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Area forecast discussion 
National Weather Service Pendleton or
711 PM PST Wednesday Jan 28 2015

Update...main concern tonight will be widespread low clouds and/or
fog in the lower Columbia Basin and adjacent valleys and north
central Oregon. The fog has spread into the Oregon Blue Mountain
foothills during the past couple of hours...but it has lifted some
into a stratus layer. Dense fog advisories are in effect for these
foggy areas until 11 am Thursday. An upper level ridge is weakening
as a wave moves into it tonight. This may bring a few light rain
showers to the Cascade east slopes...otherwise there will just be
some middle and high clouds associated with the disturbance. High
pressure aloft will rebuild over the region Thursday night through
Sunday with mostly dry conditions. However there will remain fog and
low clouds across the same areas that have it now due to a lack of
mixing of the lower atmosphere. Temperatures will be near normal in
foggy areas and well above normal in sunny areas. 88


Aviation...06z tafs...IFR or MVFR conditions are expected until 19z
Thursday for kalw...kpsc...kykm...kdls and possibly at kpdt due to
fog and low clouds. Krdm and kbdn should be VFR with just some middle
and high clouds. After 19z conditions will improve temporarily and
then will worsen again Thursday evening. Winds will remain light and
variable at all taf sites through the next 24 hours. 88


Previous disc... /issued 351 PM PST Wednesday Jan 28 2015/

Short term...tonight through Saturday...high pressure will remain
in place over the area for the next few days. A weak disturbance
will slide along the Cascades tonight and may generate a few light
rain and snow showers along the Washington Cascade crest but amounts
will be barely measurable. In the lower elevations, low stratus and
fog continues over the Columbia Basin, the Yakima Valley and the
Washington portion of the Blue Mountain foothills. While some areas
have shown improvement in the fog this afternoon, have extended the
dense fog advisory through tomorrow morning as I anticipate that the
fog will return this evening and overnight. Also expect that patchy
fog will move into the Kittitas Valley, north central Oregon as far
south as Madras and into the rest of the Blue Mountain foothills.
Tomorrow through Saturday will be a quiet period with no systems
crossing over the ridge. Above 2500 to 3000 feet it should be partly
cloudy with continued above normal temperatures in the 40s and lower
50s. Below that elevation, low clouds and patchy fog will continue.
Possibly the fog will be dense but will let later shifts evaluate
those conditions. Temperatures under the stratus will reach about 40
in the day time and drop to around freezing at night. Winds will
remain light through the period. Perry

Long term...Saturday night through Wednesday upper
level ridge will be established over much of the Pacific northwest for Saturday
night into Sunday. Therefore a strong inversion will be in place
with patchy fog and freezing fog in the forecast for the lower
basins. By Sunday afternoon and Sunday night most guidance is in
agreement that the upper ridge will begin to break down as a
disturbance moves into the region from the Pacific. Continued with
chance probability of precipitation for lower elevation rain through Monday morning...with
chance to low end likely probability of precipitation for rain/snow in the mountains. At
this time snow levels are forecast to vary between 2500 to 4500 feet
north-central and 4500 to 6000 feet south during the Sunday
night/Monday period. Left lingering slight chance to low end chance
probability of precipitation of light rain in the lower elevations and rain/snow in the
mountains for Monday night into Tuesday with the moist westerly flow
continues. By Tuesday night into Wednesday there is more uncertainty
in the forecast as the 12z European model (ecmwf) tries to bring another moisture
laden system into the area while the 12z GFS amplifies a ridge over
the region with a dry northwesterly flow. Went with a general model
blend for now for this period...which gave slight chance of rain for
the lower elevations and lower end chances of rain/snow for the
mountains. Temperatures start of near to slightly below average with
the fog in the lower basins for Saturday night and Sunday...but then
warm to above average levels for the Monday through Wednesday period
with the warmer westerly flow in place. 77


Preliminary point temps/pops...
PDT 33 40 32 40 / 0 10 0 0
alw 34 40 34 40 / 0 10 0 0
psc 33 42 32 41 / 0 10 0 0
ykm 30 38 30 40 / 10 10 0 0
hri 33 40 33 41 / 10 10 0 0
eln 32 42 31 40 / 10 10 0 0
rdm 31 48 30 48 / 10 10 0 0
lgd 31 45 29 46 / 10 10 0 0
gcd 33 51 31 49 / 10 10 0 0
dls 39 47 36 43 / 10 10 0 0


PDT watches/warnings/advisories...
or...dense fog advisory until 11 am PST Thursday orz044.

Washington...dense fog advisory until 11 am PST Thursday waz027-028.

Dense fog advisory until 11 am PST Thursday waz029.


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