Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 231133

Area Forecast Discussion
National Weather Service Sioux Falls SD
533 AM CST Sat Feb 23 2019

.SHORT TERM...(Today and Tonight)
Issued at 358 AM CST Sat Feb 23 2019

The wave and favorable right entrance region of the upper level
jet (along with some intruding instability) that brought this
evenings snowfall has moved off to the northeast. In its wake,
forecast soundings continue to show a saturated lower atmosphere
below the ice growth zone with subtle signs of lift. For this
reason, will continue to carry mention of patchy freezing drizzle
until about mid morning, although reports of impacts thus far have
been minimal and any freezing drizzle that falls may land on snow
covered surfaces, further limiting its impacts.

By this afternoon, all focus will be on the large upper level wave
currently visible on WV satellite imagery exiting the desert
southwest. Deterministic and ensemble model guidance continue to
remain in fairly good agreement in the surface low tracking from
south central KS into northwest MO by this evening and then into
southern WI by tonight. As it does so, an area of mid level
frontogenesis will slide from west to east thru central and
eastern SD and may bring some light snow this afternoon before the
main swath of precipitation swings in from the southwest across
our southeast quadrant counties. Snowfall over our NW IA counties
could be fairly heavy at times later this afternoon and evening
with favorable EPV* values and good lift in the dendritic zone.
SREF probabilities of 1 inch per hour rates also highlight this
area. The surface low pulls far enough east (deepening as it does
so) to pull the snow with it by late tonight.

Snow Amounts: Still expect a sharp gradient in snow amounts on the
north side of this system and thus a small shift either northwest or
southeast could have fairly drastic impact on snow amounts for any
one given area. This idea is further displayed in SREF and GEFS
plume diagrams from locations on the northern periphery with
nearly a 6-10 inch spread in some locations. For now, around an
inch of new snow is expected from roughly Yankton to Sioux Falls
to Marshall, with 1 to 3 inches southeast from there. The heaviest
amounts will be from roughly southeast of a Sioux City to Spencer
line where 3 to 7 inches are possible.

Winds: By Saturday night the combination of stout cold advection and
a tight pressure gradient will lead to gusty
northerly/northwesterly winds thru the day Sunday. NAEFS guidance
continues to show 850 mb winds in the 97th percentile of
climatology or higher. With forecast soundings showing winds of 35
to 45 kts sitting at the top of the mixed layer and varying
degrees of favorable low level lapse rates, expect blowing snow to
be a significant issue. Winds will gradually subside from west to
east late Sunday afternoon and evening.

Headlines: Will maintain the going Winter Weather Advisory over NW
IA this morning for any lingering patchy freezing drizzle and the
initial snow this afternoon. Will then transition to a Blizzard
Warning by early evening which was a good compromise of the heavier
snow and arrival of stronger winds. Expanded the Blizzard Warning
into the I-29 corridor starting at midnight given the additional
fluffy snowfall that occurred this evening and the general lack
of freezing drizzle to cap the existing snow cover. Also added an
Winter Weather Advisory west to around the James River where
blowing snow will also be a significant concern but confidence in
widespread blizzard conditions was lower.

.LONG TERM...(Sunday through Friday)
Issued at 358 AM CST Sat Feb 23 2019

Monday thru Saturday: With active weather in the near term, made
minimal changes to the extended portions of the forecast. With
fairly zonal flow aloft and the presence of occasional mid level
frontal forcing and/or quick moving shortwaves, will continue to
see occasional light snow chances through the week. Temperatures
will also remain well below normal with high temperatures Monday
struggling to make it out of the single digits in many locations.
This may result in advisory level wind chills Monday morning.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 520 AM CST Sat Feb 23 2019

Multiple aviation concerns over this TAF period. To begin with,
the feared FZDZ seems to have largely manifested itself as some
fog and occasional flurries this morning with a decreasing trend
by mid morning or so. Attention then turns to the incoming strong
winter storm that will largely impact locations south of our area
but will still clip areas of NW Iowa, including KSUX. Snow chances
will by on the increase by late afternoon into the evening,
highest at KSUX but some light snow is also possible at KFSD.
After snow moves out late this evening, strong northwesterly winds
will strengthen and likely lead to significant blowing snow,
especially for locations along and east of the I-29 corridor.
Blizzard conditions are possible at both KFSD and KSUX with the
lowest visibilities expected at airfield in exposed open areas.


SD...Winter Weather Advisory until 6 PM CST this evening for SDZ071.

     Winter Weather Advisory from midnight tonight to 6 PM CST Sunday
     for SDZ038-039-053-054-059>061-065-066-068>070.

     Blizzard Warning from 6 PM this evening to 6 PM CST Sunday for

     Blizzard Warning from midnight tonight to 6 PM CST Sunday for

MN...Blizzard Warning from midnight tonight to 6 PM CST Sunday for

IA...Winter Weather Advisory until 6 PM CST this evening for IAZ003-

     Blizzard Warning from 6 PM this evening to 6 PM CST Sunday for

     Blizzard Warning from midnight tonight to 6 PM CST Sunday for

NE...Winter Weather Advisory until 6 PM CST this evening for NEZ014.

     Blizzard Warning from 6 PM this evening to 6 PM CST Sunday for

     Winter Weather Advisory until 6 PM CST Sunday for NEZ013.



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