Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 200938

Area Forecast Discussion
National Weather Service Omaha/Valley NE
338 AM CST Fri Jan 20 2017

.SHORT TERM...(today through Sunday)
Issued at 338 AM CST Fri Jan 20 2017

Manual 00z upper-air analysis and early-morning water vapor
imagery indicated a high-amplitude wave pattern present over the
CONUS with the primary feature of interest being a short-wave
trough presently near the Four Corners region. This disturbance
will undergo amplification as it ejects northeast through the
central Plains into mid MO Valley by tonight. In the low levels,
an evolving area of low pressure over the central and southern
High Plains today will develop into eastern NE/western IA late
tonight/early Saturday, in tandem with the parent upper-air

Surface observations indicate a saturated or near-saturated
boundary layer this morning across the central Plains into Ozarks,
to the north of the evolving surface low over the southern High
Plains. Persistent low-level warm advection and moisture flux will
maintain areas of fog and drizzle today with little diurnal
temperature range. Tonight, large-scale forcing for ascent will
strengthen through a deeper layer, yielding a transition from
drizzle to rain. Highest PoPs will stretch from our central into
northeast counties within a deformation band developing to the
north of the migratory surface low. Forecast soundings indicate
that the boundary layer will remain sufficiently warm to support
an all-rain event.

Saturday, we may see some breaks in the clouds by afternoon in
the wake of the aforementioned weather system moving into the
upper Midwest. West or northwest downslope flow in the low levels
and the potential for slightly greater diabatic warming (compared
to previous days) will yield afternoon highs in the mid to upper

Sunday, an intense mid-level trough will progress from the south-
central into southeast U.S. with any associated precipitation
remaining to our south. This system, in concert with a weaker
polar-branch cyclone over the upper Great Lakes, will contribute
to the advance of a slightly cooler --but still above normal-- air
mass into the mid MO Valley.

.LONG TERM...(Sunday night through Thursday)
Issued at 338 AM CST Fri Jan 20 2017

The main focus in the long term remains the potential for
accumulating snowfall in the Tuesday-Tuesday night timeframe. The
suite of 00z medium-range guidance indicates that a potent mid-
level trough will traverse the Interior West on Monday prior to
forming an upper low over the central Plains or mid MO Valley
Tuesday into Tuesday night. While there are slight differences
between the deterministic models in the track and intensity of
this system, confidence in a strong synoptic-scale low over the
central U.S. on Tuesday remains high at this juncture. Current
indications are that the highest probability of accumulating
snowfall will exist across the northern part of our CWA with a
mixture of rain and snow or all rain farther south.

A continental-polar air mass will be drawn south through the mid
MO Valley on Wednesday in the wake of the departing synoptic
cyclone, yielding cooler and drier weather through the remainder
of the work week.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1137 PM CST Thu Jan 19 2017

Variable cigs/vsbys between LIFR and MVFR will persist for a few
more hours, but low level moisture continuing to advect into
eastern Nebraska suggests both cigs and vsbys will drop to LIFR or
VLIFR categories by 09Z and linger through 18Z. Some improvement
is likely then, but still IFR conditions will rule. Areas of
drizzle are forecast to develop by late afternoon and continue
through Friday evening, reinforcing the low cigs and vsbys.


NE...Dense Fog Advisory until 9 AM CST this morning for NEZ011-012-

IA...Dense Fog Advisory until 9 AM CST this morning for IAZ043-055-



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