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Area forecast discussion
National Weather Service Pendleton or
1040 PM PDT Sat Apr 29 2017

Updated the aviation discussion

Update...the latest radar was showing an area of rain striking
the Cascades and some of the moisture was attempting to make it
across and into the interior portions of WA/OR. A weak disturbance
is forecast to track across the region overnight and the showers
should increase some across the entire area especially into the
WA/OR Blue Mountains overnight. Pops were adjusted some to reflect
this trend and minor changes were also performed to temps.
Meanwhile pressure gradients will tighten tomorrow and breezy
winds are expected with windy conditions in and near eln. Otherwise
the present short term forecast for tonight appears on track for

Aviation...VFR conditions will continue until a storm system brings
showers to the region and MVFR conditions may be approached at taf
site kdls after 08z and then the other taf sites after 10z.
Meanwhile wind gusts between 25 kts to 30 kts is possible at all taf
sites after 12z before diminishing after 02z and all taf sites will
remain VFR.


Previous discussion... /issued 300 PM PDT Sat Apr 29 2017/

Short term...tonight through Monday night...a ridge of high
pressure will remain offshore for the next couple of days though
there will be a couple of frontal systems riding over the ridge and
through the area. One will arrive tonight with a chance of light
rain mainly during the overnight hours. During the day tomorrow a
chance of rain showers will remain over the mountains while the
lower elevations dry out. Rain amounts will be just a few hundredths
of an inch with up to a tenth of an inch in the mountains. Snow
levels will be around 6000-6500 feet. Behind the front tomorrow,
pressure gradients will tighten up and heating will help mix down 30-
45 kt 850 mb winds to the surface. Most of the area will have 20-30
mph winds but the Kittitas Valley is expected to have 25-40 mph
winds with gusts to 50 mph. Have issued a Wind Advisory for that
zone from tomorrow morning through early evening. Winds will
decrease after Sundown. Sunday night and Monday morning will be a
break before the next system. Any precipitation will be confined to
the Washington Cascades. Monday afternoon another system will move
through the area with more light showers mainly over the mountains.
Precipitation amounts will be just a few hundredths of an inch. Snow
levels will be 4500-5500 feet. Not expecting any significant winds
with this system. Temperatures will be in the 60s with mainly 50s in
the mountains. Perry

Long term...Tuesday through Thursday night...a shortwave trough
will move east of the area Tuesday followed by a building upper
level ridge for Wednesday into early Thursday. The ridge will begin
to break down by Thursday evening. Expect fair conditions with
warming temperatures through the period. High temperatures within a
few degrees of 70 Tuesday in the lower elevations will warm to the
lower to mid 80s by Thursday afternoon. By late Thursday afternoon
and evening there will be at least a slight chance of showers and the ridge begins to break down and instability
increases. The activity will tend to form first near the Cascade
crest and then spread eastward during the evening and overnight
hours. 78

Friday morning through Sunday...forecast model solutions diverge
beyond Friday with depth and exact placement of longwave trough
across the northwest pac coast. The GFS has moved toward the European model (ecmwf) and
Canadian solutions but is still the weakest and least progressive
with this feature. Have leaned more toward the European model (ecmwf) solution for
now. There will be a slight chance of showers across the Blue
Mountains through Saturday evening as the trough and associated cold
front slowly shifts to the east. With the passage of the cold front
on Friday high temperatures will drop into the into the upper 60s in
the lower elevations for both Friday and Saturday. 74


Preliminary point temps/pops...
PDT 49 61 38 59 / 30 30 0 10
alw 52 65 43 62 / 40 40 0 10
psc 52 67 40 65 / 20 10 0 10
ykm 46 64 38 62 / 20 0 0 10
hri 50 65 39 63 / 20 10 0 10
eln 44 58 38 58 / 30 10 10 10
rdm 42 59 30 59 / 20 20 0 20
lgd 47 59 37 57 / 30 50 10 20
gcd 43 60 34 57 / 20 30 0 10
dls 50 61 42 62 / 30 20 0 20


PDT watches/warnings/advisories...
Washington...Wind Advisory from 7 am to 9 PM PDT Sunday for waz026.

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