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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 66 °
• Low: 45 °
• Partly Cloudy

• Thursday
• 
• High: 63 °
• Low: 43 °
• Partly Cloudy

• Friday
• 
• High: 61 °
• Low: 41 °
• Partly Cloudy

• Saturday
• 
• High: 70 °
• Low: 46 °
• Partly Cloudy

• Sunday
• 
• High: 66 °
• Low: 50 °
• Mostly Cloudy

Area forecast discussion 
National Weather Service Portland or 
308 am PDT Wednesday may 16 2012 


Synopsis...the cooldown continues today as our strong upper level 
ridge moves off to the east. Strong onshore flow will continue as a 
weak upper level trough deepens the marine layer tonight and 
Thursday. Low clouds are expected to return to the coast this 
morning...then spread well inland with patchy drizzle possible as the 
upper trough moves onshore tonight and Thursday morning. Most areas 
will remain dry through the weekend. A return to wet weather is 
looking increasingly likely for next week. 


&& 


Short term...satellite fog product shows low clouds are slow to 
return to the coast this morning...just a few patches beginning to 
develop around Astoria and also spreading northward from the Coos Bay 
area. Most models...suggest the low clouds will continue to develop 
over the next few hours...becoming widespread along the coast by 15z. 
While this may be a little hasty...the general idea looks good with 
increasing low clouds along the coast. Inland areas probably too dry 
for low clouds this morning with dewpoints falling into the 30s some 
areas. 


Without low clouds to start the morning...inland areas should see 
filtered sunshine with variable high clouds throughout the day. 
Onshore pressure gradients start off the day at 8 mb from kast-kdls 
and should only get stronger as the day progresses...so the seabreeze 
will remain brisk throughout the day. While this will keep 
temperatures cooler than Tuesday...the air mass aloft is cooling as 
well. European model (ecmwf)/GFS show 1000-500 mb thicknesses falling throughout the 
day...and 850 mb temperatures will be 2-4 degree c cooler than Tuesday. As a 
result temperatures should be capped in the lower to middle 70s inland today. 


One big forecast question is whether or not low clouds will solidify 
along the coast by tonight...then deepen and spread inland Thursday 
morning as a weak upper trough moves across the district. NAM bufr 
soundings suggest despite the cooling aloft...a decent marine 
inversion remains through Friday morning. This should keep coastal low 
clouds intact as they spread inland tonight/early Thursday...assuming they 
form at all over the next 12-24 hours. Going along with this 
Assumption...Thursday looks fairly cloudy for the district with some 
drizzle or isolated showers possible over the higher terrain. 
Extensive low clouds also look possible for Thursday night/Friday morning as 
onshore flow continues and the marine layer remains deep. The cloud 
cover and cooler air mass will likely send temperatures to below 
normal levels by Thursday or Friday. 


Tricky forecast though...as there remains the possibility coastal low 
clouds never solidify and spread inland. There is also the 
possibility the cool air aloft associated with the upper trough mixes 
out the marine layer completely by Thursday. Either situation would 
result in more sunshine for Thursday and Friday...and temperatures a little 
warmer than our current forecast. Weagle 


Long term...looks like another dry weekend as weak high pressure 
builds across Washington and Oregon. Temperatures will gradually warm 
back up as shortwave upper level ridging warms the air mass aloft. 
Highs may return to a few degrees above normal...middle to upper 70s 
inland...for Sunday. Eventually a strong Pacific jet will shove the 
upper ridge eastward...with a frontal system approaching the coast by 
Monday. While some outlying models have brought rain inland 
Sunday...the consensus still limits the rain threat to the north 
coast Sunday afternoon. We continue to lean toward the consensus 
solution keeping most areas dry Sunday. After that...models continue 
to show a more troughy pattern...bringing a return to cool and wet 
weather early next week. Weagle 


&& 


Aviation...VFR conditions dominating early this morning. However 
stratus slowly regenerating along the North Washington and south Oregon 
coast. Model relative humidity fields suggest MVFR ceilings around 1000-1500 feet 
with local IFR ceilings to develop in this morning on the coast...but 
not have much inland intrusion. There could be areas of scattered to broken 
ceilings around the keug area this morning where remaining higher 
moisture exists. VFR is expected to prevail this afternoon except 
for areas of MVFR continuing on the coast. 


&& 


Marine...marginal Small Craft Advisory winds over the waters 
though coastal observing locations with the exception of Newport 
jetty are below advisory criteria. Flow turns a little more to the 
west this afternoon so expect near shore winds to ease. However 
the coastal water zones west of 10 nm should remain in Small Craft 
Advisory criteria through at least Thursday morning...possibly into Thursday 
night. 


Advisory for steep hazardous seas verified at buoy 89 and just 
under elsewhere. So will continue with hazardous seas advisory 
in the north water. Overall trend is for the wave period to 
increase so hazardous conditions should decrease later in the 
morning. The prolonged northwest winds still appear likely to drive 
seas up to 10 feet by Thursday...before subsiding again Friday. 


&& 


Pqr watches/warnings/advisories... 
or...none. 
Washington...none. 
Pz...Small Craft Advisory for winds until 10 am PDT Thursday for 
waters from Cape Shoalwater Washington to Cascade Head or from 10 
to 60 nm-waters from Cascade Head to Florence or from 10 to 
60 nm. 


Small Craft Advisory for hazardous seas until noon PDT today 
for coastal waters from Cape Shoalwater Washington to Cascade Head 
or out 60 nm. 


Small Craft Advisory for winds until 8 PM PDT this evening 
for coastal waters from Cape Shoalwater Washington to Cascade 
Head or out 10 nm-coastal waters from Cascade Head to 
Florence or out 10 nm. 


&& 


$$ 


More weather information online at... 
http://weather.Gov/Portland 


This discussion is for northwest Oregon and southwest Washington from 
the Cascade crest to 60 nautical miles offshore. The area is commonly 
referred to as the forecast area.