Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 201807

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1207 PM CST Fri Jan 20 2017

Issued at 1155 AM CST Fri Jan 20 2017

Did a mid-morning update to continue the dense fog advisory
through Noon. STill a few sites around 1/4sm-1/2sm in dense fog,
however the majority of locations are improving steadily.


.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 18Z TAFS through 18Z Saturday morning)
Issued at 1155 AM CST Fri Jan 20 2017

Variable conditions across the TAF sites with LIFR cigs and
MVFR/VFR vsbys. Moisture remains in place through the TAF period
with continued mid/upper level support as surface low pressure
develops over the region and shifts east into Iowa Saturday
morning.  Have deteriorating conditions later this afternoon and
overnight with LIFR/IFR vsbys and cigs with fog/drizzle/light
rain. Between 12-15Z low level moisture/shows improvement through





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