Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 261728
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1228 PM CDT Mon Jun 26 2017

.SHORT TERM...(Today through Wednesday)
Issued at 321 AM CDT Mon Jun 26 2017

A more active weather pattern is developing over the next couple of
days as thunderstorm chances increase markedly Tuesday night and
Wednesday.

However precipitation chances will not be confined to those periods
as we already have showers and isolated thunderstorms on radar
this morning. Shortwave traveling southeast from the Dakotas into
eastern Nebraska and western Iowa was sparking those showers,
which will track across parts of eastern Nebraska and western
Iowa through the morning. Trailing surface front is forecast to
settle into central sections of eastern Nebraska and western Iowa
this afternoon as another shortwave and upper level jet streak
dives into the region. A good majority of synoptic- and meso-scale
model output suggests additional development near and south of
this front will occur this afternoon. Instability progs are
relatively tame, so severe is not a real concern, but isolated
thunderstorms are certainly possible. Expect activity to affect
the southern halves of eastern Nebraska and western Iowa early in
the afternoon, then shift south of the state borders early this
evening.

Upper flow will begin to shift from northwest orientation in the
Plains to shortwave ridging on Tuesday as deep trough over the
Great Lakes into the Southeast U.S. finally begins to shift east.
Meanwhile a potent shortwave crossing the Rockies should be
approaching the High Plains Tuesday afternoon, and tracking across
our area Tuesday night, leaving mainly zonal flow in the Plains
for Wednesday.

Increasing mid level flow will induce lowering pressures in the High
Plains on Tuesday, promoting stronger southerly low level winds and
rapid transport of moisture north. Associated instability increases
with strong daytime heating Tuesday will feed thunderstorms in the
High Plains during the afternoon, with that activity spreading east
into eastern Nebraska and southwest Iowa overnight as theta-e
advection continues on 50kt low level jet. While instability will
decrease overnight, 1000-1500 J/kg of MLCAPE is advertised by
ECMWF/GFS across northeast Nebraska where bulk shear near 40kt is
forecast. Thus some strong to potentially severe storms are possible
there through midnight or so.

Convection will likely linger through the morning on Wednesday as
shortwave slowly works to the east. Southwest low level jet near
40kt is forecast into the afternoon as well, suggesting continued
development on backside of system will maintain convection for
much of the day. By late in the day, focus for convection should
favor southeast Nebraska and southwest Iowa where surface front
will likely reside as storm outflows meet synoptically-driven
southerly flow. Where storms do maintain/fire Wednesday afternoon,
even the more conservative ECMWF says over 2500 J/kg MLCAPE will
be available to fuel potentially severe storms with large hail and
damaging winds.

.LONG TERM...(Wednesday night through Sunday)
Issued at 321 AM CDT Mon Jun 26 2017

Convection from Wednesday afternoon activity will linger into
Wednesday night, most likely affecting southeast Nebraska and
southwest Iowa. Forcing should be dwindling as shortwave tracks well
to the east and 850 flow decreases as it turns more westerly after
midnight.

However another round of potentially severe weather is expected
Thursday. Strong shortwave ejecting from upper low centered over
southern Saskatchewan is forecast to dive into the High Plains of
western Nebraska Thursday afternoon then rotate east through our
area overnight. Broad northward transport of higher theta-e air in
response to lowering pressures with approach of shortwave is
expected to drive Wednesday frontal boundary back north into
Nebraska and Iowa, offering focus for convective development. Upper
60s to near 70F dew points are suggested by ECMWF/GFS, yielding 3000
J/kg or more of MLCAPE. Increasing mid level flow will also
contribute to an increase in bulk shear to 40-50kt range. Certainly
will see a wind and hail threat if this pans out.

We should see a dry period Friday into Saturday behind this exiting
system. However Saskatchewan low/trough is forecast to settle into
the Northern Plains this weekend, maintaining cyclonic flow regime
over Mid America. Impulses rotating through this flow could spark
showers and thunderstorms beginning Saturday afternoon, with
somewhat better chances on Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1227 PM CDT Mon Jun 26 2017

Showers and possibly a thunderstorm will affect the KLNK TAF
through about 19z. Otherwise, VFR conditions at all TAF sites.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...DeWald



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