Area forecast discussion...update 
National Weather Service Pendleton or 
922 PM PST Tuesday Jan 27 2015 

Updated aviation discussion 

Update...patchy fog and low stratus has redeveloped this evening 
in the lower Columbia Basin below 1400 feet mean sea level and the Yakima 
Valley. The lowest visibility was noted to be in upper Columbia 
Basin of central to northern Washington state but will keep on 
locations further south in case fog becomes more dense. 
Otherwise...have nudged overnight low temperatures a little higher 
as middle and upper level clouds has slowed radiational cooling this 
evening. A short wave trough and an upper level low passing to the 
southeast will bring mostly cloudy conditions and a slight chance 
of precipitation to the Cascades during the day on Wednesday. Bieda 

Aviation...06z tafs...a combination of an upper level low southeast 
of taf sites and a passing weak weather system has broken up low fog 
and stratus deck except at kpsc and kykm. A passing shower is 
possible as the weak system passes over through 29/00z at kdls and 
kalw. Decreasing temperatures above the inversion layer should help 
keep fog away from all other taf sites not presently affected through 
29/03z...but fog and stratus may start to reform at kalw and kpdt 
after 29/03z while conditions worsen once more at kykm and kpsc as 
brief subsidence occurs between weather systems. Another weather 
disturbance will approach central Washington and bring a vicinity shower to 
kykm after 29/03z. Bieda 


Previous disc... /issued 340 PM PST Tuesday Jan 27 2015/ 

Short term...tonight through Friday...high pressure will gradually 
weaken tonight through Wednesday as two systems collide across the 
Pacific northwest. Do not anticipate much in precipitation...except 
a slight chance along the east slopes of the Cascades and the 
southern Blue Mountains this evening. The cold air aloft with this 
system will weaken the inversion that has been in place across the 
lower elevations. This should help lift the fog into a status 
deck...and may even clear out some areas temporarily. Expect partly 
to mostly cloudy skies Wednesday with some clearing and fog 
redevelopment Wednesday night as high pressure rebuilds for the 
remainder of the short term. The most favored areas for fog on 
Thursday and Friday look to be along the foothills of the Blue 
Mountains...central and north central Oregon. Patchy fog is 
expected for the lower elevations. Otherwise...mostly dry 
conditions expected Thursday and Friday. Weber 

Long term...Friday night through Tuesday night...the long term 
period starts off with an upper level ridge over the Pacific northwest...which 
will allow patchy fog/freezing fog to form in the basins Friday 
night through Saturday night/Sunday. Heading into the Sunday through 
Tuesday period we are expecting a much more active weather pattern 
as the upper level ridge begins to break down. Model guidance is in 
good agreement that several disturbances will move through the 
region...bringing chances of rain and mountain snow. At this time 
snow levels are generally forecast to remain between 3000 to 5000 
feet with these storm systems...perhaps lowering to 1500-2500 feet 
Tuesday night in some locations. South to southwest winds will 
increase Sunday night into Monday...up into the 10-20 miles per hour range as a 
surface low passes near or just to the north of our County Warning Area. Dropped 
temperatures back several degrees in the Monday/Tuesday timeframe to 
account for the potential of colder air aloft. The 27/12z European model (ecmwf) is 
indicating 850mb temperatures dropping to between 0 to -4 degrees 
celsius during this time. In general expect near to slightly above 
average temperatures through the long term period. 77 


Preliminary point temps/pops... 
PDT 38 49 34 44 / 10 10 10 10 
alw 36 46 35 44 / 10 10 10 10 
psc 36 47 35 44 / 10 0 10 10 
ykm 31 44 32 42 / 10 10 10 10 
hri 36 49 35 45 / 10 10 10 10 
eln 40 45 33 43 / 10 10 20 10 
rdm 34 57 33 49 / 10 10 10 10 
lgd 38 51 32 47 / 10 10 10 10 
gcd 36 53 34 52 / 10 10 10 10 
dls 40 51 39 49 / 20 20 10 10 


PDT watches/warnings/advisories... 

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