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Area forecast discussion...updated 
National Weather Service Pendleton or
1014 am PDT Tuesday Sep 23 2014

Updated aviation discussion

Short term...morning update...a moist southwest upper level flow
will continue over the region through tonight. A wave continues to
move north-northeast off the Washington coast. This wave will spread
varying amounts of showers into the Washington Cascade east slopes,
and the Kittitas and Yakima valleys. The Oregon Cascade east slopes
should also see isolated to scattered showers at times. Lingering
isolated showers over the Blue Mountains, Grande Ronde Valley and
Wallowa County will continue to diminish in coverage through the
day. Weak warm air advection aloft should cause a few sprinkles of
rain from central Oregon north to the Simcoe Highlands, and over the
Lower Basin and Blue Mountain foothills of Washington this
afternoon. A slow moving cold front will move into western Oregon
and Washington tonight. Thus still expect increasing chances of rain
over the Cascade east slopes, central and north-central Oregon, the
Columbia River gorge, and the Kittitas and Yakima valleys. Updates
this morning focused on adjusting locations of showers and adding
sprinkles to the above mentioned areas. 90

Long term...previous active weather pattern is in
store for the forecast period but confidence in how the region will
be affected is low to moderate. Latest model guidance shows
continued differences between the dgex...GFS...and European model (ecmwf) concerning
the location of a longwave trough with associated moisture over the
Pacific northwest on Friday. The European model (ecmwf) is the most aggressive of the
three with an upper level low centered over southwest Oregon and
precipitation over the majority of the County Warning Area. The GFS and dgex are
drier with either no upper level low or differences in location of
the moisture axis. All three show reasonable confidence that the
east slopes of the Cascades...central Oregon and northeast Oregon
will have a decent chance of precipitation. The three solutions
diverge on confidence from the Oregon/Washington state border and
points northward...therefore have opted to keep slight chance for
this area. On Saturday...the European model (ecmwf) has an upper low moving across
southern Oregon while the dgex and GFS portrays this low further
south over central Nevada. As all models agree that precipitation
chances should decrease gradually from west to east...have opted to
reduce chances of precipitation in south central Washington...
central Oregon and the lower Columbia Basin while keeping slight
chance probability of precipitation along the higher elevations of northeast Oregon.

For Sunday through Tuesday...the model solutions diverge
considerably with moisture advection portrayed in the European model (ecmwf) along
with another upper low moving into the region by Tuesday. This would
support chances of precipitation areawide. The GFS and the dgex do
not portray as much moisture and keeps the region under
northwesterly flow. Seeing as the latter two models have
consistently maintained this portrayal and ensemble guidance
supports this solution...have opted to portray slight chance showers
along the east slopes of the Cascades and northwestward facing
slopes for the rest of the forecast period.


Aviation...18z tafs...a weak trough will hang up over the Cascades
producing occasional light rain kykm...krdm and kbdn...mainly after
23/21z. Remaining taf sites could see some sprinkles. Middle level
clouds will dominate with occasional MVFR ceilings during periods of
heavier rain krdm and kbdn. Winds will be generally less than 10
kts. Earle


Preliminary point temps/pops...
PDT 80 59 75 55 / 10 10 20 30
alw 80 63 77 59 / 10 10 20 20
psc 82 60 76 57 / 10 10 20 30
ykm 75 58 67 53 / 20 30 50 40
hri 81 58 75 55 / 10 10 20 30
eln 75 57 68 53 / 30 40 60 40
rdm 77 51 68 47 / 10 20 40 50
lgd 81 53 80 50 / 20 10 10 20
gcd 82 53 79 49 / 10 10 10 20
dls 76 60 70 57 / 20 40 60 50


PDT watches/warnings/advisories...

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