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Area forecast discussion 
National Weather Service North Platte NE
614 am CST Wednesday Jan 28 2015

issued at 356 am CST Wednesday Jan 28 2015

500 mb analysis this morning had a large trough of low
pressure extending from New England southward into the western Atlantic.
Across the central Continental U.S....a ridge of high pressure extended from
Texas into the western Dakotas. West of this feature...a strong
shortwave trough was noted over southwestern Idaho. Current WV imagery has
the southwestern Idaho shortwave now over far northern Utah...entering southwestern
Wyoming. At the surface...a frontal boundary extended across eastern
Nebraska southward into the Ozarks. West of this feature...light westerly
winds were present...while east of this feature...winds were from
the south or south southeast. As of 3 am CST...skies were mostly
clear in the central and eastern County Warning Area...with increasing middle and high
clouds noted across the far western County Warning Area. Readings as of 3 am CST
ranged from 26 at North Platte to 45 at Ogallala.


Short term...(today and tonight)
issued at 356 am CST Wednesday Jan 28 2015

Winds...temperatures and the
threat for light precipitation in the northwest will be the main forecast
challenge today...followed by temperatures and winds tonight. For
today...low pressure will deepen across eastern South Dakota this
morning...tracking south along the frontal boundary into eastern
Nebraska this afternoon. At the same time...the upper level
disturbance...currently over southwestern Wyoming...will lift into the
Panhandle and north central Nebraska by 21z this afternoon. A decent
pressure gradient will develop behind the exiting low and east of
high pressure building into Montana. H850 winds this afternoon will
reach 30 to 40 kts across all of western and north central Nebraska.
By 21z...winds will be around 30 miles per hour with some gusts over 40 miles per hour as
efficient mixing takes place with decent cold air advection behind
the exiting front and unidirectional winds from h850 to the surface.
With good mixing and 850 mb temperatures in the high single digits today...highs
will reach the upper 50s and lower 60s. For highs...generally
followed the warmer mav guidance...which has verified nicely the
last couple of days. In addition to winds and temperatures...there
will be a small threat for precipitation in the west later this
afternoon in association with the appg shortwave. At this time...will keep
probability of precipitation fairly low as the best lift and weak instability will be west
of the forecast area along the front ranges of Colorado and southeastern
Wyoming. As the showers lift east...they will encounter drier air in
the lower levels...thus the low probability of precipitation. For tonight...a strong cold
front will track across the forecast area with a reinforcing shot of
gusty northwesterly winds and much colder air. By 12z Thursday...850 mb
temperatures will range from -7c in the -2c in the
southwest. With breezy conds forecast into the overnight...lows will
bottom out in the 20s. At this time...decided to leave a dry forecast in
place...even in light of a secondary shortwave trough which
approaches northern Nebraska overnight. The latest NAM solution is
indicating some flurries with this feature...with the GFS forecast being
dry. Will give a heads up to the oncoming shift and have them watch
the model trends today for tonights forecast.

Long term...(thursday through tuesday)
issued at 356 am CST Wednesday Jan 28 2015

A hybrid of Pacific and Arctic air will spill south through the
plains behind Wednesday night/S cold frontal passage. H850 mb
temperatures of -3c west to -10c farther east will ensure for a
chilly day. Breezy conditions to start the day...will gradually give
way to less wind through the day as the pressure gradient relaxes
and winds aloft decrease. Pacific air spreads east across the region
Thursday night into Friday. Have raised lows a few degrees Thursday a weak southwesterly low level jet develops. A bit of
this wind will mix to the surface in the favored areas of north
central Nebraska and the sandhills...helping to keep low
temperatures up a bit. Expect a mainly sunny day with mild
conditions Friday with the Pacific airmass in place.

Interesting set up Friday night through Saturday night. A large
plumb of sub tropical moisture...originating off the West Coast of
Mexico...will be drawn northward into the southern and possibly
Central Plains ahead of an upper level trough that will move into
the Desert Southwest/western Continental U.S. By Friday evening. At the same
time...a northern stream shortwave will be moving into British
Columbia from the Gulf of Alaska. The question is how will the
western Continental U.S. Trough...northern stream shortwave...and sub tropical
moisture all interact. The key to answering that question appears to
be in the northern stream energy. The timing of this energy diving
southeast into the central and northern plains will determine if
snow develops or not. If the energy is quicker than models are
currently forecasting...then the moisture needed for snow
development will likely be shunted off to the east. Currently all
model solutions...the Gem...GFS...and European model (ecmwf)...are such that the
timing of the northern stream shortwave is slow enough for the
moisture to move north into the region ahead of the feature. This
allows for snow to develop within region of middle level frontogenesis
associated with the northern stream wave. This frontogenesis and
associated snow band develops from west to east across Nebraska late
Friday night and continues through much of the day Saturday. Once
the northern stream shortwave slides through Saturday night...the
snow will rapidly come to an end as downglide quickly develops. Will
nudge the going chances for snow up a bit for Saturday into Saturday models agree this evening on the slower northern stream
energy coming into play. Will continue to monitor this the next few
model runs...and see if the slower wetter/snowier model solutions
continue for the area.

More certain will be the colder weather that will be introduced back
to the area as the northern stream energy passes. As surface low
pressure develops across Kansas Saturday...moving east into the
Mississippi Valley region Sunday...expect a batch of Arctic air to
be drawn south into the central and northern plains on the backside
of the low pressure system later Saturday through Monday. Then the
upper flow becomes more zonal Tuesday...with a milder Pacific
airmass moving back into the region.


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 609 am CST Wednesday Jan 28 2015

Strong northwesterly winds will develop later this morning and
will gust up to 30 kts this afternoon and evening. Clouds will be
on the increase this morning with ceilings drooping down to 10000 feet
above ground level at the klbf terminal this evening. Ceilings will drop down to 2500
feet above ground level overnight at the kvtn terminal.


Lbf watches/warnings/advisories...


short term...clb
long term...Taylor

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