Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 270307

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1007 PM CDT TUE JUL 26 2016

Issued at 955 PM CDT Tue Jul 26 2016

The latest SWO has the marginal risk for severe storms into
northeast Nebraska. Late this evening...a line of severe storms
was rolling through parts of South Dakota and northern Nebraska.
The instability and moisture are most favorable where the storms
are now/western Nebraska. The eastern end of the line toward
Verdel is weaker. As a weak shortwave moves into the
area...0-3km shear increases, moisture will accompany it, and
there will be some favorable deep layer shear and downdraft CAPE.
Gusty winds will be possible with the storms. The 00Z NAM takes
the bulk of the storms west of the area...meanwhile the ESRL
HRRR/Operational HRRR bring the storms a little farther east
before weakening 10-12Z.


.SHORT TERM...(tonight through Friday)
Issued at 326 PM CDT Tue Jul 26 2016

High pressure is still dominating the area, with quiet and mild to
seasonable temperatures.  Subjective 12Z upper air analysis
indicates mainly zonal flow across the northern tier of the US, with
a few weak embedded shortwaves, including one in MT and another from
MN through IA/MO.  Weak upper-level flow was noted, with upper-level
jet well north into Canada toward New England.  At 850mb, a dry air
intrusion was noted from MN into the mid- to lower MO River valley,
with moisture returning through KS toward the High Plains of
NE/SD/ND.  Surface high at 19z was centered in eastern IA, with
return flow finally sneaking into central to northeast NE.

Main forecast concern is shower/thunderstorm potential tonight
through Friday.  Thunderstorms are ongoing in SD, and RAP/HRRR have
some of the better current handling of the storms in both their
coverage and their weakening trend.  Meanwhile, storms also are
developing from the Black Hills to the foothills.  The more westerly
batch of convection is the one associated with the shortwave
analyzed in MT at 12Z and is more likely to impact our area tonight.
Still seems like precipitation will hold off until after 06Z and may
struggle to move into the drier air over eastern NE/western IA. Have
limited the southward extent of precip mention tonight and really
focused mention on northeast NE into Wednesday morning.

There may be something of a lull in activity for most of the area on
Wednesday as a weak front moves into the area, with convective
development in eastern NE/western IA on Wednesday afternoon and
expansion through the evening. Have tightened coverage of higher
POPs through the afternoon and evening, particularly to clear the
northwestern CWA more quickly and to delay onset in the southeastern
CWA until evening.  Think the marginal severe weather outlook from
SPC is about right, with weak shear and some instability, but with a
front becoming increasingly baroclinic through the evening and
perhaps providing some focus for storms.

Most models are now on the drier side on Thursday, with stabilized
air and high pressure moving in behind the front.  Have reduced POPs
and also cooled temperatures a touch.  Confidence remains quite low
for Friday, with some signals for precipitation but not much in the
way of focus, other than the presence of northwesterly flow and the
tendency for periodic shortwaves.  Have kept a mention on Friday for
now, again with temperatures on the cooler side.

.LONG TERM...(Friday night through Tuesday)
Issued at 326 PM CDT Tue Jul 26 2016

Northwesterly flow continues into Saturday, before rising 500mb
heights and a building ridge over the central US send the "ring of
fire" northward.  Held onto slight chance pops in at least some part
of the CWA into Saturday, with lingering slight chances in the
southern CWA into Sunday.  Temperatures will moderate through the
period, and by Monday and Tuesday, will again reach the 90s with
increasing humidity, pushing heat indices toward the 100s.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 739 PM CDT Tue Jul 26 2016

VFR conditions outside of any thunderstorm activity. The
environment is much more favorable in SD for storms, however
veering winds will eventually bring the storms toward Norfolk.
For now included VCTS for a few hours around 08z and will
continue to monitor how the storms hold together. Convection is
sporatic for Wed. and too low confidence on location and timing
to add thunder in the TAFS as a couple of shortwave perturbations
track across the area. Did mention vcsh at KOMA/KLNK to hint at
showers in the area.


.OAX Watches/Warnings/Advisories...


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