Area forecast discussion...updated 
National Weather Service Pendleton or 
1109 am PDT Thursday Oct 30 2014 

Updated aviation discussion 

Update...a warm front was moving north across the region with an 
area of rain following it. The bulk of the precipitation is located across 
northern Oregon and southern Washington including the east slopes of the Washington 
Cascades. Most of the precipitation should continue moving north. By midday 
portions of the region should break into some sunshine and high 
temperatures should warm above normal. Therefore afternoon 
temperatures have been increased a few degrees and the present short 
term forecast appears on track for now. 


Aviation...18z tafs...a warm front moving north is still bringing 
light rain to kykm, which should end by 21z this afternoon. MVFR 
will continue at kykm and kalw until 20z-21z today, then improve to 
VFR. Otherwise, VFR conditions will prevail through this evening. 
Conditions deteriorate to VFR/IFR at kdls, kykm, krdm and kbdn 
overnight due the cold front bringing lowering ceilings with steady rain 
spreading east across region. Rain starts at kdls around 31st/01z, 
then at kykm by 04z, krdm and kbdn by 08z, kpsc and kpdt by 13z, and 
kalw by 14z. Winds at or below 10 kts are expected during the taf period. 


Previous discussion... /issued 420 am PDT Thursday Oct 30 2014/ 

Short through Saturday...a warm front associated with 
a developing weather system along the coast is moving northward 
across the forecast area this morning. Most of the precipitation 
with this front is over western areas from the Blue Mountains 
westward and northward. However did not rule out possible light rain 
over the Wallowa and Elkhorn Mountains. The warm front will be to 
the north of the County Warning Area by 00z this afternoon. After that a cold front 
will begin to push eastward with the winds switching to the 
southwest to northwest tonight. This will be a slow moving cold 
front with an upper level jet stream parallel to it. As a result 
there will be significant rainfall over and just to the east of the 
Cascades tonight and Friday. On Friday the front will make an 
advance to the east with the precipitation spreading into the lower 
Columbia Basin southward across central and north central Oregon. 
The cold front will continue to move eastward finally reaching the 
Idaho border by Friday evening (00z-06z saturday) with likely probability of precipitation 
moving into the Blue Mountains eastward late Friday afternoon and 
evening. At that time the low level flow will become southwest to 
northwest behind the cold front which will be downslope off the 
Cascades. This will cause rain shadowing over the Simcoe Highlands 
northward across the Yakima and Kittitas valleys with decreasing 
probability of precipitation there. Drying will continue overnight Friday into Saturday 
morning from west to east. Likely to categorical probability of precipitation will continue 
from the Blue Mountains eastward on Saturday. West of the Blue 
Mountains drying will take place with the rain ending over the lower 
Columbia Basin and central/north central Oregon as well as the 
Yakima/Kittitas valleys. The GFS model has the best handle on the 
timing of the cold front and leaned mostly to it for this forecast 
package. The air behind the cold front will be substantially cooler 
with snow levels dropping to around 4500 feet over western 
areas...causing the precipitation to change over to snow above this 
level in the Cascades before taping off. Since most of the 
precipitation will have moved east by that time any snow 
accumulations will be very light if any over the higher Cascades. 
Drying will continue from west to east in the early extended period. 
Winds will be light through the short term with the exception that 
they will increase over north central Oregon and the eastern 
Columbia River gorge Saturday afternoon due to mixing of higher 
winds aloft down to the surface behind the cold front. Temperatures 
will be above normal today by a few degrees...but cooling to near 
normal on Friday and then about 3 to 6 degrees below normal on 
Saturday. The most dramatic cooling will take place over the western 
County Warning Area on Friday and Saturday behind the slow moving cold front. 88 

Long term...Saturday night through Wednesday exiting 
upper level trough will result in a gradual decrease in 
precipitation chances across the lower Columbia Basin. Wraparound 
moisture and northerly flow behind the exiting system may keep rain 
below 3500 feet and snow above 3500 feet going through the day 
Sunday mainly over The Highlands of central to northeast Oregon. 
Another weather system will approach the region with an associated 
warm front that will move across the area Monday afternoon and 
evening. This will result gradually increasing chances of 
precipitation again with snow levels rising through the day Monday 
to about 6500 feet. The upper level shortwave trough will move 
across the region heading into Tuesday bringing at least a slight 
chance of rain with snow levels continuing to rise to about 7500 
feet given the subtropical moisture source. Model solutions diverge 
somewhat Tuesday night and Wednesday with some indications of drying 
from the GFS and the dgex...but the European model (ecmwf) brings another moisture 
laden shortwave trough to the region. Have opted to lower probability of precipitation some 
by blending climatology to the prior forecast. Temperatures during the 
period will be near normal Sunday...with gradual warming increasing 
the temperatures up to 10 degrees above normal by Wednesday. Bieda 


Preliminary point temps/pops... 
PDT 60 46 56 40 / 20 10 70 70 
alw 61 49 58 44 / 20 10 60 70 
psc 58 45 58 42 / 30 10 60 60 
ykm 56 42 55 36 / 80 70 70 20 
hri 59 43 57 40 / 30 10 60 60 
eln 55 43 52 36 / 90 80 70 20 
rdm 63 39 51 31 / 20 20 80 70 
lgd 62 44 58 39 / 20 10 50 70 
gcd 64 44 57 38 / 10 10 60 70 
dls 60 46 55 42 / 100 80 80 20 


PDT watches/warnings/advisories... 


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