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Area forecast discussion 
National Weather Service North Platte NE
339 am CDT sun Aug 31 2014

Short term...(today and tonight)
issued at 339 am CDT sun Aug 31 2014

Messy setup for convective trends in the next 24 hours as several
weaker pv anomalies move out of the approaching upper trough. These
upper pv anomalies have helped to enhance low level convergence on
several boundaries across the Central Plains and when combined with
a decent low level jet which developed ahead of the main Lee surface trough...have
developed weak convection across the forecast area earlier this evening
and now moving out of the area. Infrared Sat pics indicating cloud tops
warming across Nebraska currently...though cooling just to the south
across northwest Kansas as a convective cluster moves east there where better
middle level lapse rates exist. Next more significant pv anomaly moving
across southern Idaho and helping to generate more thunderstorms and rain across southern Wyoming. As
the northern most pv anomaly across South Dakota continues to move northeastward today...the
mean surface trough position will remain across the central portion of
the forecast area as evidenced by light winds for the morning hours. The
aforementioned stronger pv anomaly will move the mean upper trough
axis to coincide with the surface trough and enhance low level
convergence by afternoon. Ahead of this...low level moisture will
remain pooled in the eastern half of the state...and a redevlopment of
the low level jet mainly east of the forecast area tonight.

As for sensible weather...showers with embedded thunderstorms and rain will progress
into the eastern Panhandle this morning and into the sandhills during
the afternoon. Additional thunderstorms and rain expected to develop along the
developing front by middle afternoon...though coverage and intensity
remain uncertain in western Nebraska due to limited expected insolation due
to expected middle level cloud cover. Should the clouds break ahead of
the showers by afternoon...a quickly destabilizing atmosphere would
provide a better chance for strong thunderstorms and rain and with good deep layer
shear a few storms could reach severe limits...with large hail and
damaging winds the main severe weather threats. At this time believe
the best chance for this scenario to happen would be east of a line
from Stockville to Broken Bow to Ainsworth...similar to the current
Storm Prediction Center day1 outlook. Thunderstorms and rain should grow upscale after 02z or so...mainly
further east of the forecast area and have limited probability of precipitation after midnight
tonight to the northeastern most area.

High temperatures will also be dependent on cloud cover today and will
likely be held down the greatest in portions of the northeast

Long term...(monday through saturday)
issued at 339 am CDT sun Aug 31 2014

12z Monday and beyond. Zonal to slightly northwesterly flow aloft
will usher another pv anomaly across the northern plains Monday
afternoon and evening...bringing a chance for showers and storms
to our northern counties. The models are progging a weakly
unstable atmosphere by late afternoon...but bulk shear values
increase to the 30-40 knots range when storm initiation is
anticipated...a strong storm or two is possible. This activity
will shift east into north central Nebraska late evening and early
on Tuesday...and for this will carry low end chance probability of precipitation across
our northeastern zones through 12z Tuesday. The GFS remains fairly
progressive...indicating that sufficient forcing for precipitation
will largely be east of the County Warning Area by 06z Tuesday...the forecast was
trended toward the slower solution prognosticated by the 31.00z NAM.

Zonal flow once again becomes established across the forecast area
on Tuesday as a Pacific northwest trough digs south into
Washington. This will provide for dry conditions through at least
late Thursday as no major atmospheric perturbations are prognosticated to
impact the region. On Thursday however the upper pattern backs to
southwesterly as the Pacific northwest trough advances along the US/Canadian
border toward central Saskatchewan. In response to the eastward
progression of the trough...surface low pressure will deepen across the
High Plains and be forced east with a cold front. With a strong low
level baroclinic zone in place...any disturbance would operate on
the front...potentially allowing for storms. Will leave the CR
allblend procedure forecast as is for now...which indicates slight
chance to chance storms over much of the forecast area beginning
late Thursday through the remainder of the extended.

Looking at temperatures this week and into the weekend...Post
frontal conditions on Monday will quickly give way to return flow
and solid warm air advection into midweek. Highs will generally be in the 70s
to lower 80s Monday...but warm several degrees both Tuesday and
Wednesday...such that highs on Wednesday should top out in the upper
80s to lower 90s for most locations. Thursday through Saturday
temperatures will be impacted by the passage of the aforementioned
strong late week cold front. Widespread highs in the middle 70s seem
plausible at this point in time. Concerning lows...upper 40s to
lower 50s will be possible once again Tuesday morning as surface high
pressure allows for clearing skies and weak wind. Low temperatures
are expected to warm several degrees through middle-week with low 60s
possible by Wednesday...but cool once again behind the late week
cold front with readings mainly in the 50s.


Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1239 am CDT sun Aug 31 2014

Isolated thunderstorms and rain developing behind outflow boundary from earlier
convection which is moving quickly eastward across the forecast area and
evident on radar. Most of the thunderstorms and rain is east of the kvtn area but
have included a tempo group there. Further south thunderstorms and rain may stay
north of klbf but uncertainty has prompted a thunderstorms in the vicinity group there as
rain showers lagging and may develop further with low level jet in place. Short
range models suggest this would pass the area by 09-10z or so but
a second outflow boundary droppping southeastward from western South Dakota may interact
and will have to monitor for this.

Later today...timing of the more significant front will be crucial
in understanding the potential for more significant thunderstorms and rain
development across the area. Front should clear kvtn area prior to
peak heating and therefore believe better potential for widespread
thunderstorms and rain will be in the klbf taf site area...though confidence on
coverage area this far west is lacking based on short range model


Lbf watches/warnings/advisories...


Short term...jws
long term...Jacobs

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