Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 222125

Area Forecast Discussion
National Weather Service Sioux Falls SD
325 PM CST Thu Feb 22 2018

.SHORT TERM...(This evening through Friday)
Issued at 302 PM CST Thu Feb 22 2018

Warm air advection regime ahead of a trough digging across the
southern Rockies this evening will continue to bring precipitation
to the area. With a well pronounced jet streak lifting across the
forecast area, as well as the shortwave lifting northeastward
into the Mid-Missouri Valley overnight, expect widespread snowfall
to continue lifting out of Nebraska, impacting the area this
evening. There remains a freezing rain threat in our southeast.
Snow will taper off from west to east, finally exiting to the
northeast not long after midnight.

For the late afternoon and early evening, mid level saturation will
remain a problem across areas mainly east of I-29 and south of I-90
with a pocket of drier air in the mid levels. With the lack of
moisture in the snow growth zone, light freezing rain or drizzle will
remain a concern here through the evening, potentially mixing
with or changing over to snow. Elsewhere, much better saturation
is expected, allowing precipitation to primarily fall as snow,
however there may briefly be light freezing drizzle mixing with
snow in far southeast SD at onset. Snowfall amounts and icing
amounts (up to 0.10" in far northeast NE and northwest IA) remain
on track, therefore will leave the winter weather headlines for
this afternoon and evening as is.

Friday will be dry with relatively light northwest winds.
Temperatures will be a little below normal with highs in the mid to
upper 20s.

.LONG TERM...(Friday night through Thursday)
Issued at 302 PM CST Thu Feb 22 2018

All eyes will be on the next weather system, which has potential
to be an even larger impact than today`s system. Trough digs into
the Four Corners region Friday afternoon and deepens as it moves
northeast into Colorado. Surface low pressure likewise deepens
near the Oklahoma Panhandle by daybreak Saturday. As the low lifts
northeast across the central Plains, the trough becomes
negatively tilted, and very strong mid and upper level PV/dynamics
lift into the mid Missouri Valley, far southeast SD, northwest
IA, and southwest MN on Saturday afternoon through Saturday night.
Strong mid level frontogenesis also develops midday Saturday
across far southeast SD into northwest IA and southwest MN, with
indications of elevated instability developing above the
frontogenesis. This area will be the main focus of the heaviest
snowfall. The question will be exactly where this heavier snow
band will develop. The latest GFS has trending further west with
the band, backing it closer to the SD/IA and MN border. The NAM
remains far too progressive with the timing of the system, so will
discount for now. Did nudge QPF values 50 percent towards WPC
which ingested a little more of the GFS and ECMWF, to shift the
band slightly east. This also bolstered amounts slightly within
the most probable location for banding. Within this band cannot
rule out 8 or more inches of snow, with amounts tapering off
quickly to the west of the band.

It is likely that the entire forecast area will see some
accumulations, and confidence continues to rise that areas near and
east of I-29 will see significant snow. Of course, as with all
banded events, confidence remains fairly low as to exactly where
the heaviest amounts will fall. Given the increase in confidence
that significant snows will fall, will issue a winter storm watch
for Saturday and Saturday night. It is likely that as the storm
nears, snowfall amounts will shift and headlines will be adjusted,
but will highlight the areas with the greatest potential for 6
inches or more of snow. Fortunately, winds do not look
particularlystrong during the event, but northwest winds do
increase as it exits late Saturday into Sunday. Could see a very
small window where dry mid levels could bring the threat for
freezing drizzle or rain on Saturday morning, but right now it
doesn`t look like the icing will be a big concern.

Beyond Saturday`s system, did not adjust the going blended forecast.
The good news is that temperatures moderate into mid week.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1136 AM CST Thu Feb 22 2018

Aviation concerns center around snow and associated low ceilings
and visibility through late this evening. At 1730 UTC, snow was
along the Missouri River in SD and moving to the northeast. This
snow is expected to expand in coverage and spread into Huron and
Sioux Falls by mid afternoon. There will be a period of 1/2 to 1
mile visibility with snow in both locations from late this
afternoon through the mid to late evening before the snow moves to
the east. In addition, ceilings will be from 500 to 1000 feet
during most of the snowfall. Once the snow ends, visibilities will
rapidly rise above 6 miles but ceilings will remain IFR to MVFR
through late night before slowly clearing after 12Z Friday. In
KSUX, there will likely be periods of freezing drizzle through mid
afternoon before light snow spreads into the area. Visibilities
are expected to generally be above 1 mile although IFR to LIFR
ceilings are expected. Snow will end by 0400 UTC with ceilings
improving by 12Z.


SD...Winter Weather Advisory until midnight CST tonight for

     Winter Storm Watch from Saturday morning through Saturday
     evening for SDZ056-062-066>071.

MN...Winter Weather Advisory until midnight CST tonight for MNZ071-

     Winter Storm Watch from Saturday morning through Saturday
     evening for MNZ071-072-080-081-089-090-097-098.

IA...Winter Weather Advisory until midnight CST tonight for

     Winter Storm Watch from Saturday morning through Saturday
     evening for IAZ001>003-012>014-020>022-031-032.

NE...Winter Weather Advisory until midnight CST tonight for NEZ013-

     Winter Storm Watch from Saturday morning through Saturday
     evening for NEZ013-014.



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