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Area forecast discussion 
National Weather Service North Platte NE
352 am CDT Tuesday Oct 21 2014

issued at 352 am CDT Tuesday Oct 21 2014

The water vapor imagery loop at 0630z shows a plume of middle-
tropospheric moisture from central Texas northward along the
foothills of The Rockies and extending at least as far as
northeast Colorado. Aircraft wind reports show the trajectory
extending into eastern Alberta and western Saskatchewan. The GOES
derived total precipitable water and low-level radar wind
profilers show a trajectory of increased moisture from the
Southern Plains where 20-25mm is indicated. Hand analysis of the
07z mean sea level data showed a boundary from southeast Montana through
eastern Wyoming to northeast Colorado.


Short term...(today and tonight)
issued at 352 am CDT Tuesday Oct 21 2014

As the High Plains trough deepens...the increasing pressure gradient
will result in breezy to windy conditions by late morning to early
afternoon with south wind approaching 20 miles per hour sustained with gusts to
near 30 miles per hour. The wind will continue bringing moisture onto the High
Plains today.

As the surface boundary comes into western Nebraska is
likely to generate some frontogenetic forcing in the 305-310k
(800-650mb) layer first in the Panhandle around 09z and then toward
12z in central and north central Nebraska. The low level relative
humidity is high enough to warrant some mention of precipitation by
09z at least in the Nebraska Panhandle and northwest sandhills. The
low level humidity is lower in the eastern sandhills and other parts
of north central Nebraska until 12z or later. Blending the current
forecast with the precipitation output from the gemreg...the
nam12...the gfs40 and the European model (ecmwf) supports precipitation only in the
Panhandle and northern sandhills. Still...the forcing could support
at least some mention of a slight chance of rain after 06z north.
With 875mb based lifted indices of less than 0c...anything that does
develop will probably include thunder.

Long term...(wednesday through monday)
issued at 352 am CDT Tuesday Oct 21 2014

Forecast concerns through this period deal with
precipitation/thunder chances for Wednesday and then with
anomalous warm up for the remainder of the week.

Models are in good agreement through the majority of the period as
they have moved to a consensus solution for the evolvement of the
shortwave trough that moves across the forecast area Wednesday and
early Thursday. This leads to good agreement with the strong
ridging that builds in through the remainder of the week as all of
the longer term models have very similar progression of the
deepening longwave trough which moves from its current position
over Alaska and the Gulf of Alaska and then onto the Pacific coast
through the weekend.

The period begins with the upper level shortwave trough moving
into the northern and Central Plains from the west. At 12z the
surface cold front is just moving across the Nebraska Panhandle
and western sandhills. Although there is still some dry air in the
low levels /below 800mb/ the large scale lift is increasing...with
Omega signal of 5-10 ubar/S in the vicinity of the front. So would
expect showers and as forecast soundings are showing minimal
instability aloft can/T discount a few embedded thunderstorms. As
the system moves eastward through the day so will the showers and
thunderstorms as the moisture and lift pushes eastward. The
strongest Omega signal is seen in the late morning...then it
subsides early afternoon then strengthens again over central
Nebraska later in the afternoon. Was seeing reduced signals for
thunder during the morning hours...which pick back up in the
afternoon mainly across the eastern part of the forecast area as
some instability is able to build through the day. At this
point...with a signal of moisture transport into the western
sandhills and slight negative lifted indexes in the morning felt like
the mention of isolated thunder should be in the forecast.
Again...the frontogenesis/Omega/instability all increases along
the front in the afternoon and with moisture convergence in the
vicinity as well would expect an uptick of shower and thunderstorm
development. This may mostly occur west of the local forecast area
or just in the far eastern counties where the highest
precipitation chances continue.

Behind the front...strong subsidence and an abundance of dry air
push into Nebraska. This should bring a rapid end to any shower
activity Wednesday evening. Did hold on to slight chances beyond
midnight over the far northeast part of the forecast area but
think its looking more likely that the rain will have pushed out

Looking for Thursday through Saturday...the shortwave trough moves
east fairly quickly allowing the upper level ridge to strengthen
and build into the central part of the country. As mentioned
earlier...a strong longwave trough will be moving into the eastern
Pacific which will induce the good strengthening of the ridge.
Under the ridge anomalously warm air will be moving into the
region with closer to Summer like warmth expected for the Thursday
through Saturday time frame. Thursday/S highs look to be in the middle
to upper 70s as the warm air is starting to push in...but by
Friday and Saturday 850mb temperatures approach 20-21c over
Nebraska which would suggest highs up into the lower 80s for some
locations. With plentiful dry air in place to keep high amounts of
sunshine Don/T see anything prohibiting this from happening.
Also...just as a side note...looked at anomalies from the naefs
which showed 500mb temperatures on Saturday being of a return
interval of once every 10 years.

The upper level system over the Pacific moves onshore Saturday and
Sunday and there is some divergence in model solutions as it
moves over The Rockies with the European model (ecmwf) being the slower and deeper
trough solution. The main differences will be how much moisture
will be able to be pulled north into the forecast area prior to
the increased lift moving in as the system moves closer to the
local area. Either currently looks like there may be rain
chances for Sunday night and Monday...but the amounts will vary
depending on what solution plays out. Also...this system will
bring cooler and near normal temperatures to the area for the
first part of next week.


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1222 am CDT Tuesday Oct 21 2014

Strong low level jet of 30 to 40kts at 850mb expected across western
Nebraska through the early morning hours Tuesday. This will keep
boundary layer winds 10kts from the south over night especially in
northern Nebraska in the kvtn vicinity. Some MVFR ceilings may be
encountered over southwest Nebraska around sunrise but should remain
south of Interstate 80. Signal is not strong and have only mentioned
sct030 at klbf. Breezy middle morning and through the afternoon
especially over the Nebraska sandhills with south winds at 10 to
20kts with gusts to around 30kts. Visual flight rules over most of
western Nebraska Tuesday.


Lbf watches/warnings/advisories...


short term...Springer
long term...Brooks

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