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fxus66 kpdt 221758 aaa 
afdpdt 


Area forecast discussion...updated 
National Weather Service Pendleton or 
1058 am PDT Thursday may 22 2008 


Updated aviation 


Update...water vapor satellite shows an upper level low over Utah 
spreading middle and high clouds eastward over eastern Washington and 
Oregon. The visual satellite shows more of a northeast to south 
movement. Showers have decreased on radar...but expect increase 
again this afternoon as a weak vorticity maximum moves through northeast 
Oregon this afternoon and evening. Overall pop coverage looks 
good..but may tweak sky cover for higher cloud coverage over the 
eastern Columbia Basin. Winds are lighter than forecast in 
places...but mixing of higher winds aloft will increase during the 
day and believe higher winds will be more representative of overall 
conditions. Coonfield 


&& 


Aviation...expect VFR conditions through the evening hours. Ceilings 
will become a little more uncertain as moist easterly flow begins 
backing up against the Cascades. Have reasonable confidence around 
sunrise that ceilings at kdls and krdm will be at or below MVFR minimums 
and less so at kykm. Also, flow and precipitation descending off the 
Blue Mountains will probably bring ceilings down toward MVFR minimums as 
well for kpdt and more so at kalw. In general, expect shower 
activity to become more stratiform in nature towards tomorrow 
morning. Jbonk 


&& 


Previous discussion... /issued 440 am PDT Thursday may 22 2008/ 


Short term...today through Friday night. An elongated trough 
currently resides over the western half of Continental U.S....and a closed low 
has developed over the Great Basin. Moisture rotating around the 
low...enhanced by low level convergence...is bringing scattered 
showers along the Blue Mountains and the Blue Mountain foothills. 
Elsewhere...skies are partly to mostly cloudy. The main challenge 
in the forecast for today will be locating the individual 
disturbances that may bring additional showers. The best potential 
for showers will remain over the eastern mountains models show a piece 
of energy moving across NE Oregon and southeast Washington this afternoon. 
The GFS is stronger with this disturbance than the NAM. Because the 
GFS has done a decent job the past few days and there were moderate 
showers over The Blues yesterday...will continue the scattered probability of precipitation 
for the Blue Mountains eastward. A stronger wave will arrive tonight and 
deepen into a secondary low as it moves across eastern Oregon Friday 
and Friday night. Models have consistently shown high quantitative precipitation forecast for our 
eastern zones. Will keep likely to categorical probability of precipitation and high quantitative precipitation forecast 
amounts tonight and Friday across the John Day basin and ochoco 
Highlands and the NE mountains...grande ronde and Wallowa valleys. 
Even the Blue Mountain foothills could see around 0.3 of an inch of 
rain in 24 hours. Snow levels tonight through Friday night will be 
around 6000-6500 feet. The high elevations such as The Eagle cap 
wilderness and the Strawberry mountains will likely see significant 
snow this late in the season. Snow levels will be too high to 
warrant a Snow Advisory. Instead...will issue a Special Weather 
Statement to alert hikers and campers who plan to head out this 
Memorial Day weekend. Johnson 


Long term...Saturday through Thursday...a large and persistent 
upper low pressure system will linger over the western USA for the 
first part of the extended period. Wrap around moisture from this 
low will bring numerous rain showers...with snow showers possibly on 
the highest peaks this weekend. The medium to long range models are 
in fairly good agreement with the placement and strength of the low 
pressure system. There will also be enough instability to support a 
slight chance of thunderstorms in the afternoon and evenings across 
the southern and eastern portions of the forecast area for both 
Saturday and Sunday. The closed low will weaken and open up to a 
trough by Monday or Tuesday...but will still keep isolated to 
scattered showers over the region...which will persist through the 
remainder of the long term forecast period. Temperatures will begin 
cooler than normal...but will gradually transition to a warming 
trend on Sunday and Monday. Temperature readings will climb back 
into the upper 70s to middle 80s in the lower elevations...and 60s to 
lower 70s over the mountains by Monday as the flow becomes more 
southerly on the eastern side of the trough as it retrogrades 
westward...keeping the warmer side of the trough over the forecast 
area. 88 




&& 


Preliminary point temps/pops... 
PDT 65 48 62 48 / 30 30 70 30 
alw 66 48 65 49 / 20 30 60 30 
psc 71 52 68 51 / 10 20 30 20 
ykm 69 49 68 48 / 10 10 30 20 
hri 68 48 66 49 / 20 20 40 20 
eln 67 47 67 47 / 10 20 30 20 
rdm 58 38 57 38 / 10 30 50 30 
lgd 57 46 56 45 / 30 50 60 40 
gcd 58 42 55 42 / 30 50 70 40 
dls 65 51 65 50 / 10 20 40 30 


&& 


PDT watches/warnings/advisories... 
or...none. 
Washington...none. 
&& 


$$ 


Ti:ggg 
for additional weather information, check our web site at... 
www.Weather.Gov/Pendleton 
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