Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 010022

Area Forecast Discussion
National Weather Service Omaha/Valley NE
722 PM CDT FRI SEP 30 2016

.SHORT TERM...(tonight through Monday)
Issued at 325 PM CDT FRI SEP 30 2016

Manual analysis of 12z upper-air data revealed a deep-layer
cyclone over the Ohio Valley, a weak ridge over the southern and
central Plains and a substantial trough off the Pacific Coast. An
axis of low-level moisture wrapping around the northern and
western periphery of the Ohio Valley cyclone is evident in
afternoon visible satellite by a westward-expanding strato-cumulus
deck across Iowa. As this synoptic system continues north toward
the Great Lakes tonight, this moisture surge will overspread our
area, resulting in areas of fog and low clouds. These low clouds
may be slow to burn off on Saturday, especially along and east of
the Missouri River, which will impact afternoon high temperatures.

The low pressure system will begin to accelerate east-northeast
from the lower Great Lakes into New England Sunday into Monday in
response to the progression of an upstream trough through the
Interior West. This upper-air pattern evolution will promote the
deepening of a lee trough over the High Plains Sunday and eventual
cyclone formation over the northern or central High Plains by
Monday. The cyclogenesis will foster the poleward flux of an
increasingly moist and unstable boundary layer through the Great
Plains within a strengthening southerly low-level flow regime.
However, we will maintain a dry forecast through Monday as the
strongest large-scale forcing for ascent remains to our west.

.LONG TERM...(Monday night through Friday)
Issued at 325 PM CDT FRI SEP 30 2016

The 12z runs of the ECMWF and GFS continue to indicate differences
in the evolution of the western U.S. trough as it emerges into the
Plains Monday night into Wednesday. The GFS depicts a much more
intense mid-level trough and associated deeper surface cyclone
tracking across the northern Plains Tuesday, whereas the ECMWF
suggests a less dynamic synoptic system. However, both solutions
do indicate an associated cold front advancing through the mid
Missouri Valley late Tuesday afternoon into early Wednesday with
an increased chance of thunderstorms along and ahead of the front.
Severe weather potential Tuesday afternoon into Tuesday night will
ultimately be dictated by the timing and intensity of the synoptic
system, as well as any deleterious effects on instability by residual
clouds and early-day convection.

The cold front is expected to shift east of the area on Wednesday
with a surface high building into the region Thursday and Friday.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 703 PM CDT Fri Sep 30 2016

VFR conditions for this evening. MVFR conditions will work into
eastern Nebraska mainly after 09z with improvement after 15z-19z.
Satellite imagery shows MVFR cigs in parts of central Iowa on the
west side of the storm system over southern Indiana and northern
Kentucky. A cirrus shield has been also increasing over the
Central Plains. Extent of low clouds and fog will be the main
concerns tonight. For now included MVFR conditions for fog/cigs
at all three sites. Short range models indicate pockets of lower
visibilities/cigs possibile, however not confident to include in
the TAF at this time.


.OAX Watches/Warnings/Advisories...


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