Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 201658

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1158 AM CDT TUE SEP 20 2016

.SHORT TERM...(today through Thursday)
Issued at 317 AM CDT TUE SEP 20 2016

Warm temperatures the next couple of days with a return to
thunderstorm chances Wednesday afternoon into Thursday are the
primary concerns of this forecast.

Surface high pressure was settling into eastern Nebraska and western
Iowa this morning, behind cold front that had slipped south into
northern Kansas and northern Missouri. Strong westerlies aloft
across the northern tier of states was inducing lowering pressures
in the Northern High Plains, promoting southerly return flow across
the Plains this morning. As such, cold front is forecast to
surge/bridge north of our CWA early in the day with gusty south
winds and rapid increase in low level moisture in its wake. Lower
70s dew points noted in eastern Kansas and western Missouri are
scheduled to spread across most of our area this afternoon,
contributing to surface-based CAPE values over 2500 j/kg along the
Missouri River and east. However building heights leading to
pronounced inhibition and lack of mid level forcing suggests no
convection expected here. High temperatures between 85 and 90 should
be common this afternoon, with heat indices in the middle 90s in
many areas.

Southerly flow and dew points remaining in the mid to upper 60s
tonight will keep lows from falling very far into the 60s, and will
likely hold in the lower 70s over the southern half of the CWA.

Things become a little more interesting later Wednesday afternoon
and night as shallow mid level ridging breaks down somewhat with
approach of shortwave from the southwest. GFS and ECMWF have been
consistent in showing this feature while NAM maintains a Wednesday
night arrival. Our forecast is and has been more in-line with GFS
solution over the last several days, and run-to-run consistency of
that model inspires maintaining the status quo. Thus, expect a
gradual weakening of inhibition through the day as mid level
temperatures cool with approach of shortwave. Lowering heights
should also promote a gentle southward drift of surface front into
northeast Nebraska by the afternoon. Mid to upper 60s dew points
will remain available to contribute to over 2000 j/kg of SBCAPE near
and south of the front with bulk shear increasing to near 30kt. So
expect scattered  convection to become more likely as we head toward
late afternoon, allowing time for cap to erode. There is some severe
potential given instability, but only modest shear suggests
maintaining threat will be difficult. Uptick in shear with
increasing low level jet during the evening will be offset by loss
of heating/instability, but certainly will see continued storm
development overnight before shortwave exits our area Thursday

Overnight and morning convection will play havoc with surface
boundaries, but best bet is cold front will begin lifting back north
again Thursday afternoon as heights rise in wake of shortwave and
ahead of larger upper trough drifting into the Rockies. Could see
some redevelopment Thursday afternoon, but chances are much more

.LONG TERM...(Thursday night through Monday)
Issued at 317 AM CDT TUE SEP 20 2016

Evolution of western low/trough into the weekend and the affects on
our weather remains the primary longer term forecast highlight. GFS
and ECMWF again have been fairly consistent in regards to sensible
weather for our part of the world this weekend, while progression of
at least part of western trough/low has shown some inconsistency.
This morning, there is some consensus that a significant chunk of
mid level energy will be ejected into the Northern Plains on Sunday,
with our area on the back side of system by Sunday evening into
Monday. Ahead of the trough, lingering convection Thursday night
will likely be shut off by mid level warming under rising heights in
sharpening ridge axis on Friday. Moisture plume and instability axis
will gradually push east as wave lifts into the Northern Plains, and
is currently scheduled to arrive in eastern Nebraska and western
Iowa on Saturday before shifting east by Sunday night. We will see
continued chances for showers and thunderstorms under this plume,
but severe risk should be low given saturated atmosphere and lack of
significant instability. However heavy rain is possible given slow
eastward progression of moisture, potential training of storms, and
precipitable water values rising into the 175-200 percent of normal


Issued at 1156 AM CDT TUE SEP 20 2016

Winds will again be the primary issue at all TAF sites. South
southeasterly winds at 12-20 knots initially, with gusts diminishing
by 23-00z. Non convective LLWS develops by 21/04-06z with winds
around 2000 from 35 to 45 knots, which ends by 21/15-16z.


.OAX Watches/Warnings/Advisories...


LONG TERM...Dergan
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