Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Pendleton or
733 PM PDT Friday Apr 18 2014

Short term...satellite shows cirrus increasing over the region this
evening ahead of the next approaching weather system. Expect partly
cloudy skies overnight. Even with the cloud cover temperatures will
be cold tonight as the airmass is fairly dry and surface dew points
are low. Most locations will be in the 30s. An upper level trough
will push a cold front through the area Saturday. Main impact will
be increased winds in the afternoon and evening. The Columbia Basin
into central Oregon will have breezy west winds. Precipitation
should be mostly over the Cascades and a little over The Blues.
Otherwise partly to mostly cloudy skies expected. 94


Previous disc... /issued 230 PM PDT Friday Apr 18 2014/

Short term...tonight through Monday night...weak ridge of high
pressure will build over the area today and tonight. Temperatures
will be in the lower to middle 60s today and upper 60s
tomorrow...before another cold front pushes through tomorrow
afternoon. Breezy winds and a chance of showers...mainly over the
mountains will accompany this frontal system. As this system exits
the area...brief high pressure will once again return Sunday
morning. Temperatures will be a bit cooler Sunday...but should
still be a nice day...with highs in the lower to middle 60s. By Monday
southwest flow will have set in and temperatures are expected to be
in the 70s across the lower elevations. Moisture will begin to
spread across the Cascades Monday afternoon ahead of the next cold
front. By Monday afternoon and evening precipitation chances will
increase across all areas. For now have not added thunder to the
forecast...but will not rule it out as a possibility. Expect the
cold front to push through late Monday...early Tuesday. Weber

Long term...Tuesday through Friday night...a negatively tilted
trough will be over forecast area on Tuesday with rain showers
likely over mountains and a good chance of showers at lower
elevations. Tuesday night the trough moves into Idaho/Montana for
decreasing probability of precipitation overnight. Wednesday high pressure begins building
into the region from the west for decreasing probability of precipitation at lower
elevations with a chance of showers in mountains through Wednesday
afternoon. Wednesday night through Thursday night mainly dry
conditions due to the ridge. Friday/Friday night moisture begins
increasing in higher terrain for a chance of showers over mountains.

Aviation...00z tafs...VFR will occur over the next 24 hours. The
ridge axis of an upper level ridge of high pressure offshore moves
east to the coast by early this evening. Sinking air associated with
the ridge will keep dry conditions in place east of the Cascades
throughout the forecast period. The ridge axis will move into
Idaho/Montana by daybreak Saturday, thus allowing winds aloft to
back from west to southwest by daybreak on Saturday morning.
Scattered high clouds will stream through the ridge today with cloud
bases around 20000-25000 feet above ground level and then lowering to middle levels this
evening with bases beginning around 15000-20000 feet this evening and
then lowering to 10000-15000 feet overnight into Saturday morning.
Saturday afternoon cloud bases will lower and thicken to broken
7000-11000 feet above ground level. Pressure gradients have weakened this afternoon.
As a result sustained winds will be 8-17 kts through sunset and then
early this evening become 6-12 kts for a few hours after sunset,
then become drainage winds of 4-8 kts by 05z/19th and persist
through overnight. Wind will increase late Saturday morning through
Saturday afternoon, becoming 14-20 kts by 20z/19th. Polan


Preliminary point temps/pops...
PDT 35 66 38 62 / 0 10 10 0
alw 39 67 43 62 / 0 10 10 0
psc 33 68 41 65 / 0 10 10 0
ykm 33 62 36 63 / 0 10 20 0
hri 32 67 39 65 / 0 10 10 0
eln 33 61 37 61 / 0 10 20 0
rdm 29 63 26 68 / 0 10 10 0
lgd 32 66 35 61 / 0 20 20 0
gcd 30 64 30 61 / 0 10 10 0
dls 36 65 41 65 / 0 20 20 0


PDT watches/warnings/advisories...

Threat index
Saturday : green
Sunday : green
Monday : green

Green: none or limited need for watches, warnings, or advisories.
Yellow: a few watches, warnings, or advisories possible or in effect.
Red: numerous watches, warnings, or advisories possible or in effect.

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