Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
316 am MST Friday Nov 28 2014
Short term...today through Sunday...SW flow aloft ahead of an
incoming cold short wave will continue the pattern of middle and
high level moisture streaming across the area today. Rain and snow
will increase in most areas today...especially in the north. The
snow level will be slowly falling today...but place like McCall...
where rain has been falling all morning...will not change over to
snow until late tonight. Temperatures will remain mild today...averaging
10 to 15 degrees above normal. Tonight...precipitation will continue in
most areas...especially the north...as snow levels gradually fall
in advance of the short wave. Saturday...a sharp cold front will
move through from northwest to southeast. This will enter Baker County in the
morning...reach the Boise area in the afternoon...and get to the
western Magic Valley by midnight. This will be a significant cold
front...with temperatures dropping sharply behind. Precipitation
will increase in the Snake River Valley Saturday...with most of
the precipitation falling as rain before the front moves through. There
may be a brief period of snow after the front passes...but frontal
passage should signal the end of the notable precipitation. Throughout
these first two days...precipitation in the mountains will be heavy.
Locations above around 7000 feet could see over a foot of snow.
Places like McCall...at 5000 feet...will see several inches of wet
heavy snow. At this time...it appears that Road temperatures will prevent
the snow from causing significant travel problems in the populated
areas...so no Snow Advisory will be issued. However...if you plan
on traveling over the higher passes...be prepared for heavy snow
and snow-packed roads through the weekend.
Saturday night the cold air will pour into the region behind the
departing cold front. There will be significant drying and precipitation
will decrease. On Sunday...the precipitation will taper off to showers...
and these will be found mainly in the south and east. Highs Sunday
will be 10 to 20 degrees colder than Saturday. Winds that will be
gusty Saturday night behind the cold front will diminish by Sunday
Long term...Sunday night through Thursday...warm front
associated with a moist Pacific low pressure system approaching
the California coast lifts north across the forecast area on
Monday. 00z GFS/06z NAM have the fastest timing of the frontal
passage...reaching McCall/Baker City around 18z Monday. 00z European model (ecmwf)
is about 6 hours slower. All guidance suggests the cold air will
mix out of most of the Treasure valley by the afternoon with
increased southeasterly winds. The warm frontal passage will
initially be dry as it moves northward through the dry Arctic
airmass. Moisture will increase along the front as the upper low
reaches the California coast and moisture is advected northeastward.
There is uncertainty regarding timing of the returning Pacific
moisture so have left probability of precipitation higher across much of the County Warning Area Monday.
The County Warning Area remains in the warm sector of the Pacific low off the California
coast through early Wednesday which will bring periods of
widespread precipitation. The low weakens as it moves inland late
Wednesday leaving moist westerly flow over the intermountain west.
Temperatures...below normal on Monday...will warm quickly and
remain above or near normal Tuesday through Thursday.
Aviation...mostly VFR conditions with middle-high clouds today. MVFR
conditions and mountain obscuration in the west central mountains
from rain and snow showers through early afternoon. Rain will
push south this afternoon...mainly north of a kbno-kono-ksnt
line...for MVFR conditions. Surface winds generally light. Winds
aloft near 10k feet mean sea level...west at 35 to 45 kts.
Weekend outlook...Saturday...an Arctic front will push south for
MVFR rain changing to IFR snow in the mountains. Otherwise expect
VFR conditions for most of southeast Oregon and southwest Idaho.
Saturday afternoon valley rain and mountain snow will spread south
to the Nevada line and continue across the entire area through late
Saturday night...with snow levels lowering to the valley floors.
Sunday drier air moving down from the north will bring improving
conditions...with mainly VFR.
Short term...snow pellets