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fxus63 koax 240953 
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Area forecast discussion
National Weather Service Omaha/valley NE
353 am CST Sat Feb 24 2018

Short term...(today through monday)
issued at 349 am CST Sat Feb 24 2018

Wintry precipitation today is the primary forecast concern, with
warmer temperatures arriving just in time for the start of the work
week.

A complex scenario is beginning to play out this morning. First,
open mid level wave was beginning to emerge from the central rockies
with a broad baroclinic Leaf pattern spreading across western and
north central Nebraska and into South Dakota as shown on infrared
satellite loops. Saturation of mid levels there was introducing ice
nuclei to produce snow as primary precipitation type. This area
is expected to spread northeast across northeast Nebraska through
the day, producing snow through the event. Farther southeast,
drier mid levels will inhibit seeder-feeder mechanism as lower
levels become increasingly more saturated through the morning.
Temperature profiles support mainly super-cooled liquid droplets
from Interstate 80 and south through the morning before some
moistening and cooling toward -10c at 700mb becomes likely. Thus
expect mainly freezing drizzle or freezing rain in the southeast
half of our County Warning Area much of the morning before some mix with or change
to snow occurs. And in the far southeast sections of southeast
Nebraska and southwest Iowa, temperatures close to 30 now will
likely inch above freezing by late morning, limiting icing
potential there after noon.

Also of note, diffluent mid level flow ahead of approaching
shortwave was inducing strong insentropic upglide over cool surface
air. We were already seeing areas of freezing rain as of 3 am in
southeast Nebraska, and that was spreading north toward the Omaha
Metro area. Radar returns suggested small convective elements
within this larger area of rain/drizzle, so there will likely be
some sleet mixed in with the broader area of freezing
precipitation.

With all that said, we will certainly continue our Winter Weather
Advisory across all of eastern Nebraska and southwest Iowa. Up to 3
inches of snow is likely in northeast Nebraska, with a mix of icing
totaling over a tenth of an inch followed by up to an inch of snow
along and a County or two either side of Interstate 80. Icing will
be the primary threat in far southeast Nebraska and far southwest
Iowa where forecast soundings keep mid levels dry the longest and
temperature profiles warmer than -10c. Could see a tenth of an inch
of ice there this morning, but with temperatures expected to rise
above freezing this afternoon, the impacts should decrease after mid
day.

Precipitation will be swinging through eastern Nebraska this
afternoon, and will be well east of southwest Iowa early this
evening. Subsidence behind exiting wave and low level westerly
flow should help to clear skies overnight. Colder airmass will
settle over the region tonight, but no where close to the Arctic
and Canadian air masses we've seen the last several weeks. 850
temps only drop into the -2c to -4c range. Still with clear skies,
light winds and some new snow/ice cover, expect temps to drop
into the teens most areas by Sunday morning.

A weak mid level shortwave is forecast to progress through the
region on Sunday, but with lack of significant moisture and lift,
don't expect precipitation. However variable cloud cover will limit
warming somewhat, and cool 850 temps remain in place. So despite a
favorable southwest low level wind component, expect highs in the
30s for most of the area, with lower 40s in southeast Nebraska and
southwest Iowa.

Monday is another story as mid level heights begin to rise in the
wake of exiting Sunday shortwave and ahead of deepening trough in
the west. Increased south to southwest low level flow is also
expected as a result of strong shortwave moving across the Canadian
border. 850 temps gain about 5c by Monday afternoon under plenty of
sunshine. Model output has been persistent in showing 50s for the
southern half of our County Warning Area and 40s in the north, and see no reason to
doubt that now.

Long term...(monday night through friday)
issued at 349 am CST Sat Feb 24 2018

Temperatures are expected to average closer to normal for the
remainder of the week, with a chance for precipitation coming
Wednesday into Thursday. Overall mid level flow pattern will
initially feature a trough in the west for Tuesday with southwest
flow aloft across the plains. A cold front trailing the strong
shortwave moving along the Canadian border Monday will slide into
our region on Tuesday. Timing of this front has slowed with the
latest model runs, suggesting our southern County Warning Area will stay on the
warmer side of the boundary on Tuesday. A 30 degree spread in high
temperatures from northeast Nebraska into southwest Iowa and
southeast Nebraska could occur then, with 30s highs in the north and
60s in the south. We slip to the colder side of the front for
Wednesday and Thursday when the western trough ejects into the
plains as an open wave. Temperature profiles then suggest a variety
of precipitation types are possible, but would favor snow in our
north and rain in our south initially on Wednesday before changing
to all snow Wednesday night. Still a way out for this one, but with
the speed of the system, not looking at a major event.

&&

Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1127 PM CST Fri Feb 23 2018

Moist, northeast low-level flow has resulted in IFR to LIFR
ceilings and lowering visibilities at the taf locations as of 05z.
These conditions will persist with light precipitation gradually
overspreading the region through 12z Saturday. It still appears
that precipitation type will remain predominantly snow at kofk,
while a mixture of snow, freezing rain or drizzle, and perhaps
some sleet appear possible at koma and klnk. A transition to all
snow appears probable at koma and klnk by early to mid afternoon
with precipitation ending at all taf sites by early Saturday
evening.



&&

Oax watches/warnings/advisories...
NE...Winter Weather Advisory until 6 PM CST this evening for nez011-
012-015>018-030>034-042>045-050>053-065>068-078-088>093.

Iowa...Winter Weather Advisory until 6 PM CST this evening for iaz043-
055-056-069-079-080-090-091.

&&

$$

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