Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 140525

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1125 PM CST Fri Jan 13 2017

.SHORT TERM...(Tonight through Sunday)
Issued at 312 PM CST Fri Jan 13 2017

...The primary concern remains the winter storm which will impact
the forecast area Sunday into Monday night...

Manual 12z upper-air analysis and early afternoon water vapor
imagery indicate a mid to upper-level cyclone off the southern CA
coast with a downstream zone of confluent mid-level flow observed
from the upper MS Valley into the Great Lakes. The confluent flow
aloft was maintaining the presence of an anticyclone at the
surface over MN/WI with the primary low-level baroclinic zone
situated from southwest TX through the lower MS Valley as of 18z.
Of note in 12z observed sounding data was a seasonably moist low-
level air mass which extended from south TX into southwest MO.

In the near term, there is little in the way of sensible weather
concerns. The confluent mid-level flow to our northeast will
maintain a surface ridge across the mid MO Valley, which coupled
with persistent clouds, will support near or slightly below normal
temperatures through Saturday.

Saturday night into Sunday, the mid to upper-level low mentioned
above will turn east across northwest Mexico, which will induce
strengthening southerly low-level winds. This, in turn, will
enhance the poleward flux of the warmer, more moist air mass to
our south. This moistening process in conjunction with a
broadening zone of warm advection will foster an expanding
precipitation shield from south to north across the forecast area.
Initial precipitation type will likely be a sleet-freezing rain
mix which will transition to freezing rain as the warm advection
continues atop the shallow, sub-freezing air mass.

.LONG TERM...(Sunday night through Thursday)
Issued at 312 PM CST Fri Jan 13 2017

Sunday night into Monday, we continue to see considerable spread
amongst deterministic and ensemble model data in the track of the
upper-air system through the central Plains into the mid and
lower MO Valley. These differences have implications on the
surface pattern, the stratification of the thermal profiles and
resultant precipitation type. The ECMWF remains the warmest and
farthest west solution, while the GFS is the coolest and farthest
east, with a considerable departure noted from the previous (06z)
forecast. As a result of this model variability, confidence in
specific ice and snowfall accumulations remains lower than we
would like at this juncture. The official forecast will indicate
the swath of highest ice accumulations from near Fairbury, NE
(0.50") into southwest IA (0.30-0.35"), with 0.30-0.40" possible
along the I-80 corridor. The highest snowfall totals (i.e. 2-3")
are expected to occur over northeast NE, mainly along and to the
north of an Albion-Norfolk-Wayne line.

We would like to stress that these snow and ice accumulations are
likely to change between now and the onset of the weather event,
as the models eventually come into better agreement. Due to the
uncertainties mentioned above, we have elected to maintain the
Winter Storm Watch, instead upgrade to a warning. A warning
upgrade to some or all of the watch area is quite likely in the
next 24 hours, once confidence in the weather scenario increases.

Monday night into Tuesday morning, we will see a transition from
rain or freezing rain to light snow as the cold air deepens on
the backside of the departing cyclone. Snow amounts during that
time frame should be relatively light.

By the middle to latter part of next week, it appears that
developing zonal flow aloft will induce downslope warming with
afternoon temperatures rising into the 40s. Much of the
precipitation that falls on Sunday and Monday will be runoff into
area streams. This added volume coupled with ice melt from the
warming temperatures could present some ice jam issues later next


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1125 PM CST Fri Jan 13 2017

MVFR ceilings over southeast NE and southwest IA have not eroded
at all the past 6 hours. These should hold on at least a few more
hours before winds become west/northwest in the cloud layer to
force them farther to the southeast. Then look for VFR conditions
during the day Saturday into Saturday evening with winds less than
10 knots.


NE...Winter Storm Watch from Sunday afternoon through late Monday
     night for NEZ011-012-015>018-030>034-042>045-050>053-

     Winter Storm Watch from Sunday morning through late Monday night
     for NEZ078-088>093.

IA...Winter Storm Watch from Sunday afternoon through late Monday
     night for IAZ043-055-056-069-079-080-090-091.



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