Scientific Forecaster Discussion
Area forecast discussion...updated aviation discussion
National Weather Service Pendleton or
930 am PST Sat Dec 27 2014
Short term...weather system moving into the Pacific northwest this
morning. Clouds have overspread the forecast area and radar shows
precipitation is starting to increase in coverage especially over
western Washington. Strong northwesterly flow aloft will bring
significant snow to the Cascades and blues through Sunday morning.
Elsewhere lighter amounts of rain or snow are likely. A surface low
moving through the area combined with the flow aloft will increase
the winds today into tonight. Locally breezy southwest winds likely.
Temperatures today lower 30s to middle 40s. Precipitation will diminish Sunday
for a while then another colder system will move through Sunday
night into Monday with additional snow for most locations. 94
Previous disc... /issued 330 am PST Sat Dec 27 2014/
Short term...today through Sunday...a storm system moving southeast
along the British Columbia coast will move through the region today
and tonight. This system will bring precipitation to much of the area with
the heaviest amounts along the Cascade east slopes, over the Blue
Mountains, across the Grande Ronde Valley and in Wallowa County.
Snow levels in these areas will remain low, only rising to near 3200
feet in the Blue Mountains, briefly to near 3000 feet in the Grande
Ronde Valley and Wallowa County, and only to near 2500 feet along
the Washington Cascade east slopes. Snow levels in central Oregon
will rise to between 3000 and 3500 feet. These highest snow levels
will occur roughly from middle afternoon into middle evening. Overall
still expect decent snow fall in the areas where precipitation is heaviest
and over other higher terrain areas. Thus will continue the current
winter storm warnings and winter weather advisories. Colder air will
filter into the region late tonight and on Sunday. Thus snow levels
will fall late tonight. Daytime heating may lift the snow levels to
between 1500 and 2000 feet Sunday afternoon. Precipitation amounts will
tail off late tonight through the day Sunday and only expect light
amounts of additional snow. Winds will be locally breezy this
afternoon into tonight as the main surface low moves through
northern and northeastern Washington. 90
Long term...Sunday night through Saturday...another low will move
down from the north on Sunday night and Monday with much cooler air
and widespread showers. Snow levels will fall during this period to
near zero by Monday morning. Therefore...even the lowest elevations
could see some light snow accumulations. At this time 1 to 2 inches
of snow are forecast for the lower Columbia Basin and surrounding
valleys and foothills. A much colder and drier northerly flow will
then follow Tuesday through Thursday. The coldest day will be
Tuesday with daytime high temperatures only in the teens and 20s and
overnight lows in the single digits to below zero. Temperatures will
then very gradually warm Wednesday through Saturday. Models show the
Pacific Ridge weakening on Friday and a split flow developing with
moisture streaming both to the northeast and west of the local area.
This solution would keep the County Warning Area mostly dry...but have kept some low
precipitation chances in the forecast to account for uncertainty.
Saturday has better precipitation chances...especially over the
Washington Cascades and the northern blues. Although temperatures
may get into the middle 30s on Saturday...any precipitation will likely
fall as mostly snow. Cobb
Aviation...18z tafs...precipitation will continue to overspread the
area to all taf sites by afternoon with MVFR or even IFR ceiling
conditions in rain. There should be some breaks in the precipitation
late tonight with another round on Sunday. Snow showers may be
possible by Sunday morning at krdm and kbdn and a mix of rain and
snow at kpdt and kalw. Winds will become breezy this afternoon with
wind speeds mostly 10 to 20 kts. 93
Preliminary point temps/pops...
PDT 44 31 39 25 / 80 60 50 30
alw 45 34 38 26 / 80 80 40 30
psc 43 33 43 29 / 50 30 20 30
ykm 38 27 38 26 / 40 30 20 40
hri 44 34 43 30 / 60 30 20 30
eln 36 27 36 27 / 50 30 20 50
rdm 44 27 38 20 / 40 30 20 30
lgd 35 31 35 20 / 90 90 80 40
gcd 39 28 36 20 / 70 80 60 40
dls 47 35 45 31 / 60 40 30 40
or...Winter Weather Advisory until 10 am PST Sunday orz505-506.
Winter Storm Warning until 10 am PST Sunday orz049-050-502-503.
Winter Weather Advisory until 10 am PST Sunday orz509.
Washington...Winter Storm Warning until 10 am PST Sunday waz030.
Winter Storm Warning until 4 am PST Sunday waz520.
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