Area forecast discussion...update 
National Weather Service Pendleton or 
1038 am PDT Wednesday Apr 23 2014 

Updated for aviation discussion 

Update...the latest radar was showing scattered showers over the 
Blue Mountains and over the Washington/or Cascades. Elsewhere isolated 
showers were occurring and this is expected for the remainder of the 
day. A storm system will take aim on the pacnw tonight with 
increasing showers expected toward Thursday morning. 

Otherwise temperatures will be slightly below normal and the present 
short term forecast appears on track. 


Aviation...18z tafs...a weak disturbance and a moist westerly flow 
will give the area broken to overcast skies today with a chance of 
mostly light rain showers. VFR condition will be prevalent...though 
the heavier showers may deteriorate to MVFR levels briefly. This 
evening a system will arrive and push a warm front into the area 
after 00z with more widespread rain and somewhat lower ceilings. 
This will continue overnight tonight and into the morning hours. 
Have kept ceilings at VFR levels but MVFR/IFR chances will be greater 
with this system than this afternoon. Winds have increased around 
10 to 20 kts with gusts to 30 kts and should drop to around 15 kts 
after 03z this evening. Weber 


Previous disc... /issued 500 am PDT Wednesday Apr 23 2014/ 

Short through Thursday evening...a weak disturbance 
will move east across the region this morning causing varying 
chances of showers. The best chances will be over and near the 
mountains, especially in upslope and slop over favored areas. An 
onshore low level flow will continue the chances of showers, though 
probabilities will be slightly lower than this morning. A stronger 
system will approach the Pacific northwest this evening. This system 
will swing a warm front across the region overnight through middle 
morning Thursday. As such will continue current high chances of 
precipitation for late tonight into Thursday morning. Will indicate 
Post-frontal lower probability of precipitation in the Lee of the Cascades Thursday morning 
due to downslope affects. This warm front will cause snow levels to 
rise tonight into Thursday. This stronger system's cold front is 
expected to move across the region Thursday afternoon and evening. 
Expect showers to accompany this cold front. May also see a few 
thunderstorms develop along this boundary late afternoon into early 
evening over the Blue Mountains and their adjacent foothills, the 
Grande Ronde Valley, as well as Grant and Wallowa counties. Breezy 
to locally windy conditions will be possible across the area both 
today and Thursday. 90 

Long term...Thursday night through Wednesday...a system will be 
moving out of the area Thursday night. Lingering instability should 
lead to a chance of rain showers over most of the area though the 
Washington Columbia Basin will be mainly dry west of the Tri-Cities. 
The instability will lead to a chance of a few thunderstorms in the 
early evening over the eastern mountains. Friday will see a trough 
remaining over the area and once again most of the area will have a 
chance of rain showers and mountains snow showers above 4000 feet 
through the day though the Washington Columbia Basin will only have 
a slight chance of rain showers. The trough will remain Friday night 
and Saturday though most of the energy will sink far to our south. 
This will allow the lower elevations to dry out while the mountains 
maintain a chance of rain and snow showers with the snow level at 
4000 to 4500 feet. The trough leaves to the east Saturday night as 
another system approaches the coast. Models differ as to the 
strength and timing of when it moves through the area. Have kept the 
current forecast of a slight chance of rain in the lower elevations 
and a chance of rain in the mountains Saturday night and Sunday then 
drying out in the lower elevations Sunday night and Monday. Ridging 
builds over the area Monday through Monday night with a weak system 
riding over the ridge and perhaps brushing the Washington Cascade 
crest with a slight chance of rain showers. Models diverge at this 
point with the European model (ecmwf) maintaining a ridge through Wednesday for more 
dry weather while the GFS pushes the ridge off to the east and sends 
a system through the area Tuesday night and Wednesday. Have leaned 
towards the European model (ecmwf) and have a dry forecast through Thursday. Perry 


Preliminary point temps/pops... 
PDT 56 45 61 41 / 50 60 70 60 
alw 57 48 61 44 / 60 60 80 60 
psc 62 49 66 47 / 30 60 60 20 
ykm 59 43 62 38 / 20 50 50 20 
hri 59 47 65 44 / 30 60 60 40 
eln 57 41 60 36 / 20 50 60 20 
rdm 56 38 58 32 / 30 60 50 60 
lgd 55 44 56 38 / 50 70 80 70 
gcd 55 39 57 36 / 40 60 80 70 
dls 59 46 63 42 / 50 70 60 40 


PDT watches/warnings/advisories... 

Threat index 
today : green 
Thursday : green 
Friday : 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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