Ice Storm Warning 2, NWS Pendleton, OR

Area Forecast Discussion
National Weather Service Pendleton OR
320 AM PST Tue Jan 17 2017

.SHORT TERM...Today through Wednesday...A complex weather scenario
is leading to a tricky forecast for the next 36 hours. A Pacific
weather system is riding over a ridge and flattening it. Radar shows
showers reaching the Washington Cascade Crest already. An advance
initial wave will move through the northern portion of the area this
morning with the main thrust of precipitation in the afternoon and
tonight. This system is warm aloft, but the question is how fast
will the cold air at the surface be scoured out allowing
temperatures to warm above freezing. Believe it will take longer
than model guidance suggests as it usually too fast in doing so.
This means much of the northern half of the area will have a
freezing rain and sleet event through most of tonight before
temperatures finally warm up. Temperatures today will remain in the
mid to upper 20s in the Columbia Basin and adjacent valleys along
with the Columbia Gorge and east of the Blue Mountains. The rest of
the area, including Central Oregon will rise to the lower to mid 30s
this afternoon and have mainly snow and rain. Precipitation will be
just a few hundredths of an inch today. This evening precipitation
will start to increase with around a tenth of an inch in the lower
elevations and up to a quarter inch in the cascades. Overnight
precipitation will increase to 1 to 2 tenths of an inch in the lower
elevations with up to a half inch in the mountains. Not all of this
will be freezing rain as there will also be sleet and temperatures
will warm through the night and at some point will switch over to
rain. Will likely upgrade the current watches to winter weather
advisories but for the Columbia Gorge and perhaps the Washington
Basin am thinking to raise it to an ice storm warning but am still
working out details. Overnight lows tonight will be in the lower to
mid 30s in Central and North Central Oregon and in the 20s in the
rest of the area. However, if southerly 15 to 20 mph winds pick up
in the Blue Mountain foothills then temperatures should rise and
precipitation could turn to rain by late in the evening. Southerly
winds will continue on Wednesday and that will raise temperatures to
the upper 30s to mid 40s and end the freezing rain. A possible
exception is the Columbia Gorge which is sheltered from south winds
and will be the last to warm up. The current wind advisory in the
Grande Ronde Valley looks good and no changes will be made. Perry

.LONG TERM...Wednesday night through Monday.  Wednesday night
starts off with a good chance of rain as the upper low moves north
along the west coast of Washington with a trough of low pressure
reaching the coast by Thursday morning.  This trough will cross the
region Thursday and Thursday night and with the westerly flow will
look for decreasing precipitation chances across the lower basin
areas. The weather pattern remains active through weekend and into
early next week as a couple of low pressure system moves north along
the coast with several bands of moisture to move through during the
weekend and into Monday.  Snow levels will be high( 4500-5000 feet)
Wednesday night and remain around 3000-3500 feet through Friday
before cooler air pushes them back down near 1500-2000 feet through
the weekend.  93

&&

.AVIATION...12z Tafs. IFR/MVFR conditions with stratus and fog
will persist at KPSC, KPDT and KALW through 18z.  A narrow band of
moisture is expected to be near KDLS at 14z and them move eastward
through the morning reaching near KYKM by 17z and through KPDT/KALW
and KPSC at 18z. Precip with this band will be light, but should be
in the form of sleet or freezing rain across the Columbia Basin.
Steadier precip will spread across the region late in this period.
All sites are expected to see freezing rain, except KRDM and KBDN
where rain is most likely and continue overnight. 93

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  26  27  44  34 /  20  90 100  90
ALW  28  29  44  37 /  20  90 100 100
PSC  26  23  42  33 /  20  90  80  70
YKM  27  21  39  27 /  40  90  80  60
HRI  26  24  42  33 /  20  90  90  70
ELN  27  23  37  26 /  50  90  80  60
RDM  36  30  43  29 /  20  70  70  60
LGD  29  25  39  30 /  10  90  90  90
GCD  32  30  42  30 /  10  90  90  70
DLS  31  32  43  33 /  50  90  90  70

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 10 AM PST this morning for ORZ041-
     044-050-505-507-508-510-511.

     Winter Storm Watch from 10 AM PST this morning through Wednesday
     morning for ORZ041-044-507-508-510.

     Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Wednesday for ORZ050.

     Winter Weather Advisory from 4 PM this afternoon to 4 AM PST
     Wednesday for ORZ049.

     Wind Advisory until 4 AM PST Thursday for ORZ049.

WA...Air Stagnation Advisory until 10 AM PST this morning for WAZ024-
     026>029-521.

     Winter Storm Watch from 10 AM PST this morning through Wednesday
     morning for WAZ024-028-029.

     Winter Weather Advisory until 4 AM PST Wednesday for WAZ026-027.

     Winter Weather Advisory until 8 PM PST this evening for WAZ520.

     Winter Weather Advisory until 8 PM PST this evening for WAZ521.

&&

83/93/93