672 
FXUS66 KPDT 021558
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
758 AM PST Wed Jan 2 2019

.UPDATE...A ridge of high pressure has continued to dominate the
areas weather with dry conditions but will slowly push to the east
allowing for a disturbance to approach the two state area later
today. The disturbance will spread mid and high level clouds to
the region and snow showers are expected to develop along the wa
cascades this afternoon. The challenge overnight will be with the
timing of the warm air advection that is expected by Thursday 
morning. Otherwise minor changes were done to temps and sky cover
and now the present short term forecast appears on track while
afternoon highs climb into the upper 30s to lower 40s with 30s in
the mountains.

&&

.PREV DISCUSSION... /issued 309 AM PST Wed Jan 2 2019/ 

SHORT TERM...Today through Friday...An upper ridge over the area
is beginning to flatten as a weather system approaches the Pacific
Northwest. The area will have increasing cloudiness today though
any precipitation will be light and confined to the Washington 
Cascade crest. The system will be riding over the ridge and only 
making slow progress tonight. The warm front of the system will 
bring a chance of light rain as far east as Ellensburg by early 
Thursday morning then across the Washington portion of the area on
Thursday. The big concern will be freezing rain in the Kittitas 
and Yakima valleys Thursday morning. Snow levels will be rising 
to 5000 to 6000 feet, so precipitation below that elevation will 
be rain. However, in the Yakima and Kittitas Valleys, temperatures
will be below freezing for at least part of the morning and this 
will lead to rain freezing to surfaces. Precipitation amounts will
just be a few hundredths of an inch and should melt in the 
afternoon. Will hold off on any winter weather highlights there 
for now as confidence isn't quite there and amounts will be 
lighter than the usual criteria. Winds will increase and become 
breezy in the mountains and especially the Grande Ronde Valley 
Thursday and will remain so through Friday. Thursday night the 
warm front will lift north out of the area and the cold front of 
the system will begin to cross the Cascades. A chance of rain and 
snow will be confined mainly to the mountains with snow levels 
starting out at around 5000 feet Thursday and falling to around 
3500 feet over most of the area Friday though the Blue Mountains 
eastward will have snow levels around 3500 feet. Most of the area 
will just see a few hundredths of an inch though the Cascades will
have up to a third of an inch Thursday night and around a tenth 
of an inch on Friday. Temperatures today will be in the 30s though
Central Oregon will reach the lower to mid 40s. Friday and 
Saturday will be in the mid to upper 40s with mid 30s to lower 40s
in the mountains. Perry

LONG TERM...Friday night through Wednesday...Any lingering mountain 
snow showers become increasingly sparse through the evening Friday. 
Saturday and Sunday the area will be under the influence of an upper 
low in northern California, opening to a wave over much of the 
Pacific Northwest. Under westerly flow the lower elevations will be 
largely rain shadowed and with minimal moisture support any snow 
accumulations in the mountains will be rather limited. Colder air in 
the upper Treasure valley along with increasing winds aloft will 
support some enhanced winds in the Grande Ronde Valley and Blue 
Mountains foothills through the weekend, but don't think these will 
reach advisory criteria. Will see some better potential for 
widespread precipitation, possibly significant precipitation in the 
mountains Monday into Tuesday as fetch of Pacific Moisture noses in 
from the south as a warm front spread north over the region. With 
strong warm air advection snow levels will be rising rapidly from 
around 1500 feet through 5000 feet. Surface wind fields do suggest 
some cold air damming against the Washington Cascades, so could see 
snow lingering long enough to warrant some winter highlights over 
the east slopes. May also see a switchover the freezing rain prior 
to becoming all rain, but too early to get a good feel for exactly 
how the thermal profiles will evolve. Both thermal gradients from 
the upper Treasure valley to the Columbia Basin and winds aloft will 
be stronger than on the weekend and would expect some more 
significant gusts, possibly nearing warning criteria in the Grande 
Ronde Valley and Blue Mountain foothills Monday into Tuesday 
morning. May also see some stronger winds aloft mixing to the 
surface off the higher terrain via mountain wave action in central 
Oregon. The cold front associated with this system passes through 
Wednesday with precipitation becoming confined to the mountains once 
again along with a brief uptick in winds region wide with cold 
frontal passage. Peck

AVIATION...12Z TAFs...Some local reductions in visibility 
in mist will be possible near YKM/PSC this morning along the rivers, 
but do not think visibility will drop below VFR at the terminals.
Will start to see mid/upper level cloudiness return late this 
morning as the ridge begins shifting off to the east in advance of
the next system Thursday. May see some downslope winds developing
off the Blues this evening with some gustiness at ALW by Thursday
morning. Winds remain light at the remaining terminals. Peck

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  40  31  46  36 /   0   0  10  10 
ALW  40  32  48  37 /   0   0  20  20 
PSC  36  31  45  37 /   0  10  20  10 
YKM  39  31  42  33 /   0  10  30  40 
HRI  38  31  45  35 /   0   0  10  10 
ELN  39  29  40  32 /  10  20  50  50 
RDM  45  28  49  34 /   0   0  10  10 
LGD  35  28  34  32 /   0   0  20  10 
GCD  36  25  42  32 /   0   0  10   0 
DLS  41  33  44  36 /   0  10  30  50 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 4 PM PST this afternoon for ORZ041-
     505-506-509>511.

WA...None.
&&

$$

97/