Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 200432

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1132 PM CDT Wed Sep 19 2018

.SHORT TERM...(Tonight through Saturday)
Issued at 318 PM CDT Wed Sep 19 2018

Mid-afternoon observational data clearly define the synoptic
front which is quasi-stationary from far southwest IA to between
Omaha and Lincoln into central NE near or north of Broken Bow. To
the south of the boundary, the air mass is hot and moist with
estimated MLCAPE values of 2000-2500 J/kg per latest SPC
mesoanalysis. The primary concern late this afternoon into this
evening is whether convergence along the boundary will be
sufficient to initiate and sustain thunderstorms. Several runs of
the HRRR have indicated isolated storm development between 6 and 7
PM immediately north of the front between O`Neill and Norfolk.
Should that scenario unfold, forecast soundings indicate an
environment supportive of supercell storm modes with a risk for
large hail, damaging winds, and perhaps a brief tornado.

Thunderstorm chances will continue overnight across northeast NE
within a strengthening low-level warm-advection pattern occurring
ahead of a vigorous mid-level trough moving into the northern High

Tomorrow into tomorrow night (Thu/Thu night), the short-wave
trough will translate through the northern Plains into upper MS
Valley in tandem with a 60-70 kt mid-level jet streak. An
associated surface low initially over central NE tomorrow morning
will deepen while developing into east-central MN by tomorrow
evening. Meanwhile, a trailing cold front will advance southeast
through our area during the afternoon and evening hours. Low-level
uplift along the front coupled with the influence of height falls
attendant to the mid-level trough will foster a broken band of
thunderstorms by afternoon along the front. Given a modestly
sheared and unstable environment, the setup will favor a few
strong to severe storms capable of damaging winds and hail. Some
heavy rainfall potential exists, but the progressive nature of the
front should preclude a more substantial flash flood threat.

On Friday, a cooler, continental air mass will overspread the
region with gusty northwest winds persisting into the afternoon.
Highs will be in the 60s. By Saturday, a lee cyclone will deepen
over the northern High Plains which in turn will draw a warmer air
mass into the mid MO Valley with highs around 70 or the lower

.LONG TERM...(Saturday night through Wednesday)
Issued at 318 PM CDT Wed Sep 19 2018

An initially zonal, mid-level flow regime across the north-central
U.S. this weekend will amplify early next week as a short-wave
trough tracks from the Pacific Northwest into the northern Plains.
That upper-air system will be attended by a cold front which is
expected to advance through the mid MO Valley on Monday. High
temperatures ahead of the front on Sunday and Monday are expected
to be in the 70s with an increasing chance of showers and
thunderstorms by Monday afternoon into Monday night with the
passage of the front.

Another vorticity lobe is forecast to move through the central
Plains on Tuesday within the base of an intensifying longer-
wavelength trough over the central CONUS. That feature will yield
continued rain chances into Tuesday. Otherwise, it appears that
the large-scale pattern will favor cooler temperatures during the
middle to latter part of the upcoming week.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1135 PM CDT Wed Sep 19 2018

A few TSRA did affect KOFK this evening, and it looks like more
could for the overnight hours. However, will only mention VCTS
at this time. BKN clouds at 7000 feet or higher should affect KOMA
and KLNK much of the overnight. Expect a band of TSRA to develop
and move southeast to KOMA and KLNK Thursday afternoon with MVFR
or lower conditions in precipitation. TSRA will be along and
behind a cold front, that will switch winds to the northwest.




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