Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 232111
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
311 PM CST Fri Feb 23 2018

.SHORT TERM...(Tonight through Monday)
Issued at 310 PM CST Fri Feb 23 2018

The main forecast concerns are in regards to snow and ice amounts,
with the winter weather system that will affect the area starting
late tonight and continuing through the day on Saturday.

Fairly complex/messy forecast with mixed precipitation across the
forecast area starting late tonight. The zero degree isotherm at
850 mb this morning stretched from western KS into southeast NE
then extended from southwest to northeast across IA. There was a
fairly tight baroclinic zone in the lower and mid troposphere
across the central part of the Plains. At 500 mb, a trough was to
the west over the Rockies, with an area of height falls strongest
over southern NV this morning. Two main areas of strong winds were
noted at 300 mb, one digging southeast from the CA coast and
another that extended from the Four Corners region to northeast of
the Great Lakes region. Water vapor satellite imagery early this
afternoon showed an elongated disturbance from southwest WY into
UT and northern AZ. Surface analysis at 21z showed high pressure
across much of the northern and central parts of the Plains, with
low pressure organizing over northeast NM and southeast CO.

Precipitation should develop over the area later tonight as
moisture profile increases due to development of a weak low level
jet, mid level isentropic upglide and diffluent upper level flow.
Moisture depth initially in the southern parts of the area may
not be deep enough to produce more than freezing drizzle, but
lapse rates aloft will be increasing. Thus some showery type
precipitation may develop as well. The 19Z RAP layer composite
reflectivity forecasts suggest precipitation increasing after 08z
in our western and northern counties. All of eastern NE and
southwest IA counties served by the Omaha office are in a Winter
Weather Advisory from 3 am to 6 pm Saturday. Models have decreased
their QPF amounts a little, and thus we have lowered expected
snow amounts a bit. Northeast NE should see mainly snow, mainly 3
to 5 inches, but possibly approaching 6 inches. 700-750 mb
specific humidity values are still expected to be around 3 g/kg
from the GFS, with about a 9 to 12 hour period of moderate lift
and some elevated frontogenesis. Will need to watch for potential
banding of snow, which could enhance amounts in our area.

Farther south, ice accumulations are the issue with around a
tenth of an inch to near two tenths possible. These numbers are
solidly in advisory levels. Ice aloft is generally lacking through
the morning in southeast NE and southwest IA, so if that holds
true snow amounts will be less than farther north, and that is how
our current snow amounts are depicted. Areas near the KS and MO
borders could reach above freezing during the day Saturday, then
turn colder as winds shift to the northwest.

Expect precipitation to be ending by around 6 pm, but there is a
small chance that light freezing drizzle could linger a bit longer.
The period from Sunday into Monday looks dry with a warming trend.
Highs Monday should reach mainly into the 40s with some 50s near
the KS border.

.LONG TERM...(Monday night through Friday)
Issued at 310 PM CST Fri Feb 23 2018

From Monday night through Tuesday evening, have kept the forecast
dry. The 500 mb pattern still favors a trough from south central
Canada back to toward southern CA. Our area should remain in
southwest or westerly flow aloft, with a weak split flow pattern.
Model spread starts to develop by mid week and then increases by
late week, so confidence drops to below average by Friday. Still,
the period from Wednesday into Thursday looks somewhat active
based on a model blend. By Friday, is appears that a mid level
ridge will build over the Plains, at least temporarily.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1119 AM CST Fri Feb 23 2018

A deck of MVFR to IFR clouds will continue to spread south across
the region through the early afternoon hours. Expect ceilings
will rise to VFR levels by this evening, before dropping down
once again around 06Z ahead of the next wintry system. Current
guidance suggests precip will begin around 10Z-12Z with primarily
snow at KOFK and mostly freezing rain/drizzle at KOMA and KLNK,
possibly mixing with light snow through the day Saturday.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from 3 AM to 6 PM CST Saturday for
     NEZ011-012-015>018-030>034-042>045-050>053-065>068-078-
     088>093.

IA...Winter Weather Advisory from 3 AM to 6 PM CST Saturday for
     IAZ043-055-056-069-079-080-090-091.

&&

$$

SHORT TERM...Miller
LONG TERM...Miller
AVIATION...KG



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