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Area forecast discussion 
National Weather Service North Platte NE
345 am CDT Thursday Apr 17 2014

issued at 345 am CDT Thursday Apr 17 2014

The 07z water vapor imagery showed a baroclinic Leaf across
western Kansas and eastern Colorado to northeast New Mexico.
Darkening in the image indicated potential vorticity anomalies
over western South Dakota... northeast Iowa and north central New
Mexico. Analysis of the 07z mean sea level data showed low pressure centered
over northeast Iowa with a boundary or weak front stretched across
northeast Nebraska...southwest South Dakota and northern Wyoming.
High pressure was centered in southern Manitoba near Lake


Short term...(today and tonight)
issued at 345 am CDT Thursday Apr 17 2014

For today...return flow from the High Plains will generate
isentropic upglide over the weak boundary as indicated by the
moisture transport vectors in the 290-300k layer. With condensation
deficits of 45mb or lower...some precipitation is possible this
morning in northern Nebraska. A cross-section of Theta-E...relative
humidity and ageostrophic vertical circulation indicates some
instability in the 290-305k layer until around 18z. Therefore...
some mention of showers would be appropriate...though the coverage
is likely to be limited. Until the boundary layer temperatures get
above 0c in the 15-18z period...the showers will be light snow or a

As the boundary and surface low move out of the plains and into the
Ohio Valley...cloudiness will decrease and some sunshine can be
expected this afternoon.

Long term...(friday through wednesday)
issued at 345 am CDT Thursday Apr 17 2014

Starting on Friday...the upper level ridge will be building over
the plains while the two low pressure systems aloft now over the
Pacific Ocean move onland. The northern system moves into the
Pacific northwest...while the second pushes into Southern
California. Through the day Friday these systems will move east
slightly...with low pressure developing on the Lee side of The
Rockies. Several surface los will develop...but the one with the
most impact locally will be the one over eastern Wyoming/western
South Dakota. The frontal boundary associated with this will
extend all the way down into New Mexico. A warm front will lift
through the forecast area early in the day and as the pressure
gradient tightens looking for a rather breezy and warm day Friday.
The models have trended warmer on Friday...with 850mb temperatures
rising to around 20c over the western half of the forecast area.
Forecast soundings indicated mixing over the western areas up to
700-600mb and to 800mb over the eastern half. With adiabatic lapse
rates...this would suggest highs in the middle 70s to near 80 across
the west. Did warm temperatures 3-5 degrees across the forecast
area...but may need to go warmer yet as the forecast remains below
the previously mentioned highs from the soundings. As for the
winds...gradient winds look to be 20 to 25kts for much of the area
Friday afternoon...and winds in the mixed layer top out between 30
and 40 kts. At this time no fire danger is anticipated as enough
moisture is brought north to keep very dry air from taking relative humidity now is only dropping to 20 to 30
percent over parts of the Panhandle.

The cold front starts to make its way east Friday night...and
although cooler air moves in the temperatures shouldn/T drop too
far due winds staying breezy through the night. There is a
question of rain chances for Friday and Friday night. There is air
being lifted over the local area through this time...but moisture
is extremely limited and just Don/T think there is enough for
precipitation to develop. Held off on any mention of rain until
after midnight Friday...but even that is questionable as the layer
below 600mb is very dry. Didn/T want to eliminate precipitation
chances though as there are considerable differences in model
solutions through the early part of the weekend and confidence is
not high.

There will be chances for rain and thunderstorms Saturday and
Saturday night...but thunderstorms will depend on where the front
lies. 17.00z models suggest the front will be just to the southeast
of the forecast area so the higher chances for storms will not be
locally. Because of this...reduced mention of thunderstorms to
isolated and oncoming shift can re-evaluate.

This system moves east of the area by 12z Monday...with the flow aloft
briefly becoming fairly zonal. Then a large upper level trough
moves onto the West Coast Monday night to amplify the pattern a
bit more again. The models aren/T handling this system real well
as the past several runs from any model have waffled with the
strength and position of this system. For instance...the 17.00
runs are not near as deep with the base of the trough which
impacts the moisture flow north into the forecast area and the
development of a strong dry line with both having lesser impact
with the current runs. That being said...showers and thunderstorms
are still possible middle week but the trajectory right now would
bring the upper low over the central and northern plains which
could put the local area in the dry slot...leading to lower rain


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1238 am CDT Thursday Apr 17 2014

Ceilings in MVFR categories will continue over western Nebraska
through the early morning hours. Ceilings will improve into the VFR
categories after 17/12z. Middle and high clouds will move across
western Nebraska through the day on Thursday with winds increasing
out of the south southeast to 10 to 20 miles per hour with gusts into the low
20s. Could see a few sprinkles middle morning to late afternoon but not
confident that they will occur at taf sites and have left tafs dry
for now.


Lbf watches/warnings/advisories...


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