Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
014
FXUS63 KOAX 240528
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1128 PM CST Fri Feb 23 2018

.UPDATE...
Issued at 940 PM CST Fri Feb 23 2018

Strengthening lower to mid-tropospheric warm advection is
fostering the development and northward spread of light
precipitation south of I-70 in KS as of 03z. As the associated
mid-level trough translates through the Four Corners toward the
High Plains overnight, expect the warm-advection regime and
attendant precipitation shield to progressively overspread our
forecast area. Latest model guidance continues to indicate a high
probability for freezing drizzle or light freezing rain south of a
line from Lincoln and Omaha to Harlan, IA through mid morning with
mainly snow over northeast Nebraska. By around midday, these data
suggest the "all snow" line collapsing southeast toward Omaha and
Lincoln with a continued southeastward shift of this transition
zone through the remainder of the afternoon.

While forecast soundings indicate thermal profiles supportive of
that scenario, saturation may not extend upward into the
dendritic-growth zone. As such, the freezing rain could linger a
bit longer than the model guidance would otherwise suggest. In
general, the current precipitation-type forecast is in reasonably
good shape and we are not inclined to make any substantive
changes.

It appears that the primary deformation-zone-related snow band
will remain to the west of our forecast area and as such, we may
be a bit high on snowfall amounts over northeast NE. As mentioned
above, we will leave the forecast "as is" and re-evaluate
overnight.

&&

.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 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 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.

&&

$$

UPDATE...Mead
SHORT TERM...Miller
LONG TERM...Miller
AVIATION...Mead



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.