Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 261754

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1254 PM CDT THU MAY 26 2016

Issued at 1149 AM CDT Thu May 26 2016

Enhanced risk for severe still is forecast by SPC Day 1 outlook
for southeast Nebraska, with slight risk for much of the rest of
eastern Nebraska and southwest Iowa. Majority of hi-res mesoscale
model output suggests storm initiation will occur early this
afternoon, before 20Z, in southeast Nebraska. Expansion north and
east will occur through the afternoon. Storms will likely fire
along outflow from earlier convection and tied to storms currently
over northeast Kansas, probably from Falls City to Lincoln and
points southwest. High instability with surface based CAPE over
2000 J/KG with west-southwest effective shear vectors 40 to 50kt.
Low level wind flow and helicity suggests a low tornado potential
initially, but certainly not zero, with highest initial tornadic
threat farther southwest in Kansas. As synoptic warm front lifts
north through late afternoon, low level hodographs show enhanced
tornadic threat in southeast Nebraska. So for now, will continue
with our trend for increasing threat for storms and severe through
the afternoon.


.SHORT TERM...(today through Saturday)
Issued at 431 AM CDT Thu May 26 2016

...Enhanced Risk of Severe Storms Today and Tonight...

Rather complex forecast setting up for today and tonight with a
substantial risk of severe weather. Apologize for the delay of the
discussion, but got a late start on the forecast due to severe
earlier convection that produced large hail and wind gusts up to
58 mph. These initial storms have pushed east of the area as the
weak upper level impulse moves into the Mississippi river valley.
A weak surface trough made a push into the forecast area, and it
may still remain across western portions of MN into northeast NE,
but really this feature will probably become very diffuse in our
area today. Meanwhile, an 08z subjective analysis indicated the
surface low remained across the OK panhandle, with a
stationary/pseudo warm front extending east northeast into
northeast KS and northern MO. Convection continues to bubble up
along the eastern edge of the boundary taking advantage of the
southern end of the aforementioned upper wave.

It`s important to say that the various high-res CAMs all offer
varying solutions today of the eventual placement of any severe
clusters, which makes the forecast even more difficult. There is
one weak upper wave moving through western NE early this morning.
This is generating mostly showers, although there is a lightning
strike showing up in the most recent imagery. This may bring a
slight chance of thundershowers along/north of I80 this morning,
but these would not be severe. The CAMs do suggest that convection
could develop by 13-14z along the boundary to our south, which
then begin to lift north through mid morning. There is a risk that
some of these could bubble up enough to produce some hail in
southeast NE 14-16z, and could become stronger and potentially
severe by 16-18z taking advantage of the building instability with
daytime heating. surface dewpoints were in the mid 50s to lower
60s, but should recover into the mid to upper 60s, which will
couple with h85 dewpoints of 12 to 14 degrees. if this earlier
convection develops as forecast, then it could have an impact on
later convection in the area as well, and could delay an onset of
the second round until later in the evening. although, the gfs
allows the warm front to move a little further north, which
develops additional convection in the platte river valley during
the afternoon, again making the forecast very challenging pinpoint
the details.

SPC has placed the southern 2/3 of the forecast area in an
enhanced risk of severe storms, with all modes of weather
possible, including a 15% probability of damaging winds, a 30%
probability of very large hail, and a 10% probability of
tornadoes. This is generally along and south of a line from
Albion, NE to Harlan, IA. Given the proximity of the warm front
with developing storms potentially along it, and environmental
parameters of bulk shear of 40-50 knots, ample moisture, and very
high instability, have no doubt we`ll eventually have a severe
threat later today.

As the front continues to lift northward overnight, will have a
continued likely chance of storms moving through the area, but we
may see a decreasing trend after midnight.

Storm chances continue Friday into Saturday as the upper low slowly
transitions through the region. Still a marginal risk of severe
weather on Friday, but that threat shifts generally shifts east of
the area by Saturday.

.LONG TERM...(Saturday night through Wednesday)
Issued at 431 AM CDT Thu May 26 2016

Opted for a dry Saturday night as I believe we could be in
between systems. Rain chances increase again by Sunday and
continue on and off through the end of the period.


.AVIATION...(18Z TAFS for KOMA...KLNK...KOFK through 18Z Friday)
Issued at 1250 PM CDT Thu May 26 2016

Showers and thunderstorms will begin to pop up across the region
this afTernoon. Storms could begin in KLNK as early at 19Z and
move into KOMA and KOFK later this afternoon and evening. Showers
and thunderstorms will continue well into the overnight hours
before clearing and potentially allowing light fog to develop
early Friday morning.


.OAX Watches/Warnings/Advisories...


SHORT TERM...dewald
LONG TERM...dewald
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