Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 120023

Area Forecast Discussion
National Weather Service Omaha/Valley NE
623 PM CST Wed Jan 11 2017

.SHORT TERM...(tonight through Saturday)
Issued at 406 PM CST Wed Jan 11 2017

A relatively cold period the next few days with a couple chances for
wintry precip.

Cold air slammed into the region this morning behind another arctic
cold front. Temperatures plunged from the 30s this morning into the
teens and 20s on north winds gusting over 30 mph at times. The
colder and dendritic temperatures and a little low level instability
produced a few flurries this afternoon as well.

A large and broad mid level low/trough sprawling across Canada and
the northern tier of the CONUS was responsible for the cold air
plunge. Flow over us was more zonal or slightly southwesterly this
afternoon, with a ripple of energy noted entering northwest
Nebraska. That ripple is forecast to slide across SD/NE border
area tonight, triggering an area of snow across northern Nebraska
into northern Iowa. Certainly cold enough for all snow with this
system, but progressive movement and limited moisture suggest
little more than a dusting of snow is expected in most of the
area, with upwards of an inch or so in far northeast Nebraska.

That system will be moving off to the east early Thursday, leaving
cold temperatures in its wake, some 10 degrees below normal. Then a
similar ripple is expected to ride along a similar path late
Thursday night into Friday morning, with another dusting of snow
possible in our north. Again cold temps will be reinforced on back
side of this ripple for Friday afternoon when highs struggle into
the 20s.

Pattern begins to shift later Friday night into Saturday as upper
low diving down the West Coast pumps up heights in the Southern
Plains, and also spreads some moisture northward through OK/KS
toward southeast Nebraska and southwest Iowa. Meanwhile cold air
remains in place at the surface. The warmer and more moist air
riding over the colder surface air suggests at least a small chance
for freezing rain in our far southeast between midnight and sunrise
Saturday. Most of this precipitation should remain to our south as
model QPF is limited in southeast Nebraska and southwest Iowa, so
for now am not painting any icing there. A rebound in temperatures
toward 30 will follow for Saturday.

.LONG TERM...(Saturday night through Wednesday)
Issued at 406 PM CST Wed Jan 11 2017

The potential for a wintry mix of precipitation beginning Saturday
night and continuing through Monday night is the main weather story
for the longer term period.

Upper low diving down the West Coast early in the weekend is
expected to eject into the Plains Sunday and Monday. Plenty of Gulf
moisture will spread north ahead of it, with precipitation potential
beginning Saturday night in our south, and spreading across all of
eastern Nebraska and southwest Iowa during the day Sunday and early
Sunday evening. Temperature profiles show a warm layer aloft across
the southern half of eastern Nebraska and western Iowa, with
magnitude and depth of colder surface-based layer determining precip
type here. And there is some discrepancy between longer-range output
on what surface temps will be, as GFS is a little warmer than ECMWF.
Still both are hinting that temps will be at or below freezing for a
good part of Sunday and Sunday night when the bulk of the
precipitation is forecast to fall. Liquid amounts of an inch or more
are possible, so the potential exists for severe icing if
temperature profiles hold as models show. However there are some
indications above-freezing air will spread into southeast Nebrsaka
and southwest Iowa. Farther north, say from I-80 and north, more of
a mixed bag of precip seems more likely right now, with
sleet/snow/freezing rain all possible. Deeper cold air that would
change everything over to snow doesn`t arrive until most of the
precipitation moves off Monday night into Tuesday.

So for now, forecast package is based on a blend of GFS and ECMWF as
far as temperature profiles are concerned, which lead to a
plethora of precipitation types. Suffice it to say, we`ll have to
wait a little longer for this system to show its hand as any
slight wiggle in path or timing could lead to big differences in
precipitation types and thus impacts Sunday and Monday.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 544 PM CST Wed Jan 11 2017

88d mosaic was showing area of -SN currently over wrn/cntrl Neb
expanding NEWD...and beginning to spread into NE Neb. Given
trajectory trends over the last several...expect only KOFK will any
-SN activity/MVFR conditions during the evening hours.
Otherwise...VFR conditions will prevail the rest of the fcst pd.




LONG TERM...Dergan
AVIATION...DEE is the U.S. government's official web portal to all federal, state and local government web resources and services.