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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Tuesday
• 
• High: 77 °
• Low: 55 °
• Chance of T-Storms

• Wednesday
• 
• High: 70 °
• Low: 50 °
• Chance of T-Storms

• Thursday
• 
• High: 70 °
• Low: 50 °
• Chance of Rain

• Friday
• 
• High: 72 °
• Low: 46 °
• Chance of Rain

• Saturday
• 
• High: 81 °
• Low: 54 °
• Partly Cloudy

Area forecast discussion 
National Weather Service Pendleton or 
755 PM PDT Monday Jun 17 2013 


Short term...tonight and Tuesday...low pressure system off the 
coast continues to trigger instability over the forecast area. For 
rest of tonight most of the convection will be across the west and 
northern portion of the forecast area. Expect some isolated 
thunderstorms to continue well into tonight so I added them in the 
evening update. So far most thunderstorms have just contained brief 
heavy rain and some gusty but some small hail is still possible. 


The low pressure system will move closer to the coast on Tuesday 
increasing the chance of thunderstorms across the forecast area as 
well as the potential for stronger storms. 


&& 


Previous discussion... /issued 534 PM PDT Monday Jun 17 2013/ 


Short term...tonight through Thursday. With upper low offshore and 
southerly flow over the region low level instability is increasing. 
Cumulus is developing mainly over the higher terrain. 18z NAM 
continues the trend of scattered showers and isolated thunderstorms 
developing late afternoon and continuing into the evening with 
possible showers through the overnight period as well. Cloud cover 
should keep low temperatures fairly mild with many locations staying 
in the 50s. The upper low moves closer to the coast on Tuesday. 
Expect another day of scattered showers and thunderstorms. With the 
jet overhead tomorrow any storms that develop have better potential 
to be stronger. Surface temperatures will be cooling as 850mb temperatures 
show a large decrease. Forecast will have highs about 10 degrees 
cooler than today. The low moves directly across the region Tuesday 
night and Wednesday. Models are generating some pretty good amounts 
of rain. Will continue with showers and thunderstorms however the 
potential for a good stratiform area of rain on the eastern side of 
the low exists. Additional airmass cooling plus cloud cover will 
bring high temperatures down into the 60s for most areas. Models differ on 
have fast the low will move off to the east Thursday with the GFS 
showing a much better chance of showers continuing through the day. 
Forecast will be a blend of the GFS and NAM with chance showers and 
continued cool temperatures. 94 


Long term...Thursday night through Monday...mid/upper level low 
over Pacific northwest Thursday night will keep a chance of showers 
over the Blue Mountains. Low continues over region on Friday with 
forecast area on southern flank of low, which imposes a northwest 
flow aloft and thus downslope winds with sinking air across lower 
elevations for dry conditions. However, there will be chance of 
showers over the Blue Mountains and east slopes in central 
Washington Cascades during the day on Friday. Friday night the low 
moves east into Idaho/Montana for a chance of showers in the evening 
on the Blue Mountains, but downslope winds and attendant sinking air 
elsewhere over the forecast area will yield dry conditions Friday 
night. Through the weekend a middle/upper level ridge of high pressure 
will produce sinking air and thus dry conditions for Saturday and 
Sunday. Monday a large middle/upper level trough in the Gulf of Alaska 
pushes a cold front into the region for increasing chance of showers 
mainly over the mountains. Included a slight chance of thunderstorms 
for Monday afternoon/evening. Polan 


Aviation...00z tafs...VFR conditions will prevail over the next 24 
hours. An unstable air mass will set the stage for widely scattered 
convective showers and isolated afternoon/evening thunderstorms 
(ts). An isolated thunderstorm began just after 330 PM in Jefferson 
County and has moved north into Wasco County. This ts may move to 
kdls from 00z-02z. Scattered showers over the southern Blue 
Mountains will move north to kykm, kpdt, kalw, and kpsc over the 
next hour or two. In central Oregon showers have been slow to start 
this afternoon, but still think potential exists for showers and 
thunderstorms in the vicinity at from 00z to 03z this evening. As such krdm and kbdn have 
thunderstorms in the vicinity in addition to -shra starting at 00z and ending at 03z. The 
showers and isolated ts will move north through about 04z and then 
dissipate when instability from daytime surface heating is depleted. 


Another round of showers will develop ahead of a cold front between 
09-11z in the western part of forecast area and then move eastward 
into the lower Columbia Basin and the Blue Mountains by around 
13z-14z/18th. Isolated nocturnal ts will occur late tonight in the 
line of showers along and ahead of the cold front. Then after 
daybreak Tuesday isolated to widely scattered ts are expected 
through the day on Tuesday. Due to low probability of a ts passing 
over a taf site have used thunderstorms in the vicinity to indicate the possibility of ts in 
the area near a taf site. Potential for strong or severe ts tomorrow 
after 16z. Cannot rule out hail stones to 1 inch and surface wind 
gusts to 40-50 kts with the better organized ts. 


Ceilings should be above 8000 feet agl, but brief MVFR conditions 
will be possible around heavier showers and near thunderstorms. 


Winds will be westerly at 10 to 15 kts for remainder of this 
afternoon and early this evening with gusts to 25 kts until 05z 
before diminishing below 12 kts. Polan 


&& 


Preliminary point temps/pops... 
PDT 58 73 51 65 / 20 20 50 60 
alw 61 75 54 66 / 20 20 50 60 
psc 62 79 55 71 / 40 20 40 50 
ykm 58 75 52 68 / 40 30 40 40 
hri 61 77 55 70 / 30 20 50 50 
eln 56 73 51 66 / 40 30 50 40 
rdm 51 68 47 62 / 30 30 50 50 
lgd 54 71 50 60 / 20 30 60 70 
gcd 49 72 48 60 / 20 30 60 60 
dls 59 74 54 67 / 40 30 50 50 


&& 


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


Threat index 
Tuesday : green 
Wednesday : green 
Thursday : 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. 


For additional weather information, check our web site at... 
www.Weather.Gov/Pendleton 


$$ 


91/76/76