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Area forecast discussion...updated 
National Weather Service North Platte NE
1123 PM CDT Thursday Aug 21 2014

Short term...(this evening through friday)
issued at 300 PM CDT Thursday Aug 21 2014

Active Friday expected...as a strong shortwave disturbance lifts
northeast from Southern California toward the Central Plains.
Tonight will be fairly quiet ahead of the active day expected
Friday. Surface low pressure will slowly develop across eastern
Colorado overnight...in response to the approaching southern cal
shortwave. This will turn winds east overnight...with higher amounts
of low level moisture advecting westward into the area. Middle level
warm air advection gets underway late tonight...and a few elevated
showers/T-storms are possible after midnight across the
Panhandle.

Friday...expect an uptick in thunderstorm activity through the day.
Middle level warm air advection increases substantially by late morning
and afternoon as the shortwave trough draws near. Anticipate at
least a broken middle level clouds deck...as relative humidity and lift
increase in the middle levels of the atmosphere. Middle level instability
looks decent...and a scattering of elevated showers and
thunderstorms will be possible late morning and especially during
the afternoon hours. At the surface...a warm front will become
better defined during the afternoon...roughly along or just south of
the Interstate 80 corridor. Increasing surface based instability is
expected near the front...and surface based thunderstorms are
expected to initiate around 4 PM CDT or so. Deep layer shear
suggests some of the storms could become severe. While large hail is
possible with the severe storms...very heavy rain and precipitation
loading may favor more of a damaging wind threat. High temperatures
Friday could be a challenge...especially if more cloud cover occurs
than forecasted. But...with a warm tropical airmass in place...Don/T
think will have much problem reaching into the 80s. For now will
continue the middle to upper 80s at most locations.

Long term...(friday night through thursday)
issued at 300 PM CDT Thursday Aug 21 2014

Friday night will be busy across the County Warning Area as a closed area of low
pressure currently anchored in the Desert Southwest ejects
northeastward toward the Central Plains. At 00z Saturday a Lee side
surface low will be situated in eastern Colorado with a warm front
extending across the southern County Warning Area. Convection should already be
underway and moving into the County Warning Area from northeastern Colorado and
northwestern Kansas at the beginning of the period. These storms will be
moving through an environment favorable for severe
weather...characterized by steep middle level lapse rates and 30 to 40
kts of deep layer shear. The threat for severe weather peaks along
and north of the aforementioned warm front during the evening hours
as a southerly low level jet strengthens across western Kansas into southwest
Nebraska. A few supercells with large hail and damaging winds will
be possible. The overall threat for severe weather diminishes toward
the overnight hours...however a few strong to severe storm will
still be possible as a the low level jet promotes a strong warm air advection
regime and the development of elevated instability into central
Nebraska.

Heavy rain is also a threat Friday night as an anomalously moist air
mass will be in place over the Central Plains. An upper level surge
of monsoonal moisture over the top of a moist boundary layer will
push precipitable waters upwards of two Standard deviations above normal for late
August. Model blended quantitative precipitation forecast paints a swath of 1"+ over central
Nebraska ... east of a North Platte to Ainsworth line.
Locally higher amounts are likely with the most robust convection.
Fortunately storm motions will be on the order of 20 to 25 kts which
should help mitigate any widespread flooding concerns. The latest
NAM run changed tune and favored the eastern Panhandle for the
heaviest rain threat...however at this time it is an outlier and
contradicts the most likely scenario of the heaviest rainfall
following the veering low level jet through the night.

Lingering showers and storms are possible across the northern County Warning Area
Saturday morning...however conditions should dry out for
Saturday afternoon. Precipitation chances ramp up again Saturday night in
advance of another upper level shortwave. Currently have the highest
probability of precipitation in northwest Nebraska where thunderstorm development will be
aided by a southeastward advancing cold front. Have removed probability of precipitation
generally west of Highway 83 for Sunday as the cold front moves and
through and drier air advects into the Central Plains aloft.

Active pattern continues into next week as several shortwaves
translate through the larger scale trough slowly moving across the
northern rockies and into the northern plains. GFS and ec are in
poor agreement beyond Monday. Ec digs a trough southwest and
eventually cuts off a low as it builds a ridge into the Central
Plains. The GFS continues to slowly move the trough easterly across
the plains with daily thunderstorm chances. The poor consensus makes
forecast adjustments difficult...so did not make any changes to the
extended grids at this time.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1122 PM CDT Thursday Aug 21 2014

VFR is expected all areas through 18z. Thereafter...scattered
strong to severe storms develop across southwestern Nebraska and lift north
through the forecast area. Storm activity could still be ongoing
across northern Nebraska at 06z Friday night.

The area of showers across northestern Colo was showing lightning. This
has diminished. These showers are expected to move into western Nebraska
later tonight and perhaps persist Friday morning.

&&

Lbf watches/warnings/advisories...
none.
&&

$$

Short term...Taylor
long term...Martin
aviation...cdc

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