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Area forecast discussion 
National Weather Service North Platte NE
347 am CST sun Mar 1 2015

issued at 347 am CST sun Mar 1 2015

At 09z...surface high pressure extended from the New England
states...Midwest...into the northern plains. Skies were mostly
cloudy across western Nebraska. Weak radar returns indicated from
portions of the Panhandle into the western sandhills. With the
exception of Pine Ridge reporting 3sm -sn ovc035...ceilings across
western nebr are relatively high at 8k-10k feet above ground level...with flurries

Temperatures holding from 15 to 20 above beneath the cloudiness.
Winds were light and variable.


Short term...(today and tonight)
issued at 347 am CST sun Mar 1 2015

For today...the Arctic airmass impacting western Nebraska the past
few days will loose its tight grip. Temperatures at 850 mb will
moderate to -4c at iml and -9c at onl. Mixing down these
temperatures to bring highs near 35 at onl...36 at iml and bbw to 32
at Gordon. These highs slightly warmer than a 50/50 met/mav guidance
blend. If fact the latest rap13 and hrrr in close agreement on highs
and were used as a basis for forecast highs. Expecting clearing
skies from north to south today..with the nctrl becoming mostly
sunny by late morning...with southwestern nebr becoming partly cloudy in the
afternoon. Winds to become northwest today at 5 to 15 miles per hour nctrl and 5 to
10 miles per hour south.

For tonight...a positively tilted trough across Nevada into southern
calif. Downstream of this upper trough...a band of 125kt winds at 300 mb
will extend from southern calif...across Utah...northern Colorado...and Nebraska.
Western Nebraska will be in southwesterly flow aloft. Warm air advection at 700 mb will advance
from eastern Colorado into southwestern nebr overnight. A slight chance for snow is
supported across southwestern nebr by the models...especially the 00z
NAM...00z Gem and 03z sref. Lows tonight mostly to range from the
middle teens nctrl to the upper teen to near 20 southwest.

Long term...(monday through saturday)
issued at 347 am CST sun Mar 1 2015

12z Monday and beyond. The primary focus of the extended remains
centered on precipitation chances beginning late Monday
evening...potentially lasting into the afternoon hours on Tuesday.

The Middle Range models continue to advertise a solution in which a
northern stream shortwave trough will amplify southeastward across
the Canadian prairies and northern plains late Monday night into
Tuesday while additional shortwave energy rotates northeast from the
desert SW toward the Central Plains. As the northern stream trough
amplifies...a strong Arctic front will dive south across the High
Plains and adjacent American prairies...reaching northwest Nebraska
during the pre-dawn hours Tuesday. The medium range models are at
odds with the timing of the front thereafter. The 01.00z European model (ecmwf)
seems to be a good comprise at this point as the 00z NAM is on the
slower side of the forecast envelope...and the GFS remains very
progressive. Regardless...the current forecast calls for early
highs Tuesday morning for much of the forecast area...with a
non-diurnal trend into the afternoon and evening hours as the front
should be through the County Warning Area by midday. Despite the timing issues with
the front...the models have a good handle on the quantitative precipitation forecast fields as all
seem to target the highest probability of precipitation across our northern zones. Moisture
advection is shown to be solid as a southerly low level flow
develops off the Gulf and arcs north into the Central High plains on
Monday. As heights fall with the approaching shortwave/S/...DPVA
will spread east across Nebraska and work on upglide targeting the
285-300k surfaces. Accumulating snow is expected. As of now...a
consensus of quantitative precipitation forecast would suggest upwards of a tenth to possibly two
tenths of an inch of quantitative precipitation forecast across our northern zones. It is in this
area where the ageostrophic response to a passing 150kt ulj would
promote frontogenetic banding and enhanced snow rates. Using the
higher end of the forecast quantitative precipitation forecast...would one expect accumulations of 1
to 3 inches across northern Nebraska...with possibly higher amounts
where the banded precipitation occurs /NW Nebraska./ For now...will up
probability of precipitation across our northern zones and continue to mention snow chances
in the severe weather potential statement...but begin to highlight possibly heavier amounts across
our northwest and northern zones. Further south across the central
sandhills and southwest Nebraska...snow chances are less will predominately keep probability of precipitation at chance or less for
now. One potential impact to the central and southeastern portions
of the forecast area Monday night is possibly a brief period of
freezing rain. The models all agree that middle level warm air advection ahead of the
shortwaves will be strong...with 800 mb temperatures shown to be in excess of
5c at klbf Monday evening. The NAM is leading the charge with the
freezing rain potential...however it is suspect as it is deemed too cold at the
surface. Strong southerly ll warm air advection and mixing should help keep above
0c into the pre-dawn hours across the eastern third of the forecast area. So
for freezing rain was placed in the forecast...but we will need to
continue to monitor. Will go with rain or snow in these areas.

Beyond Tuesday evening...the forecast generally calls for dry
conditions. Temperatures will be cold mid-week...but the long range
solutions all agree that a warming trend will take place over the
Central Plains. Rising heights and westerly downsloping low level
flow will help push highs back into the 40s and 50s by the end of
the work week.


Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1110 PM CST Sat Feb 28 2015

A few light snow showers...currently over northeast Colorado...
will make their way across southwest Nebraska. As they come
across...ceilings of 2000-3000 feet above ground level and visibility at or
above 5sm are likely...though very localized.


issued at 347 am CST sun Mar 1 2015

The 07z river gage readings indicated an ice jam continued on the
North Platte river near Lewellen upstream of Lake McConaughy with
the stage remaining slightly above the 7.5 foot flood stage. A
couple of sites on the main Stem of the Platte show ice jam signals
as well...though well below flood stage. Temperatures will warm to
near 35 at Lewellen today and 40 for Monday...but will probably not
be above freezing long enough to affect the ice. Highs only in the
low to middle 20s Tuesday and Wednesday and lows in the single digits
will likely cause ice jamming to persist or worsen slightly at
Lewellen and could develop in other river in western nebr. Significant
warming is forecast Thursday and beyond that will aid in breaking up
the ice jam. jams are rare going into March.


Lbf watches/warnings/advisories...


short term...roberg
long term...Jacobs

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