Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 131708
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1108 AM CST Fri Jan 13 2017

.SHORT TERM...(Today and Tonight)
Issued at 322 AM CST Fri Jan 13 2017

Narrow shortwave just beginning to enter the Western Dakotas this
morning. A very narrow band of light snow has developed over south
central South Dakota and northern Nebraska. This band of snow is
expected to pivot eastward across the CWA today.  The wave will
begin to run into drier air and also shows signs of shearing out by
mid-day. Nevertheless, a quick half inch of snow could be possible
as it moves through.  Reaching the Sioux Falls area around daybreak
and Marshall/Worthington area after 9am.  Snow is expected to move
east early this afternoon.

The increasing cloud cover associated with this wave is allowing
temperatures to rise in many areas. Temperatures are still either
side of -10 along the Buffalo Ridge, but the variable nature of the
winds is keeping wind chill values rather sporadic around the -20
range. If trends continue, may be canceling wind chill advisory
early.

Winds will remain light and variable into Saturday morning. Once
again allowing temperatures to fall below zero in many areas. With
winds trending lower, wind chills shouldn`t pose a risk into
Saturday morning.

.LONG TERM...(Saturday through Thursday)
Issued at 322 AM CST Fri Jan 13 2017

We are looking at moderating temperatures for Saturday and Sunday in
a westerly upper level flow as surface high pressure slides slowly
eastward across the region. Highs on Saturday will climb into the
20s, approaching 30 through the Missouri River corridor. Even warmer
for Sunday as readings climb into the mid 20s to lower 30s. By
Sunday afternoon warm air advection aloft will increase over the
area as a upper level low begins to lift out of the lower Four
Corners region. With that, could see light precipitation develop
through the Vermillion to Storm Lake corridor. Still seeing model
differences with regard to thermal profiles and the extent of
warming aloft for that time frame, with the ECMWF continuing to
offer the warmest solution. In light of the differences kept a mix
of freezing rain and snow over that area for Sunday afternoon,
though anything that occurs would be very light.

On Sunday night and Monday the aforementioned upper level low lifts
into the Central Plains with increasing precipitation chances over
our area. As has been the trend of late, the ECMWF continues to take
a farther westward track with the low than the GFS/GEM. As a result,
it pulls warmer air back to the west over our area, which would
result in a much more extensive area of freezing rain over our CWA
than the other two models. It is still a little too far out to
ascertain exact precipitation types at this point, but all models
are bringing plus 0 C air aloft into at least our southeast by
Monday morning, portending mostly freezing rain over that area. The
question then becomes how far west the freezing rain will extend
before cooler air begins to filter in behind the system on Monday
afternoon, allowing precipitation to transition to snow. Based on
current model trends it increasingly appears that freezing rain is
going to be the bigger player in this event, with any snow being
rather insignificant. With highest confidence in precipitation type
for our southeast, went ahead and expanded the Winter Storm Watch
through most of northwestern IA and into extreme southeastern SD for
Sunday afternoon into Monday night. Current QPF and ice accumulation
grids only go until 00Z on Monday, and up to that time it looks that
a tenth to a quarter of an inch of ice may be possible through
northeastern NE and northwestern IA. Again, there could also be more
ice accumulation than currently forecasted back to the north and
west of this area, but confidence is lower.

The main story for the remainder of the long term is a warming trend
through the period in a west/southwesterly upper level flow.
Temperatures will be above normal through the remainder of the week,
with highs climbing into the mid 30s to lower 40s by the end of the
week. Precipitation chances look to be minimal through the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1102 AM CST Fri Jan 13 2017

VFR conditions will prevail through the TAF period. SREF model
shows low visibility/ceilings due to fog around KHON site late
tonight . At this point, confidence is low; therefore decided not
to mention it in the TAFs.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from Sunday afternoon through Monday evening
     for SDZ070-071.

MN...None.
IA...Winter Storm Watch from Sunday afternoon through Monday evening
     for IAZ001>003-012>014-020>022-031-032.

NE...Winter Storm Watch from Sunday afternoon through Monday evening
     for NEZ013-014.

&&

$$

SHORT TERM...Dux
LONG TERM...JM
AVIATION.../05



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