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Area forecast discussion 
National Weather Service Pendleton or
747 PM PDT Tuesday Apr 21 2015

Update...upper level trough and cold front moving into the
Pacific northwest this evening. Satellite showing significant
cloud development over northern California and southern Oregon.
This cloudiness will move northward across the forecast area for
the remainder of the evening and overnight. Had a few weak
thunderstorms earlier over central Oregon. Radar showing more
storms over northern California. Could still see a few storms for
the next several hours otherwise scattered showers likely this
evening and overnight. Strong pressure gradients moving into the
region with the front. Westerly winds are increasing and expect
breezy to locally windy conditions through Wednesday. Much cooler
tomorrow with good cold advection. High temperatures down about 10-15
degrees. 94

Previous discussion... /issued issued by National Weather Service Spokane Washington/

Short term...
tonight through Thursday...changes are coming during this period
as unusually warm upper level ridge will be replaced by a slow
moving upper level trough. As of 2pm...the trough was located just
off the coast with moisture streaming northward through northern
California and western Oregon. Models are in good agreement that
the trough axis will swing inland this evening. Initially this
will push cooler marine air east of the Cascades (as it has
already done through the Columbia gorge)resulting in a good wind
increase for most locations. It will also begin to trigger an
increasing chance of showers and even a evening thunderstorm.
Convection is beginning to fire over SW Oregon and is drifting
slowly to the north-northeast. These storms could impact The Bend
and Redmond area this evening before spreading east-northeast
overnight into NE Oregon and the Blue Mountains. By morning the
trough axis will shift east of the Cascades with most of the
moisture and lift spreading into extreme eastern Oregon and
Washington. The risk for precipitation elsewhere in the morning
will be small as much drier air move into the backside of the
trough. This drier air will continue to filter over the remainder
of the forecast area by afternoon with minimal risk of showers
except perhaps along the Idaho/or border. The main change with the
passing trough will be much cooler temperatures and windy
conditions. The windiest location as usual will be in the
Kittitas Valley. Wind speeds of 25-35 miles per hour will be possible with
gusts reaching 45 miles per hour. The current Wind Advisory looks good for
that area. Temperatures should be around 10-15 degrees cooler than
today which is still slightly above normal for this time of year.

For Wednesday night and Thursday the weather will turn dry and
less windy as shortwave ridging builds ahead of the next offshore
trough. Temperatures will rebound slightly with valley highs
generally in the 60s. Fx

Long term...
Thursday night through Tuesday...forecast models are in general
agreement of a closed low over southern British Columbia and
northern Washington Thursday night and Friday and then pulling east of
the region on Saturday. There are a couple of disturbances
associated with this low that will track across the region...but
the most numerous shower activity is expected well north of the
area closer to the cold pool aloft associated with the low.
Downslope westerly flow off the Cascade crest will limit shower
activity to isolated at best for the Columbia Basin and across
central Oregon...with isolated/scattered showers expected across
eastern Oregon and southeast Washington. Occasional breezy winds
can be expected in this pattern through the Kittitas Valley and
eastern Columbia River gorge as relatively cooler air from the
west side spills through the Cascade gaps.

After this a large closed low in the Gulf of Alaska will send a
moist frontal system into the area. Details however are uncertain
with the potential for some digging of this system which could
shunt most of the precipitation north of the area on Monday and Tuesday.
There also timing differences with the initial warm front with GFS
showing precipitation crossing the Cascades Saturday night...European model (ecmwf) on
Sunday...and the Gem Sunday night. All this said...confidence is
low in the details and kept a chance of rain in the forecast
Sunday through Tuesday with temperatures near to above normal. Jw

Aviation...
00z tafs...small clusters of showers and thunderstorms developing
in south central Oregon will be our primary concern through 03z.
The Bend and Redmond airports will experience showers and perhaps
a handful of lightning strikes before cooler more stable air
behind an advancing cold front cuts off the fuel for convection.
Remnants of these showers are expected to be entrained northward
overnight along a middle-level cold front bringing a good chance for
showers to Pendleton and Walla Walla. We will have to monitor the
timing of these showers expected primarily before sunrise. Gusty
west winds will impact most regional airports during the next 24
hours with the strongest gusts in the Lee of the Cascades and
through the Columbia River gorge. Localized gusts to 35 miles per hour or
more will be possible at wind prone sites like The Dalles and
Ellensburg. /Gkoch

&&

Preliminary point temps/pops...
PDT 47 60 34 63 / 20 20 0 10
alw 49 61 38 64 / 20 30 0 10
psc 48 67 38 67 / 10 10 0 10
ykm 47 64 37 64 / 10 10 0 10
hri 47 66 36 66 / 10 10 0 10
eln 46 60 38 62 / 10 10 0 10
rdm 39 60 25 61 / 40 10 0 10
lgd 46 59 32 60 / 20 30 0 10
gcd 42 61 32 62 / 50 40 0 10
dls 49 61 39 65 / 10 10 0 10

&&

PDT watches/warnings/advisories...
or...none.
Washington...Wind Advisory until 8 PM PDT Wednesday for waz026.

&&

For additional weather information, check our web site at...
www.Weather.Gov/Pendleton

$$

94/

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