Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 241735

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1235 PM CDT Sun Sep 24 2017

.SHORT TERM...(Today through Tuesday)
Issued at 308 AM CDT Sun Sep 24 2017

A prominent mid-level trough centered over the Great Basin early
this morning will edge east into the central Rockies by tonight
before ejecting northeast across the northern and central Plains
Monday and Monday night. Meanwhile, the associated surface front
which stretches from central MN through northeast NE into
northwest KS as of 07z will begin to advance east/southeast later
today into tonight. The front is expected to eventually progress
south of our forecast area Monday night into Tuesday morning.

A band of post-frontal showers and a few thunderstorms are ongoing
early this morning across western parts of SD/NE/KS, aided by a
belt of forcing for ascent associated with a vorticity lobe
pivoting through the eastern semi-circle of the parent midlevel
trough. The passage of this perturbation into the northern High
Plains will encourage the movement of the deeper-layer cold front
into the forecast area this afternoon into tonight with a
corresponding increase in measurable precipitation chances along
and behind the boundary.

Clouds will increase across the pre-frontal warm sector today.
But given the continued presence of an anomalously warm air mass,
afternoon temperatures will rise into the mid to upper 80s. There
will likely be a sharp temperature gradient across the front by
afternoon with readings in our far northwest counties hovering in
the 60s.

Tonight into Monday night, the cold front will slowly progress
southeast through the forecast area, yielding a prolonged period
of shower and thunderstorm activity, primarily on the cool side of
the boundary. Highest storm-total precipitation amounts are
expected across northeast NE where 2.0-2.5 inches are possible.
As we have eluded to in past discussions, mesoscale processes will
likely contribute to locally higher amounts and some flooding
remains possible.

Precipitation chances should begin to diminish from north to south
across the area late Monday night into Tuesday as the cold front
continues south into KS and MO. As far as temperatures are
concerned, we expect a fairly substantial gradient across the
forecast area again on Monday with readings ranging from around
80 over far southeast NE and southwest IA to upper 50s near the
NE-SD border. By Tuesday, afternoon highs will be mainly in the
60s areawide.

.LONG TERM...(Tuesday night through Saturday)
Issued at 308 AM CDT Sun Sep 24 2017

Medium-range guidance remains in relatively good agreement through
mid week, depicting a shortwave trough over Ontario with a closed
midlevel system over the lower CO Valley. However, by late week,
model solutions begin to diverge. The ECMWF develops a deep low
over the Great Lakes whereas the GFS, GEFS, and Canadian models
suggest a more progressive pattern with the lower CO Valley low
ejecting into the central Plains and undercutting a longer-
wavelength ridge over central Canada. The upshot is that
predictability from about Friday into next weekend is low. We will
maintain a generally dry forecast with slightly below normal


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1231 PM CDT Sun Sep 24 2017

Deteriorating aviation conditions are expected through Monday
morning across all of eastern Nebraska. Scattered showers or an
isolated thunderstorm are expected to develop by 00Z near all
sites, and continue off-and-on through 18Z Monday. Generally VFR
conditions with this activity. However as a cold front drifts
southeast, southerly winds will turn northwest or north, and will
draw in MVFR to IFR cigs. Timing of the front is still in
question as any convective activity could interrupt or accelerate
progression. Expect MVFR cigs at KOFK before 00Z, then IFR after
06Z, while KOMA and KLNK will likely hold VFR cigs through 06Z,
with potential IFR cigs before 12Z.




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