Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 212339

Area Forecast Discussion
National Weather Service Omaha/Valley NE
639 PM CDT WED SEP 21 2016

.SHORT TERM...(tonight through Saturday)
Issued at 310 PM CDT WED SEP 21 2016

Main forecast concern centers around thunderstorm chances tonight.
SWODY1 Slight Risk area was downgraded to a Marginal Risk for the
early afternoon update thanks to a strong capping inversion
currently in place. Latest surface analysis shows a frontal
boundary extending northeast from low pressure over southwestern
Nebraska into a weak low over southeastern South Dakota and then
the front continues northeast into southern Minnesota with a well
defined outflow boundary across central and eastern Iowa. Ahead of
the boundary, a warm, moist and unstable airmass remains in place
with surface dewpoints in the lower 70s across much of the
forecast area. Aloft, a weak impulse per water vapor imagery
continues to move northeast across central Nebraska but has yet to
aid in and convective initiation due to the strong capping
inversion in place. With the surface front making little progress
south overnight, think any convection that can develop will be in
association with strengthening southwesterly low level jet after
dark. Most recent runs of the CAM`s are fairly optimistic on
developing convection across our southwestern counties and
spreading it east through the overnight hours. Locally heavy rain
is certainly a possibility with PW`s AOA 2.0". The surface front
is forecast to slowly ooze south into our northwestern counties
around 06z tonight and move toward KOFK by 18z Thursday. This
again will be the focus for continued showers and thunderstorms
through Thursday, generally along the boundary.

A large upper trough will move into the High Plains on Friday
bringing continued warm and moist air to the region. Some late
night convection is possible in warm air advection regime but
better focus will come in the form of a cold front Saturday as the
upper trough drifts northeast into the Dakotas.

.LONG TERM...(Saturday night through Wednesday)
Issued at 310 PM CDT WED SEP 21 2016

By Saturday night, a strong mid/upper level low will be slowly
rotating east along the Canadian/North Dakota border while a large
ridge builds over the western states and another builds over the
eastern state. There do remain some model discrepancies between
the ECMWF and GFS with the GFS offering a continuous closed low
solution over the Northern Plains while the ECMWF does open the
circulation for a time being before closing it off again over the
Central Plains. In any case, this will drive a strong cold front
into the area late Saturday night providing a focus for showers
and thunderstorms which could produce heavy rain given high PW`s. Otherwise,
periods of showers and isolated thunderstorms cannot be ruled out
through the week as the closed cold low drifts overhead bringing
much cooler surface temperatures as well.


Issued at 629 PM CDT WED SEP 21 2016

Latest sfc obs showing a bndry extending from srn MN to the Neb
panhandle. Main issue is how widespread will TSRA be later this
evening. Strong cap so far is inhibiting initiation...but a sfc
bndry begins to drop south cap will weaken with TSRA forming along
the front. However...given that the environment will be more
supportive for convection to the east...suspect activity will be
just isolated/sct in nature twd midnight thru early Thursday


.OAX Watches/Warnings/Advisories...


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