Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 201758

Area Forecast Discussion
National Weather Service Sioux Falls SD
1158 AM CST Fri Jan 20 2017

.SHORT TERM...(Today and Tonight)
Issued at 314 AM CST Fri Jan 20 2017

Drizzle/fog will be the primary focus through today, with some areas
of light rain or a little light snow developing tonight.

For today, lowest early morning visibility per surface observations
and webcam imagery located east of the James River Valley, as well
as farther west toward higher elevations of central South Dakota.
HRRR/RAP visibility progs suggest this will remain the case through
mid morning, with visibility gradually improving for most areas by
the end of existing of advisory. Exception could be in the highest
elevations of southwest Minnesota, where some models suggest 1/4SM
visibility could persist through much of the day. Will stick with
existing end time of advisory for now, but day shift will want to
closely monitor for possible extension in these higher elevations.

As for drizzle, has been periodic since yesterday afternoon, and
expect this trend to continue, primarily where low level moisture is
the deepest. This again looks to be in areas east of the James River
Valley through much of the day, but models show decent agreement in
expanding the deeper moisture westward into the James Valley through
the late afternoon/evening. Will expand drizzle mention accordingly.
Temperatures today will really move little from current readings,
with highs from the mid 30s in southwest MN to lower 40s through the
Missouri River Valley.

For tonight, models showing an increase in mid level moisture as an
upper level trough swings northeast across the area. This should
provide for introduction of ice into the persistent stratus deck,
allowing for more of a bonafide light rain vs. just drizzle. Some
light rainfall amounts of 0.10" to maybe 0.20", mainly in northwest
Iowa/southwest Minnesota. Soundings generally look warm enough for
just a cold rain, but the surface-based warm layer could become
shallow enough during the latter half of the night for some mixing
with wet snowflakes. This appears most likely north of Sioux Falls
and especially in the higher elevations of southwest Minnesota where
some very light snow accumulations could occur. With the continued
southerly flow and deep moisture along/east of the James Valley
through most of the night, temperatures should remain on the mild
side and have favored a blend of raw model solutions over the cooler
influence of MOS guidance.

.LONG TERM...(Saturday through Thursday)
Issued at 314 AM CST Fri Jan 20 2017

On Saturday the shortwave lifts off into the Upper Mississippi
Valley, with any light rain and snow for the most part diminishing
from west to east during the day. Cold air advection is pretty weak
behind the wave, so it will be another fairly mild day with highs
mid 30s to lower 40s. Cannot rule out some lingering flurries/very
light snow through east central SD/southwestern MN even into Sunday
as the aforementioned shortwave only slowly spins away, but any
accumulation would be negligible. There still looks to be
considerable cloud cover across the region for Saturday night and
Sunday, and temperatures will remain above normal with lows in the
20s and highs mid/upper 30s.

Not many changes on Monday, although it should be dry. May see a
little more sun that day with highs again 30s to near 40.

Still looking at a decent system affecting the region late Monday
night into Wednesday as an upper level low lifts out of the
southern/central Rockies and into the Central Plains during that
time frame. Models are in fairly decent agreement on the track of
the system, with slight timing differences, but still looking at
decent precipitation amounts across the area centered on Tuesday
into Tuesday evening. There is not any real cold air associated with
the system, though temperatures aloft will be cold enough to
preclude any freezing rain or sleet. In light of that, precipitation
type comes down to rain or snow dependent on surface temperatures.
At this time, surface thermal profiles suggest that most areas would
receive snow, with the better chances of rain mixing in confined to
the lower MO River Valley where highs on Tuesday may get into the
upper 30s. Light snow will then linger into Wednesday, and slightly
cooler air will filter in behind the system, though readings will
still be above normal with highs upper 20s to lower 30s.

An upper level trough then settles into the central and eastern
CONUS for the end of next week. This will bring temperatures a
little closer to normal, with only minimal chances of precipitation
for the period.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1148 AM CST Fri Jan 20 2017

IFR/LIFR conditions ceilings and visibility will continue through
the TAF period, mainly east of the James River. There will be a
slight improvement late this afternoon, but ceilings/visibility
could drop to 1 mile or less late tonight due to a short wave
lifting northeast producing drizzle/light rain across the TAFs
sites. The light precipitation may saturate the near surface
later, resulting in widespread fog once again late tonight.


SD...Dense Fog Advisory until 3 PM CST this afternoon for SDZ040-056.

MN...Dense Fog Advisory until 3 PM CST this afternoon for MNZ071-080-

IA...Dense Fog Advisory until 3 PM CST this afternoon for IAZ001>003-



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