Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 231122
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
522 AM CST Fri Feb 23 2018

.SHORT TERM...(Today through Sunday)
Issued at 345 AM CST Fri Feb 23 2018

Another wintry mix of precipitation on Saturday is the primary
forecast concern.

Low pressure system that brought our latest wintry mix of snow,
freezing drizzle/rain and sleet on Thursday was pushing toward the
Great Lakes region this morning. Behind it, cooler high pressure
will be settling into the Northern Plains and nosing toward the Mid
Missouri River Valley region today before sliding east tonight with
approach of next weather system swinging through the Rockies. Thus
cold air will not stay around long, with GFS showing 850 0C isotherm
remaining in or near southeast Nebraska and southwest Iowa through
tonight.

As Rockies system rotates into the Plains later tonight and
Saturday, low level warm advection will push that above 0C 850 air
north toward Interstate 80 by Saturday morning. Forecast soundings
show this warmer air riding over colder boundary layer air, with
diffluent flow ahead of Rockies wave inducing isentropic upglide
resulting in areas of precipitation breaking out in our southern CWA
late Friday night and Saturday morning. Forecast soundings suggest
mid level dry air over this region, thus no ice introduction into
lower moist layer, resulting in freezing drizzle/rain before
surface temperatures push above freezing later in the day, and
that appears to only affect far southeast Nebraska and southwest
Iowa.

Farther northwest, modest frontogenetical forcing is shown on cross-
sections, and forecast soundings indicate moistening of mid and
lower atmposphere will be complete by 12Z Saturday. Thus seeder-
feeder processes should produce mainly snow across northeast
Nebraska. Models have been lowering storm total QPF the last
couple of runs, but specific humidity calculations for a 12-hour
event still suggest close to 6 inches of snow is likely in parts
of northeast Nebraska.

As far as icing potential goes in the area a couple of counties
either side of Interstate 80, up to 0.15" is expected during the day
Saturday, with a likely mix with snow coming Saturday afternoon
totaling an inch or two.

Have gone ahead and issued Winter Weather Advisories for much of our
CWA where confidence is fairly high on some accumulations of both
ice and snow late tonight through most of Saturday. Left a few
counties in northeast Nebraska under a Winter Storm Watch where
totals could exceed 6 inches. And left out a few counties in our
far southeast where warm surface air intrusion early in the day
Saturday may limit icing.

After precipitation ends Saturday afternoon or evening, clearing
skies will allow temperatures to drop into the teens by Sunday
morning. However sunshine and westerly low level winds should help
temps rebound into the 30s over most of the area Sunday afternoon,
with some lower 40s in the south.

.LONG TERM...(Sunday night through Thursday)
Issued at 345 AM CST Fri Feb 23 2018

Closer-to-normal temperatures are expected much of next week as mid
level flow favors a west to southwest direction. Monday could be
really mild as southwest low level flow is realized owing to a
strong shortwave moving through the Northern Plains. Colder air
settles south behind that wave for the rest of the period into
Thursday, keeping surface temperatures a bit cooler than mid level
flow would suggest. While models begin to diverge at mid week, a
blended consensus of model output shows a shortwave ejecting from
the southwest into the Plains on Wednesday, bringing another shot of
precipitation. GFS would again indicate a mix of precipitation types
across our area, while ECMWF is a bit warmer and would suggest
mainly a liquid event.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 518 AM CST Fri Feb 23 2018

A batch of IFR/LIFR cigs in north central Nebraska will work
southeast through early afternoon, reaching KOFK early in the TAF
period. By late morning, those cigs will lift to MVFR as they
approach KOMA and KLNK, with a gradual scattering of cigs during
the afternoon. MVFR cigs will again spread across eastern Nebraska
by 06Z as a storm system moves toward the area. Some freezing
drizzle or light snow could affect TAF sites between 06Z and 12Z,
but was not mentioned in this cycle as timing is in question.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from 3 AM to 6 PM CST Saturday for
     NEZ015-030>034-042>045-050>053-065>068-078-088>090.

     Winter Storm Watch from late tonight through Saturday afternoon
     for NEZ011-012-016>018.

IA...Winter Weather Advisory from 3 AM to 6 PM CST Saturday for
     IAZ043-055-056-069-079.

&&

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...Dergan


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