Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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074
FXUS63 KOAX 150526
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1126 PM CST Sat Jan 14 2017

.UPDATE...
Issued at 1002 PM CST Sat Jan 14 2017

Left exit region of the upper level jet and lift saturating the
mid layers enough to produce some patchy sleet and freezing rain
across southeast Nebraska this evening. Steadier precipitation
is across southern Kansas and Oklahoma. NAM and an early look at
the GFS along with the ESRL HRRR/RAP13 trend toward increasing
freezing rain coverage across southeast Nebraska between 09-12Z.
Subjective surface analysis has mid 20s dewpoints over central
Kansas and obs have some patchy lower cigs near Concordia and
Manhattan, KS. Enhanced IR imagery in southwest Kansas related to
the strengthening low level jet slowly moving northward and
increasing mid level lift. Deeper moister will approach southeast
Nebraska/isentropic upglide overnight. Made some changes to the
ice storm headline to start it a few hours earlier near the Kansas
border and to include Seward/Lancaster/Cass counties in with the
earlier group vs. waiting until noon due to the HRRR/RAP trends.

&&

.SHORT TERM...(Tonight through Tuesday)
Issued at 235 PM CST Sat Jan 14 2017

...The primary forecast concern is the winter storm that will
impact the area Sunday into Monday night...

Water vapor imagery as of midday indicates a mid to upper-level
low beginning to assume more of an eastward movement near the tip
of the Baja spur. Latest model guidance has started to converge on
a more consistent track of this system, with it`s location
expected to be over western TX/eastern NM at 00z/Mon and near the
junction of the NE-KS-MO borders by 00z/Tue.

In the low levels, a surface high presently over the mid MO
Valley will shift east tonight into Sunday in deference to a
deepening lee cyclone over the southern High Plains. This low will
develop northeast into northwest MO by 00z/Tue, in tandem with the
parent upper-air system. Strengthening southerly low-level winds
ahead of the migratory cyclone will advect a seasonably moist air
mass present over the southern Plains this morning north into the
region, atop a shallow, sub-freeing air mass.

Intensifying low-level warm advection and isentropic upglide will
foster the northward expansion of a warm-conveyor precipitation
shield through the central Plains tonight with this activity
moving into southeast NE toward sunrise Sunday. Forecast
soundings indicate that the predominant precipitation type will
be freezing rain, possibly mixed initially with some sleet. The
precipitation shield will subsequently spread north across the
remainder of eastern NE and southwest IA Sunday into Sunday night
ahead of the approaching deep-layer cyclone.

The highest precipitation rates are expected to materialize across
the forecast area on Monday in concert with the arrival of the
strongest deep-layer forcing for ascent. A change over from
freezing rain to rain is forecast to occur Monday morning over
southeast NE and far southwest IA as the persistent warm
advection pushes surface temperatures to above freezing. Current
indications are that this trend will continue north into east-
central NE (including the Omaha metro) by Monday afternoon, while
over our far northwest counties a snow band will become better
organized within the increasingly baroclinic deformation axis.

It still appears that the axis of greatest ice accumulation will
stretch from near Fairbury and Beatrice through east-central NE
into southwest IA where amounts will range from around a half inch
on the western end to about 0.35" from Omaha eastward. Highest
snowfall amounts are expected over our far northwest counties
where three to four inches are possible. Given the growing model
consensus with the track of this weather system, enough
confidence exists for an upgrade to an ice storm warning from
Sunday through much of Monday night for all but our northwest
counties. There, the combination of accumulating ice and snow
warrants a winter storm warning, which will go into effect Sunday
night and similarly continue through most of Monday night.

.LONG TERM...(Tuesday night through Saturday)
Issued at 235 PM CST Sat Jan 14 2017

A phase change from rain or freezing rain to light snow will occur
Monday night along the trailing deformation precipitation band as
it advances east/southeast across the area. By this time, the
stronger forcing for ascent and higher moisture content will have
shifted to the east/northeast of the region, so snowfall amounts
should remain light.

By the middle of the upcoming week, building heights aloft and
enhanced downslope flow in the low levels will yield considerably
warmer temperatures with afternoon highs rising into the 40s. Runoff
from the Sunday-Monday system coupled with ice melt associated with
these warmer temperatures could result a rise in area streams and
perhaps some ice jam activity.

By next Friday into the weekend, model spread increases with
regard to the evolution of the next major trough over the western
CONUS. Regardless of the model differences, it does look like
precipitation chances will increase during that time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1130 PM CST Sat Jan 14 2017

Overall, look for decreasing cloud bases overnight and into
Sunday. The main precipitation should hold off until the
afternoon Sunday, but KLNK could see some freezing rain in the
morning. IFR conditions possible at KLNK by late afternoon and
IFR conditions possible at KOMA by Sunday evening.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Ice Storm Warning from noon Sunday to 3 AM CST Tuesday for
     NEZ015-032>034-042>045-050>053-067.

     Ice Storm Warning from 3 AM Sunday to 3 AM CST Tuesday for
     NEZ065-066-068-078-088>093.

     Winter Storm Warning from 6 PM Sunday to 3 AM CST Tuesday for
     NEZ011-012-016>018-030-031.

IA...Ice Storm Warning from noon Sunday to 3 AM CST Tuesday for
     IAZ043-055-056-069-079-080-090-091.

&&

$$

UPDATE...Zapotocny
SHORT TERM...Mead
LONG TERM...Mead
AVIATION...Miller



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