Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service North Platte NE
523 am CST Tuesday Mar 3 2015
Short term...(today and tonight)
issued at 306 am CST Tuesday Mar 3 2015
Today and tonight...the rap and other models indicate the snow band
across northern Nebraska will exit this forecast area this morning. Some light
snow would likely persist into the afternoon as the Arctic front
undercuts deep moisture in place leaving a growth zone for snow
above 850 mb.
There is no real change in the snowfall forecast except to say the
models came in a bit drier across the north but this may just be a
wobble in the model consensus. Given the robust moisture and decent
middle and low level frontogenesis...1 to 4 inches of snow would appear
The model consensus of the hrrr...rap...mosguide and namdng suggests
gusts to 45 miles per hour behind the Arctic front. The bulk of the snowfall
will be occurring ahead of these gusts. So the Winter Weather
Advisory appears to be right on track.
Widespread fog has developed ahead of the Arctic front. Surface low
pressure is causing the winds to back with dry air aloft promoting
fog development. Light freezing rain...freezing fog and freezing
drizzle should continue ahead of the Arctic front. A check on the
Highway cams indicates the Road surfaces have not yet crossed the
freezing mark and only the Chappell camera appeared to be collecting
ice on the lens. Weather conditions will be monitored closely for
signs of icing which would warrant a Freezing Rain Advisory this
morning ahead of the Arctic front.
Once the Arctic front crosses the forecast area around 15z the icing
threat should end.
Lows tonight fall into the single digits above and below zero. The
warmer readings across the south are the result of cloud cover and
lingering snow across the far south. Skies should clear across the
north and wind chill reading across Sheridan and Cherry counties
will be approaching or exceeding the minus 20 threshold for a Wind
Chill Advisory. Later forecasts can refine this element of the
Long term...(wednesday through monday)
issued at 306 am CST Tuesday Mar 3 2015
Temperatures are the main forecast challenge going in the
extended periods...as Arctic high pressure will be replaced by
downsloping warming westerly wind on Thursday. Thus...below average
temperatures are forecast for Wednesday...but
thereafter...conditions favor near or above normal temperatures.
Wednesday...another cold day anticipated as Arctic high pressure
reigns supreme. Highs in the teens and 20s are forecast with
apparent temperatures dangerously cold during the morning hours.
Most locations should see wind chills of minus ten or colder until
noon. Thereafter...the medium and long range models are showing
good agreement in that a sharp trough...which extends from eastern
Canada southwest to Baja California will split and progress east through late
week. This will leave a cut off low south of the Desert
Southwest...but allow the eastward expansion of an amplified upper
ridge across the western Continental U.S.. as the upper levels become less
amplified over the plains...the pattern would then favor a more
direct path from the Pacific...rather than the Arctic which has been
observed lately. At the surface...Arctic high pressure will build
east with the advancing trough...leaving behind a greater southwest
to westerly component of the lower tropospheric wind. The
downsloping trajectory will work in concert with rising heights and
the associated warm air advection to promote rising temperatures Thursday and
Friday. Most locations will see highs in the 40s by Thursday...with
50s anticipated for Friday. The models are highlighting the passage
of a weak shortwave and cold front on Saturday. This airmass has a
greater Pacific influence...thus temperatures only are forecast to
cool slightly. It should be noted however that the GFS has came in
cooler than previous forecasts...with cooler 850 mb temperatures
nearing minus 5 across much of the forecast area early Saturday
afternoon. We may be a bit optimistic on the current forecast
highs...will see in the coming days. Otherwise the wave arrives
will little fanfare...moisture profiles in the troposphere are
rather lacking...so will continue the dry forecast. Beyond
Saturday...a downsloping regime reigns once again allowing for
another warmup. The models advertise the ridge axis building east
toward the High Plains early next week...highs should respond by
warming into the upper 50s...possibly lower 60s.
Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 523 am CST Tuesday Mar 3 2015
IFR/local LIFR in snow...blowing snow and fog continue until
around 15z this morning and then improve to MVFR 15z-18z.
VFR/MVFR in low clouds are expected from 18z Onward.
North winds increase to 34025g40kt this morning and decrease
during the afternoon.
MVFR/IFR in snow and low ceilings may develop tonight along and south
of Interstate 80. Lowest flight conditions are expected south
toward the Kansas border where snow is more likely.
Winter Weather Advisory until noon CST /11 am MST/ today for