Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 182345
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
545 PM CST Sun Feb 18 2018

.SHORT TERM...(Tonight through Wednesday)
Issued at 345 PM CST Sun Feb 18 2018

Forecast concerns continue to be the winds this afternoon, then
drizzle and freezing drizzle developing late tonight and
continuing Monday morning with a mix of sleet and snow in
northeast Nebraska.

The OAX 12Z sounding showed a strong 52kt h85 jet and this
resulted in strong south winds gusts mostly in the 40 to 50mph
range, however we did have some higher gusts at Norfolk and
Lincoln with 53mph and Omaha had 58h mph.

Water vapor satellite imagery and lightning/obs showed some
lightning over Idaho overnight...and this was ahead of closed h5
low pressure system that have moved across Washington state.
Farther south, there is a southern portion of the upper level
trough and there is moisture streaming ahead of that across Mexico
into the southern Plains.

The mid-tropospheric pattern through Monday for the h5 trough to
deepen from Montana through Nevada with southwest flow aloft
across the southern Plains. At the surface...this progression is
pushing a cold front into the region. At 21Z...the cold front had
made it to ONL and with continue to push into northeast Nebraska
through 00z.

Through 12Z...the front will push across the forecast area.
Updated the hourly temperatures overnight with a RAP/GFS blend as
these had the best initial temperatures at midday. Temperatures
are balmy now...some 10 to 20 degrees above normal in the 40s to
nearly 60 degrees. By 10pm...we have temperatures dropping to
below freezing at KOFk, however parts of southeast Nebraska and
southwest Iowa are still in the 40s and 50s. Between 4am and 7am
we have the temperatures falling to near or below freezing at
KLNK/KOMA/CBF with temperatures in the mid to upper 40s still at
FNB.

Visible satellite imagery and observations show low clouds
fl010-020 over southern Kansas into Oklahoma. This is where the deep
moisture with 10+ deg C dewpoint temperatures were progged to be.
h85 winds are forecast to increase from 45 to 55kts through 00z
into southern Nebraska. Meanwhile, low level moisture increases
with 4 to 6 deg. h85 dewpoints while the 10 to 12 deg C dewpoints
remain in KS and MO. Some of these 10 deg dewpoints get close
around 9Z then settle southward.

The precipitation starts as drizzle then due to the lack of cold
air/ice...freezing drizzle where temperatures are below freezing.
There chance for light accumulations are slight before 06Z...with
the precipitation area increasing between 06-09Z and through 12Z
in sync with the surge of deeper moisture. The front then settles
farther south between 12-18Z and the better precipitation begins
to shift eastward with north winds 15 to 30 mph across the area
and falling temperatures.

Left the winter weather advisory in place from midnight to noon.
Ice amount will vary from a trace to a tenth of an inch. Higher
amounts...0.05 or more tend to be from Ft. Calhoun toward South
and into west central Iowa... with a trace to 0.04 elsewhere.
Light snow of an inch or less is possible in northeast Nebraska.

Through Tuesday the large h5 high pressure system over the
southeast U.S. and the Atlantic remains in place and the H5 trough
tries to push eastward, however the northern stream does make some
progress while the southern stream remains over the southwest
U.S.

For Monday night into Tuesday, there are some differences in the
models, however, the general risk for another round of ice and
some light snow is for 1 to 3 inches of light snow in northeast
Nebraska...light icing amounts for east central Nebraska and some
.1 to .2" icing possible in southeast Nebraska and southwest Iowa.
The h85 flow of the NAM is very favorable for the icing. The GFS
is less aggressive and the EC is more aggressive, however more in
IA and MO compared to Nebraska and southwest Iowa. May need
another advisory to cover this, however it may start Monday
evening and did not want to blanket and advisory for a long period
of time when we did not have freezing drizzle occurring.

.LONG TERM...(Tuesday night through Sunday) Issued at 345 pM CST
Sun Feb 18 2018

Highs Wednesday should top out in the 20s with 30s for Thursday.
Thursday through Saturday we have chances of precipitation with a
mix due to highs in the 30s and 40s Friday and Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 541 PM CST Sun Feb 18 2018

Deteriorating conditions are expected through the evening as MVFR
cigs near FL015 develop by 06Z at all eastern Nebraska TAF sites.
Then areas of drizzle are expected from 06Z through 18Z for parts
of the area, with temperatures dropping below freezing causing
Freezing Drizzle to be the primary precipitation type for several
hours at all sites. Occasional IFR cigs could occur with areas of
heavier drizzle. Also, north winds will increase into the 15 to
25kt range from 06Z to 18Z, but then diminish somewhat Monday
afternoon.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from midnight tonight to noon CST Monday
     for NEZ012-015-017-018-030>034-042>045-050-051.

     Winter Weather Advisory from 3 AM to noon CST Monday for NEZ052-
     053-065-066-078.

     Winter Weather Advisory from 6 AM to noon CST Monday for NEZ067-
     068.

IA...Winter Weather Advisory from midnight tonight to noon CST Monday
     for IAZ043-055.

     Winter Weather Advisory from 3 AM to noon CST Monday for IAZ056.

     Winter Weather Advisory from 6 AM to noon CST Monday for IAZ069-
     079.

&&

$$

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



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