Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 130953
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
353 AM CST Fri Jan 13 2017

.SHORT TERM...(today through Sunday)
Issued at 352 AM CST Fri Jan 13 2017

00Z upper air analysis indicated 140-150 kt H25 jet from NEb into
the Great Lakes with the right rear entrance region over northern
NEb/southern SD early tonight. This along with a weak shortwave
trough was leading to a bit of -sn over northern NEb. This band is
expected to continue to slide east while weakening this morning.
We will continue to include some light snow in the forecast for
areas along highway 20 for a couple hours into the morning.

Otherwise the main story for the forecast is the potential winter
storm for late in the weekend. As expected at this range there are
some significant differences in the deterministic guidance to the
track of the upper-level cyclone and in the thermal fields. Given
these differences there is currently a below average confidence
to the sensible weather. We have removed any mention of
precipitation from tonight through Saturday evening for all of the
CWA. The 1046 mb arctic high sliding across the northern Plains
over the next 24 hours should provide ample dry air keeping any
precipitation south of our CWA. The timing of precipitation on
Sunday is in question as well. DProg/dt from various models
indicates the ejection of the upper-level cyclone is slower with
each successive run, and we will still have a good deal of dry
air around. Nevertheless models are generally consistant that a
slow saturation process will take place through the day as
insentropic ascent increases over the retreating southern Plains
boundary. Precipitation type is tricky from the start. With a top-
down saturation introducing ice into the column, and the thermal
profile all below 0C we may start with a bit of flurries or a
period of light snow on Sunday morning as activity lifts slowly
north, but this should become sleet and eventually freezing rain
in the south by afternoon.

.LONG TERM...(Sunday night through Thursday)
Issued at 352 AM CST Fri Jan 13 2017

The main event of the system appears to take place in the first
few periods of the extended forecast. Again the track of the upper
level cyclone and associated thermal profiles are very much in
doubt currently with the EC farthest northwest, slowest, warmest,
while the GFS is a compromise between the EC and the farther
southeast GEM. The main slug of forcing and associated batch of
precipitation is likely to head at the CWA late on Sunday night
and Monday morning. As the arctic high retreats to the east during
this period we will see a slow warming of the boundary layer
through the period. This is likely to change the freezing rain
over to rain in southeast NEb/southwest IA by Monday morning, and
up to the I80 corridor by mid to late moring on Monday. The
precipitation should decrease by afternoon as the mid-level dry
slot works overhead. We may see some regeneration of the
precipitation sometime Monday night depending on the track of the
upper-level cyclone and associated pocket of weak static
stability and renewed frontogenesis, but placement of this
additional band is very uncertain.

The main changes to the forecast were to decrease ice amounts for
most of the CWA. We will still have a quarter to as much as a half
inch in the southwest CWA decreasing to around a tenth to two
tenths for OMA and lessor amounts north. For the areas along the
Platte river and just north we increased the sleet though with .2
to .6 in forecasted. In the north the soundings support mainly a
sleet and snow mention with amounts of snow of 2-4 inches in the
far northwest and a tenth of two of sleet most areas. Also we
pushed back the start time of the watch to Sunday morning in the
south and Sunday afternoon in the central and northern CWA, and
closer to 00Z Monday may be more realistic in the northern CWA.
One bright spot from the event is that areas of southwest IA and a
good part of southeast NEb will see good warming during the day on
Monday, which should significantly help with travel.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1105 PM CST Thu Jan 12 2017

VFR conditions expected thru the fcst pd.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Storm Watch from Sunday afternoon through late Monday
     night for NEZ011-012-015>018-030>034-042>045-050>053-
     065>068.

     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.

&&

$$

SHORT TERM...
LONG TERM...
AVIATION...DEE



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