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Area forecast discussion 
National Weather Service Pendleton or
924 PM PST sun Nov 23 2014

Short term...evening update...the region will remain under a
northwest upper level flow tonight through Monday. The wave that
brought showers to portions of the area today has moved east. As a
result shower activity has been diminishing across the area. A few
bands of light showers continue to cross the Cascade crest and
affect parts of the Cascade east slopes. This process will continue
through the night, but will gradually decrease and end towards
daybreak. Also a few bands continue over the interior mountains of
northeast Oregon. These too will gradually decrease and come to an
end overnight. Still expect a mostly dry day Monday, though the next
system imbedded within the northwest upper flow will begin to spread
precipitation into the Cascade East Slope zones during the afternoon. Snow
levels will fall to between 2000 and 3500 feet tonight, then rise
again Monday, ranging from 3500 feet in central Washington and 5000
feet in central Oregon by late afternoon. Locally breezy winds will
decrease overnight. Current forecast package generally in good shape
and only made adjustments based on latest trends. 90

Long term...previous discussion...a very busy extended as active
weather threatens the Holiday weekend. A ridge of high pressure will
continue to build over the area by middle week. Moisture is expected to
overrun just to the north of the County Warning Area...mainly affecting the Spokane
County warning area. Slight chance to chance precipitation will remain over the east
slopes of the Washington Cascades and the mountains of northeast
Oregon through Wednesday night. A strong cold front moving south
from Canada will flatten out the ridge of high pressure Thursday...
providing a moist westerly flow to the area for Thanksgiving. Right
now have not gone too aggressive with probability of precipitation on it is
expected to be all rain...and there may be a decent rainshadow
affect for the basin. So 20-30 percent probability of precipitation in the forecast for the
lower elevations with 30-50 percent for the mountains.

Warm southerly flow from the south looks to slow the arrival of the
Canadian cold front until late Friday night into Saturday. Saturday
Onward is where it gets interesting. These two air masses continue
to battle through the Holiday weekend...and there is still some
model discrepancy as to how much precipitation will fall across the
area...and the time it will fall. The current overall consensus
indicates that the cold air will reach about 50 miles south of the
I-84 corridor...and all areas to the north will see snow as the
general form of precipitation. Central Oregon and the John Day
Highlands is where it gets challenging. These areas could see a rain
snow mix...or possibly freezing rain. Have not introduced the
freezing rain to the forecast due to timing and uncertainty. By
Sunday morning parts of north central Oregon and southern Washington
are expected to be below freezing and may have some snow
accumulations. Will continue to monitor the forecast and make
updated as changes occur.


Aviation...previous discussion...00z tafs...showers continue to
move across most taf sites this evening. Peak activity should be
through 06z...with some lingering showers at kalw and kpdt through
09z. Krdm...kbdn...and kykm may escape the showers due to
rainshadowing. Winds will be a bit breezy as well with wind speeds
10-15kts...gusting to 25kts at times. Ceilings tonight are in the potential for mist/fog increases. Have introduced
lowered ceilings/visible into the MVFR/IFR category at taf sites of concern.
Ceilings should start to improve after 18z and become scattered-broken 7-10kft.


Preliminary point temps/pops...
PDT 36 48 40 58 / 20 10 40 30
alw 37 48 42 60 / 20 10 40 40
psc 35 48 40 58 / 10 10 40 30
ykm 29 42 33 53 / 10 10 30 30
hri 36 49 40 58 / 10 10 40 30
eln 30 42 33 52 / 20 10 40 30
rdm 25 47 34 61 / 10 10 30 20
lgd 32 45 34 53 / 60 10 50 60
gcd 30 41 31 55 / 30 10 40 30
dls 38 51 40 54 / 20 10 40 40


PDT watches/warnings/advisories...

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