Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
826 PM MST Sat Nov 22 2014
Discussion...numerous snow showers from the west central
mountains through the western Magic Valley are associated with
lift and moisture with a fast moving upper level trough. May get a
quick inch or two on grassy areas across the west Magic Valley
since temperatures are near 32f...snow showers there will
decrease to scattered for twin/Jerome by 11 PM MST. Moderate northwest
flow aloft will be moist enough for upslope showers to continue
across the NE Oregon mountains and higher terrain of Owyhee/Twin Falls
counties through Sunday morning and central Idaho mountains beyond Sunday
evening. Post cold frontal gusty winds across the Magic Valley
around 25 miles per hour at times tonight and Sunday morning are associated
with building high pressure 2-4 mb/3hrs across SW Idaho through
early Sunday morning. This feature may be strong enough to bring
northwest winds to 10 miles per hour to Ontario towards 11 PM but snow cover did not
entirely go away...surface winds are forecast less than 10 miles per hour
through Sunday...so boundary layer winds from the GFS are
preferred overnight as they capture the 35mph over Twin Falls and
calm to 10 miles per hour over the Weiser basin and lower Treasure valley.
Previous. No updates.
Aviation....expect scattered MVFR and local LIFR conditions in snow
in the ktwf/kjer area until about 06z. The mountains of Baker County
Oregon and central Idaho including kmyl will see scattered MVFR/IFR
snow showers through Sunday morning...becoming widespread after 18z.
Patchy valley fog is possible kboi-kono 06z-18z. Otherwise expect
VFR conditions through Sunday. Surface winds...west to northwest 5-
15 kts except 15-20 kts in the kbke and ktwf/kjer areas until
about 06z. Winds aloft...northwest up to 30 kts at 10k feet mean sea level.
short term...tonight through Monday...a cold front has moved
through the area today...helping to scour away most of the
inversion that has plagued the Treasure valley...and many other
smaller valleys...the past week or so. We feel weak inversion
conditions will continue tonight through Monday in the extreme
lower Treasure valley and have adjusted our forecast accordingly.
A moderate short wave will move through the area late this
afternoon through tonight... bringing additional showers to most
of the area. Snow levels this evening range from 4500 feet in the
south to 3500 feet in the north. Overnight the snow level will
drop to a range of 3400 feet in the south to 2700 feet in the
north. Winds will remain moderate in the western Magic Valley this
evening. Fog is likely in sheltered mountain valleys tonight...along
with the usual areas near McCall... Baker City...and in the
extreme lower Treasure valley. With moderate northwest flow aloft and
weak ridging tomorrow...showers will be mainly confined to the
mountains of SW Idaho and northern Baker County. Temperatures will be near normal.
Showers will continue in the mountains Sunday night before tapering off
Monday. The valleys will be dry Sunday night and Monday. Temperatures on
Monday will be a few degrees cooler than Sunday...resulting in
readings a few degrees below normal.
Long term...Monday night through Saturday...upper ridge builds
along the West Coast through Wednesday which will keep moist
northwesterly flow and precipitation focused over the central
mountains of Idaho. Clouds and little to no snow cover throughout
much of the western Snake River Plain should provide at or
slightly above normal temperatures. The ridge moves inland late
Wednesday and by Friday the ridge axis is over the forecast area.
This is when the inversion will be the strongest but the valley
temperatures as well as fog/stratus development will depend
largely on snow cover. At the moment...the lower Treasure valley
stands the best chance for colder temperatures and inversion fog/stratus
but overall confidence in the inversion forecast remains low.
After Friday the ridge appears to weaken allowing Pacific moisture
to move back into the Pacific northwest.
previous short term...snow pellets
previous long term....js/wh