possible Sunday afternoon.




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