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Area forecast discussion...updated 
National Weather Service Pendleton or
955 am PST Wednesday Jan 28 2015

Updated aviation discussion

Update...a weak system is moving out of the area this morning.
Observations are not showing any precipitation so have removed all
mention today of a slight chance of rain and snow showers except
along portions of the Cascade crest. In the lower elevations, the
main concern is the low clouds and dense fog that developed in the
Oregon and Washington Columbia Basin zones and in the Kittitas
Valley overnight. Numerous locations have visibilities down to a
quarter mile or less, so the dense fog advisory looks good for now.
In the last hour or so, southwest winds have carried the fog from
Hermiston into Walla Walla. Have issued a Nowcast for the Walla
Walla area due to the dense fog. If I end up extending the dense fog
advisory past 11 am PST, may add the Washington Blue Mountain
foothills to the advisory. For now have adjusted the forecast as if
fog will improve this afternoon. Have lowered temperatures around
Walla Walla for today. Expect that the fog and low stratus will
strengthen and increase in coverage tonight to include all of the
Blue Mountain foothills, north central Oregon down to Madras and
into the kittias valley. Have also made some minor wind direction
adjustments through tonight. Forecast update already out. Perry


Aviation...18z tafs...LIFR/IFR conditions from fog/stratus are
currently affecting the kykm...kpsc..and kalw terminals with MVFR
ceilings at kdls. Expect the fog/stratus to remain in place for these
locations through at least this afternoon before some gradual
improvement is possible after 22z. Guidance is not handling the
current fog and low stratus very well...but visible satellite shows
widespread fog in the Columbia Basin and the Washington Blue
Mountain foothills below about 1200 feet in elevation. If the
west-north-west winds are persistent enough later today we may have
to watch for fog building into kpdt terminal after 21z...however at
this time I did not have enough confidence to include in the
forecast. Expect VFR conditions at kbdn and krdm through the taf
period...with just some VFR br at krdm after 29/09z. Winds will
remain or below 10kts at all sites over the next 24 hours. Murphy


Previous disc... /issued 300 am PST Wednesday Jan 28 2015/

Short through Friday...a weak system continues to
drift across the region early this morning. This system will cause a
few showers near the Cascade crest today, with a few showers in
Wallowa County this morning. Also a few sprinkles of flurries will
be possible over The Blues this morning. This system has mixed out
the low level inversions across most of our Oregon zones. The
inversions in over some of our Washington zones persist with some
areas of dense fog having formed early this morning. Also areas of
dense fog have redeveloped in the Lower Basin in Oregon. Thus will
issue dense fog advisories for the Lower Basin in Oregon and
Washington, and the Yakima Valley in Washington for much of this
morning. Another weak system is expected to bring a few showers to
south-central Washington tonight into Thursday morning. Otherwise
expect dry conditions due to increasing upper level high pressure.
This upper level high pressure will cause low level inversions to
increase across the interior northwest. Thus will continue to
indicate an increase in fog coverage over our area tonight through
Friday. High temperatures will continue to be warmer above the inversions,
though not quite as warm as in recent days due to some cooling
aloft. High and low temperatures within foggy areas will see limited
diurnal changes, with high temperatures in the 30s to low 40s. 90

Long term...Friday night through Tuesday...high pressure ridge
remains over forecast area beginning Friday night for dry conditions
persisting through Saturday night. Sunday a warm front associated
with warm air advection in the middle levels Ushers in a chance of rain
during the day on Sunday. Then a Pacific middle/upper level short wave
and associated dynamic lift moves into the Pacific northwest Sunday
night for rain likely, except for a chance of rain in Benton and
Franklin counties Sunday night. Monday the upper level short wave
moves across forecast area for a chance of basin/valley rain and a
chance of snow in the mountains with snow level 4500-5500 feet
through Monday afternoon. Monday night a weak disturbance moves
through southern Oregon for a chance of rain in central and north
central Oregon, the Blue Mountains and the east slopes of the
Cascades. A middle/upper level ridge of high pressure builds over the
region on Tuesday. Polan


Preliminary point temps/pops...
PDT 49 33 40 32 / 10 10 10 0
alw 43 35 43 34 / 10 10 10 0
psc 41 35 44 34 / 0 10 10 0
ykm 41 33 42 32 / 10 20 20 0
hri 42 34 44 34 / 0 10 10 0
eln 49 33 42 32 / 10 20 20 0
rdm 56 29 46 28 / 10 10 10 0
lgd 50 29 47 29 / 10 10 10 0
gcd 52 33 50 32 / 10 10 10 0
dls 50 39 46 36 / 10 20 10 0


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

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


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