Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 151838
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1238 PM CST Sun Jan 15 2017

.SHORT TERM...(Today and Tonight)
Issued at 414 AM CST Sun Jan 15 2017

Large scale picture early this morning shows compact closed low
across far northwest Mexico, with flow upstream transitioning toward
a confluent ridging across the Northern Plains. Any meaningful sky
cover has been diverted south of the area so far. Plenty of
convection noted ahead of the upper wave, and wonder what impact
this will have on track of system heading through tonight. Model
trends exhibited for nearly all solutions was a much slower
northward progression to the moisture and lift forcing this evening
and through the overnight. While clouds will certain begin to
encroach from the south during the day, not likely to see any
precipitation threat through the day, and temps will again claw
their way to above normal readings, especially south of I-90 where
lower 30s will be common. A generally light southerly flow expected
today, perhaps a bit stronger toward the Buffalo ridge where even
some near 30 degree readings will be possible.

Main focus for the immediate term comes with impending wintry system
tonight. Main upper low slowed, and will still be well to the south
across the southern Plains by 12z. Advections plenty meager thru 03z-
06z time frame, so have backed off on spread of precipitation this
evening.  Despite the initiation of some low freezing rain chances
from 03z-06z near Highway 20, the start of the Ice Storm Warning
has been backed off for three hours to 06z (with expected start to
more widespread ice accumulations probably a couple or three more
even later on north edge of the area). For those areas within the
Winter Storm Watch more certain to receive a lesser coating of
ice before receiving a couple or three inches of snowfall, the
watch has been transitioned to a Winter Weather Advisory,
including areas from around KMJQ through KSHL and east of KYKN.
The start time of the advisory will be 09z for extreme southeast
SD, northeast NE, and northwest IA, with after 12z north of the
Iowa border. With some uncertainty as to the potential for any
ice, have left a small area of winter storm watch in effect
including KMWM, KDVP, KLYV, KFSD and KYKN, again with the same
backing off on start time by 3-6 hours.

Temperatures aloft will ensure that even the wet bulb readings will
remain above zero. A fairly deep isothermal layer above zero will
develop, but temps likely no more than 2-3C, which leads precip type
procedure to lead to a more sleety solution. However, cold layer
near the surface is not expected to be very strong, and refreeze
potential is fairly weak especially through the Ice Storm Warning
area. Looks to be more of a freezing rain scenario, with chance for
a little sleet, but more threat for some snow on the far northern
edge of precip shield as more effective wet bulb exists.

.LONG TERM...(Monday through Saturday)
Issued at 414 AM CST Sun Jan 15 2017

The slower solutions of the most recent model runs will keep
precipitation primarily confined to areas south of Interstate 90
through 18Z on Monday. Another trend of recent model runs is to take
the system a little farther southeastward. This has resulted in
slightly cooler thermal profiles aloft and shunted the highest QPF a
bit to the east. The trends have not changed the forecast
considerably, though may result in a little more snow over our CWA
in terms of precipitation type. In any event, still looking at
significant icing over northwestern IA where warmer temperatures
aloft reside longer and QPF is highest. The current Ice Storm
Warning is still appropriate with a quarter to three tenths of an
inch of ice possible over that area through the period of late
tonight through Monday evening. For the remainder of the CWA.
thermal profiles support mixed precipitation south of Interstate 90
on Monday morning , with snow to the north of this area, then
transitioning to all snow from west to east through the day. Removed
sleet from the forecast as a weather type with bufkit soundings
suggesting sleet was unlikely. Models indicating heaviest QPF
between 18Z and 00Z when forcing is optimized as the upper level low
slides just to our southeast during that time frame. As was the case
yesterday, given Superblend QPF was too low for Monday afternoon, so
blended closer to WPC values for that period. By Monday evening most
precipitation should be in the form of snow as the system pushes off
to the east and thermal profiles continue to cool. Light snow will
then taper down by 06Z. As far as snow/ice totals for the event, at
this point ice accumulation will range from a possible light glaze
around Sioux Falls, to near a tenth of an inch through the
Vermillion to Canton to Worthington corridor, to a quarter inch or
more south and east of Sioux City to Spencer. The highest axis of
snowfall will reside just to the north and west of the highest ice,
with 2 to 3 inches of accumulation from the mid Missouri River
Valley into southwestern MN.

With short term concerns, there was little focus on the longer term
period. However, there is not much change from previous thoughts
with the extended outlook, as temperatures warm back to above normal
levels through the end of the week with highs in the 30s and 40s.
Precipitation chances look to be minimal, with the possibility of
light rain and snow toward the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1232 PM CST Sun Jan 15 2017

Aviation concerns will focus mainly on the incoming winter storm
on Sunday night. Ceilings expected to lower gradually into MVFR
range around KSUX toward 06z and IFR range after 09z. These low
ceilings will spread into areas mainly south of a Yankton to Sioux
Falls to Windom line through 18z. Along with the lowering
ceilings will come a light precipitation threat, which will
largely be in the form of light freezing rain or sleet. The
freezing precipitation will begin changing over to snow along the
western edge of the band late morning Monday, towards the end of
the TAF period. Winds remain light through the TAF period.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 3 AM Monday to midnight CST Monday
     night for SDZ070-071.

     Winter Storm Watch from late tonight through Monday evening for
     SDZ068-069.

     Winter Storm Watch from Monday morning through Monday evening
     for SDZ062-066-067.

MN...Winter Storm Watch from Monday morning through Monday evening
     for MNZ080-081-098.

     Winter Weather Advisory from 6 AM Monday to midnight CST Monday
     night for MNZ089-090.

IA...Winter Weather Advisory from 3 AM Monday to midnight CST Monday
     night for IAZ001>003-012-013-020.

     Ice Storm Warning from midnight tonight to midnight CST Monday
     night for IAZ014-021-022-031-032.

NE...Winter Weather Advisory from 3 AM Monday to midnight CST Monday
     night for NEZ013.

     Ice Storm Warning from midnight tonight to midnight CST Monday
     night for NEZ014.

&&

$$

SHORT TERM...Chapman
LONG TERM...JM
AVIATION...



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