Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 231115
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
615 AM CDT TUE AUG 23 2016

.SHORT TERM...(today through Thursday)
Issued at 345 AM CDT TUE AUG 23 2016

Forecast concerns in the short term will be increasing
thunderstorm chances today and tonight across the forecast area
and south of I80 Wednesday...along with the potential for severe
weather and heavy rain. These concerns linger into later Wednesday
and Wednesday night near the Kansas border.

The h5 pattern has a closed low over Alberta with a series of
embedded shortwaves farther south over southwest Nebraska...
southern Colorado...southern Nevada...and southern California. As
the low over Alberta moves into Saskatchewan...a shortwave from
southwest Nebraska moves into central Nebraska. A cluster of
storms over southwest Nebraska associated with the shortwave is
lifting northeast and should approach the western part of the
forecast area in the 12 to 13Z time period.  Through 18z...this
shortwave lifts northeast into southeast South Dakota with
increasing warm air advection/theta-e advection ahead of it. The
ESRL HRRR is not available...however the operational
HRRR/RAP13/SPC HRRR/NAM/SREF/EC/UKMet track scattered thunderstorms
northeast with the GFS remaining mainly dry. Forecast soundings
show warm air in place in the lower and mid levels thus storms
would be elevated initially. By early afternoon...CAPE Values are
1000 to 2000j/kg and by 00z the CAPE has increased to
2000-4000j/kg with the inhibition eroded. 0-6km bulk shear is 25
to 30kts and the 0-3km bulk shear magnitude increases to 35kts in
northeast Nebraska by 18Z...45kts at 21Z...and the max shifts east
into northern Iowa. Will mention scattered thunderstorms with the
shortwave this morning. With heating and continued moisture
convergence increase pops over much of the forecast area in
eastern Nebraska and western Iowa with storms becoming more
surface based. The forecast soundings shows veering of winds
aloft. Freezing levels are not too high as well. All said...all
modes of severe weather will be possible. Precipitation and
clouds could limit heating and also outflow boundaries from
morning storms could come into play, thus affecting the potential
for severe weather this afternoon and tonight. Much of the area is
in the slight risk for severe storms.

Precipitable water values increase to 1.5 to 2.0 inches by 18z
and linger through 06z for all by the northeast third of the
forecast area. Some spots have had decent rains over the last
three weeks, while others could use some. 6hr flash flood guidance
is mostly in the 3 to 4 inch range. Forecast soundings slow the
movement of the storms this evening and the h85 boundary is slow
to push south with deep moisture pooled ahead of it. The direction
of the h85 is more veered...however an h7 jet and upper level
support could lead to thunderstorm redevelopment and training of
storms tonight. The qpf progs are a bit variable with a couple of
models pointing more with heavy rain toward Iowa and others
southeast Nebraska into southwest Iowa and points south. WPC has
us in a broad area of slight risk for excessive rain as training
of storms could result in localized 3 to 5 inch rains.

The surface and h85 boundary stall near the Nebraska/Kansas and
Iowa/Missouri borders Wednesday with another shortwave moving
through the flow. This will linger thunderstorm chances in this
area with a slight risk for severe storms and a marginal risk for
excessive rainfall. The heavy rain potential seems pretty good
near the Kansas border Wednesday afternoon and Wednesday evening
with the stalled front. Will need to see how far south the front
makes it and may need to increase pops in the far south for
Thursday.

Highs today and Wednesday should top out in the 80s with 70s for
Thursday.

.LONG TERM...(Thursday night through Monday)
Issued at 345 AM CDT TUE AUG 23 2016

The h5 trough moves through Friday night and Saturday so continue
with likely thunderstorms for parts of the area. The flow becomes
more zonal with weak perturbations in the flow...thus cannot rule
out isolated to scattered storms Sunday through Monday.

&&

.AVIATION...(12Z TAFS for KOFK...KLNK and KOMA.)
Issued at 615 AM CDT TUE AUG 23 2016

Scattered TSRA over parts of south central Nebraska should continue
to lift northeast this morning. MVFR or lower ceilings and vsbys
will be possible in pcpn. There is quite a bit of uncertainty as
to how much if any TSRA will affect KLNK and KOMA this morning.
For now will not mention any pcpn at KOMA before 21z...and overall
chances at KLNK this afternoon seemed too low to mention at this
time. But will amend as needed. Southerly winds had dropped off
overnight...but should increase again after sunrise today.

&&

.OAX Watches/Warnings/Advisories...
NE...None.
IA...None.
&&

$$

SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Miller


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