Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 231738
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1238 PM CDT TUE AUG 23 2016

.UPDATE...
Issued at 1055 AM CDT TUE AUG 23 2016

Have updated the forecast for the latest trends. Cluster of
elevated thunderstorms continues to lift northeastward through NE
Neb this morning. This activity was closely tied to mid-level
shortwave trough and associated 40-50 H5 height falls. This system
and associated convection is expected to continue to lift to the
northeast out of the area through early afternoon. The main
forecast concern then is any redevelopment in the wake of this
activity. Latest short term guidance indicates that forcing this
afternoon will largely be for subsidence in the wake of the
morning shortwave trough. This along with a lack of a discernible
surface boundary in the area limits confidence in redevelopment.
Modifying the 12Z KOAX sounding indicates that with continued
moistening that the atmosphere will become moderately to strongly
unstable this afternoon with around 1500-2000 J/kg of MLCAPE.
Given highs in the lower to mid 80s does also remove a good deal
of the MLCIN as well. Thus although widespread storm redevelopment
appears unlikely, some isolated redevelopment is possible. There
appears to be two primary areas for this redevelopment. The first
would be over north central Nebraska where the cold front
/currently over western SD/ will move into the area. The second
area is along the trailing outflow from the current activity.
Overall lowered pops from this afternoon and into tonight as
widespread activity isn`t expected. If storms do redevelop, which
a few likely will, some stronger storms still appear likely but
weak wind profiles above 850 mb will likely lead to a messy storm
mode and only short-lived rotating thunderstorms with a wind and
hail threat.

&&

.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...(18Z TAFS for KOFK...KLNK and KOMA.)
Issued at 1232 PM CDT TUE AUG 23 2016

MVFR ceilings continue to work through the TAF sites this morning,
but these will likely scatter this afternoon and lift to near or
above 3000 feet. Have removed all mention of rain/thunder from the
TAF forecast due to uncertainty in redevelopment this afternoon,
and expected isolated nature if anything does occur. Surface cold
front will move through all 3 TAF sites overnight and switch the
winds to the northwest. We may see some additional MVFR ceilings
overnight tonight and into Wednesday morning.

&&

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

&&

$$

UPDATE...Boustead
SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Boustead



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