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Old 03-30-2011, 09:12 AM
 
99 posts, read 277,705 times
Reputation: 76

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Weather is an important concern for many prospective residents, so it's only natural that it comes up in these forums repeatedly. The purpose of this thread is to answer those inquiries with facts and informational resources (rather than opinion).

If you are going to post, please provide statistical summaries (weekly data, monthly data, yearly data), weather videos, timelapse videos, photos, and other links that serve to educate newcomers and give a fact-based glimpse into the full spectrum of Portland weather (this includes both mild weather and severe weather). No single post is expected to represent "the average year" or "the average month," but rather, a snapshot in time.

This is meant to be a neutral thread that is based in documented fact. Please refrain from posting subjective opinions. There are numerous old threads that provide subjective descriptions of what people have personally experienced in terms of the weather. Please refer to those threads for that type of discussion.

Take some time to peruse the National Weather Service (NWS) links – the documented averages provided in those links are useful for comparison purposes. They will help to provide a more balanced view in regard to what the weather norms are over a long period of time. In contrast, many of the posts in this thread will include short-term data that varies widely from the norm. This is to be expected because the weather fluctuates outside of the norm much of the time, and we are simply documenting the weather as it occurs.

Dr. Greg Forbes, a severe weather expert at The Weather Channel, offers a discussion about averages and about how the only "normal" for the weather is that it varies from day to day (see his blog and other links below). That said, please keep in mind that some of the severe weather days shown in this thread may be anomalies in the sense that they show record-breaking weather. Consult the NWS data before drawing any conclusions from a single post.

Average vs. "Normal" Weather: Weatherman Glenn Schwartz Breaks it Down (Video)
Average vs. "Normal" Weather: Dr. Greg Forbes' Weather Channel Blog
Misconceptions About What Is "Normal" for the Atmosphere: Chuck Doswell, Research Scientist


FOR OPINION-BASED POSTS PLEASE REFER TO THE THREADS BELOW (or start a new thread):

SEARCH TOOL
Search the Portland Forum for More Weather Threads
Search the Weather Forum for More Weather Threads


SPECIFIC QUESTIONS
Humidity
Cold Snaps
Severe Weather


MONTH BY MONTH DESCRIPTION
Month-by-Month Weather Description
What Does a Year Look Like?
October Weather
November Weather


PORTLAND RAIN
How Often Does it Rain in Portland?
Does it Really Rain All the Time in Portland?
Does it Really Rain Ten Months Out of the Year?
No, It Doesn't Rain for Nine Months Straight
Left Portland Because of the Rain
Love the City, Hate the Rain
Five Days of Rain in Portland
Do Your Kids Play in the Rain?
Can You Hear the Rain Hitting Your Roof?
I Love the Rain – It's a Pacific Northwest Thing


DOWNSIDES OF PORTLAND WEATHER
"Gloomy Season" Pictures
Seasonal Affective Disorder (SAD) – Moving to Salem
Seasonal Affective Disorder (SAD) – Moving to Oregon from Arizona
Brutal Assessment of How Most People Are Affected by the Rainy Season
The Clouds Are So Constant, Dark, and Heavy – I Find Them Depressing
One Resident's Description of "Portland Gloom"
Just How Gloomy is Gloomy?


BENEFITS OF PORTLAND WEATHER
"Gloomy Season" Pictures
Portland Has the Best Weather
Ten-Day Forecast with Sunshine
If the "Gloom" is so bad, then why do so many people live there?
Is There Anyone Out There Who Enjoys Rain and Clouds?


HELPFUL HINTS FOR PORTLAND WEATHER
Staying Active in Portland Weather
Tips on Adjusting to Portland Weather
How to Keep Your Spirits Up in Portland Weather
When to Visit to Experience the "Worst" Weather


GENERAL WEATHER FORUM
Current Threads
Overcast Weather
I Hate Sunny Days
Poll: Which is Worse, Zero and Sunny or 45 and Rain?
Poll: Do You Prefer Sunny & Mild or Overcast & Mild?
Poll: Do You Prefer Rain or Snow?
Poll: Which City Has Better Weather – Seattle or Chicago?


CITY VS. CITY
Portland vs. Ireland
Portland vs. Seattle (Is the Weather the Same?)
Portland vs. Seattle (More Rain and Fog in Portland?)
Portland vs. Seattle (More Rain in Seattle?)
Portland vs. New York
Portland vs. New York (short)
Portland vs. Michigan
Portland vs. Wisconsin
Portland vs. Wisconsin (short)
Portland vs. Chicago
Portland vs. Chicago vs. Phoenix
Portland vs. Colorado vs. California
Portland vs. Tucson
Portland vs. Texas

Last edited by sunscribble; 03-30-2011 at 10:27 AM..
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Old 03-30-2011, 09:13 AM
 
99 posts, read 277,705 times
Reputation: 76
Default Portland Rain

Portland does not make the Top 100 list in terms of average annual precipitation (City-Data). The average annual precipitation for downtown Portland was 42 inches per year for years 1871-2008 (National Weather Service – Annual Precipitation). That was 10 inches below #101 on the city-data list (Waterbury, CT at 52 inches).

However, Portland does have streaks that consist of many consecutive days with measurable rain (mostly light rain). An extreme example of such a streak would be Febrary 28 to May 8 of 2003, when 66 of 70 days showed measurable rain (Johnson). According to Weather Underground, half of those days had <0.10 inches of rain, and the other half had 0.10 to 0.94 inches of measurable rain each day. A total of 10 inches of rain fell during these two months (March and April 2003). The top ten wettest days that occurred during this time are listed below (Weather Underground – March 7, 2003):

March 07 - 0.94 inches
March 08 - 0.40 inches
March 09 - 0.43 inches
March 12 - 0.45 inches
March 21 - 0.45 inches
March 22 - 0.45 inches
--------------------------
March Total = 5.75 inches (vs. the normal 4.51 inches for March)*


April 12 - 0.42 inches
April 13 - 0.57 inches
April 17 - 0.36 inches
April 23 - 0.60 inches
--------------------------
April Total = 4.24 inches (vs. the normal 2.91 inches for April)*


*Portland Normals for March and April:
National Weather Service - Precipitation Normals
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Old 03-30-2011, 09:14 AM
 
99 posts, read 277,705 times
Reputation: 76
The National Weather Service is a great resource for Portland precipitation data:

PORTLAND RAIN

Graphs of Annual & Monthly Rainfall

Top 5 Wettest Months/Years

Top 10 Wettest Days

Record Rainfall in an Hour

Consecutive Days of Rain


DAILY NORMALS AND RECORDS BY MONTH

-----Jan & Feb

-----Mar & Apr

-----May & Jun

-----Jul & Aug

-----Sep & Oct

-----Nov & Dec
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Old 03-30-2011, 09:15 AM
 
99 posts, read 277,705 times
Reputation: 76
Default Overcast Skies

Portland is ranked #6 for cloudy weather in the contiguous United States (Weather Today). January, March, November, and December are the cloudiest months. The average number of cloudy days, partly cloudy days, and clear days for January has been 24, 4, and 2, respectively:

Cloudy, Partly Cloudy, & Clear Days

227 cloudy days per year--------(where clouds cover 80% to 100% of the sky)

71 partly cloudy days per year---(where clouds cover 40% to 70% of the sky)

67 clear days per year-----------(where clouds cover 0% to 30% of the sky)


The National Weather Service also provides information on the percentage of overcast hours in each month. For example, in January, 90-100% of the sky was covered with clouds 68% of the time, and 60-100% of the sky was covered with clouds 81% of the time:

Sky Cover Frequency (January through June)

Sky Cover Frequency (July through December)
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Old 03-30-2011, 09:16 AM
 
99 posts, read 277,705 times
Reputation: 76
Default A Cloudy Day in November...

AVERAGE NUMBER OF CLOUDY DAYS IN NOVEMBER
(Source: National Weather Service – Cloudy Days)

Cloudy Days (clouds cover 80-100% of sky)
24 cloudy days in January
22 cloudy days in February
23 cloudy days in March
21 cloudy days in April
19 cloudy days in May
16 cloudy days in June
11 cloudy days in July
10 cloudy days in August
11 cloudy days in September
17 cloudy days in October
24 cloudy days in November
23 cloudy days in December
-------------------------------
227 total cloudy days per year


Partly Cloudy Days (clouds cover 40-70% of sky)
4 partly cloudy days in January
4 partly cloudy days in February
5 partly cloudy days in March
6 partly cloudy days in April
7 partly cloudy days in May
8 partly cloudy days in June
8 partly cloudy days in July
9 partly cloudy days in August
8 partly cloudy days in September
8 partly cloudy days in October
4 partly cloudy days in November
5 partly cloudy days in December
------------------------------------
71 total partly cloudy days per year


Clear Days (clouds cover 0-30% of sky)
3 clear days in January
2 clear days in February
3 clear days in March
3 clear days in April
5 clear days in May
6 clear days in June
12 clear days in July
12 clear days in August
11 clear days in September
6 clear days in October
2 clear days in November
3 clear days in December
--------------------------------
67 total clear days per year


Here is a quick video that shows one of the 24 cloudy days that might occur in November:



Video #1 – A Cloudy Day in November
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Old 03-30-2011, 09:17 AM
 
99 posts, read 277,705 times
Reputation: 76
Default A Clear Day in November...

AVERAGE NUMBER OF CLEAR DAYS IN NOVEMBER
(Source: National Weather Service – Clear Days)

Cloudy Days (clouds cover 80-100% of sky)
24 cloudy days in January
22 cloudy days in February
23 cloudy days in March
21 cloudy days in April
19 cloudy days in May
16 cloudy days in June
11 cloudy days in July
10 cloudy days in August
11 cloudy days in September
17 cloudy days in October
24 cloudy days in November
23 cloudy days in December
-------------------------------
227 total cloudy days per year


Partly Cloudy Days (clouds cover 40-70% of sky)
4 partly cloudy days in January
4 partly cloudy days in February
5 partly cloudy days in March
6 partly cloudy days in April
7 partly cloudy days in May
8 partly cloudy days in June
8 partly cloudy days in July
9 partly cloudy days in August
8 partly cloudy days in September
8 partly cloudy days in October
4 partly cloudy days in November
5 partly cloudy days in December
------------------------------------
71 total partly cloudy days per year


Clear Days (clouds cover 0-30% of sky)
3 clear days in January
2 clear days in February
3 clear days in March
3 clear days in April
5 clear days in May
6 clear days in June
12 clear days in July
12 clear days in August
11 clear days in September
6 clear days in October
2 clear days in November
3 clear days in December
--------------------------------
67 total clear days per year


Here is a quick video that shows one of the 2 clear days that might occur in November:



Video #2 – A Clear Day in November
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Old 03-30-2011, 09:18 AM
 
99 posts, read 277,705 times
Reputation: 76
Default A Partly Cloudy Day in October...

AVERAGE NUMBER OF PARTLY CLOUDY DAYS IN OCTOBER
(Source: National Weather Service – Partly Cloudy Days)

Cloudy Days (clouds cover 80-100% of sky)
24 cloudy days in January
22 cloudy days in February
23 cloudy days in March
21 cloudy days in April
19 cloudy days in May
16 cloudy days in June
11 cloudy days in July
10 cloudy days in August
11 cloudy days in September
17 cloudy days in October
24 cloudy days in November
23 cloudy days in December
-------------------------------
227 total cloudy days per year


Partly Cloudy Days (clouds cover 40-70% of sky)
4 partly cloudy days in January
4 partly cloudy days in February
5 partly cloudy days in March
6 partly cloudy days in April
7 partly cloudy days in May
8 partly cloudy days in June
8 partly cloudy days in July
9 partly cloudy days in August
8 partly cloudy days in September
8 partly cloudy days in October
4 partly cloudy days in November
5 partly cloudy days in December
------------------------------------
71 total partly cloudy days per year


Clear Days (clouds cover 0-30% of sky)
3 clear days in January
2 clear days in February
3 clear days in March
3 clear days in April
5 clear days in May
6 clear days in June
12 clear days in July
12 clear days in August
11 clear days in September
6 clear days in October
2 clear days in November
3 clear days in December
--------------------------------
67 total clear days per year


Someone asked me how the day is rated if it's cloudy in the morning and then partly cloudy in the evening (a good question). My guess is that they take an hourly scan of the sky. This would give a cloud percentage for each hour of the day. Then you could add all of the readings together to calculate the average cloud percentage for the day. For example, if your morning percentage was 100% clouds, and your noon percentage was 70% clouds, with an evening percentage of 40% clouds, the average percentage would come out to be 70%. In this case, the day would be labeled as "partly cloudy" (with clouds covering 40-70% of the sky). (Of course, in reality they would do more than just three readings per day).


Here is a timelapse video that shows one of the 8 partly cloudy days that might occur in October:



Video #3 – A Partly Cloudy Day in October
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Old 03-30-2011, 09:19 AM
 
99 posts, read 277,705 times
Reputation: 76
Default Foggy Commute

I hope the last three videos helped folks understand what the cloudy day statistics really mean.

Now moving on to fog...

The number of days with dense fog in Portland is shown below:

DAYS WITH DENSE FOG
4.3 days in January
3.7 days in February
2.4 days in March
1.1 days in April
0.2 days in May
0.1 days in June
0.1 days in July
0.2 days in August
2.7 days in September
7.2 days in October
6.1 days in November
4.9 days in December
--------------------------------
32.9 days with dense fog per year


Here is a timelapse video that shows a foggy motorcycle commute in Corvallis:



Video #4 – Foggy Motorcycle Commute
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Old 03-30-2011, 09:20 AM
 
99 posts, read 277,705 times
Reputation: 76
Default Grey Blanket Overcast

Portland has many different types of clouds. For example, the bulbous, rainstorm type of clouds that were shown in Video #3 are quite often seen on partly cloudy days. In contrast, the widespread, grey blanket type of clouds that are typical of heavily overcast days in Portland are shown in Video #5 below. This type of overcast is more monotonous than the rainstorm clouds of the Rocky Mountains or the Great Plains. It is characterized by a flat shape, relatively monotone color, and persistent, blanket-like formation. If you look at the video, you can see how effective this type of overcast can be in regard to filtering out sunlight. It's not uncommon to see the entire Portland sky covered with a blanket of clouds like this, but you are more likely to see this type of overcast in winter, late fall, and early spring than in summer.



Video #5 – Grey Blanket Overcast
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Old 03-30-2011, 09:25 AM
 
99 posts, read 277,705 times
Reputation: 76
Default Steel Bridge Timelapse Videos

I stumbled upon a YouTube channel that offers 19 months of 24-hour timelapse videos of the Steel Bridge. These videos are all shot from the same location, looking east from downtown Portland towards the Steel Bridge. They mostly show the bridge and a nearby parking lot, but they also show the edge of the sky at the horizon, so it's possible to see a portion of the sky.

The only time the videos really vary is when the weather changes (for example, you can tell when the sun is shining, when the sky is overcast, and when it is raining). The videos are also helpful for showing the dimness of overcast days as compared with the brightness of sunny days. Please note that the videos are time-lapsed, meaning that clouds, rain, and sun all appear to pass through much more quickly than they do in real life.

I would recommend going to Weather Underground – History for Portland to view the highs, lows, precipitation, and cloud log for the day that you are viewing. Simply select the month, day, and year that you wish to view, and then click the "View" button (located below the blue bar). Scroll to the bottom of the page for hourly observations. You can also click on the "Monthly" tab and scroll down to see a monthly calendar that shows the highs, lows, and precipitation for each day of the month.

Overall, the year of 2010 saw 4.23 inches more of rain than the average (Total = 46.33 inches , Average = 42.10 inches). Compared with the average, February saw quite a bit less rain, but May, June, September, and December made up for that with significantly more rain than the average. The precipitation details for 2010 are shown below:

Normal vs. Actual inches 2010
-------------------------------
5.07 vs. 4.94 inches for January
4.18 vs. 2.80 inches for February
3.71 vs. 3.58 inches for March
2.64 vs. 2.92 inches for April
-------------------------------
2.38 vs. 4.75 inches for May
1.59 vs. 4.28 inches for June
0.72 vs. 0.60 inches for July
0.93 vs. 0.25 inches for August
-------------------------------
1.65 vs. 3.36 inches for September
2.88 vs. 3.87 inches for October
5.61 vs. 6.63 inches for November
5.71 vs. 8.35 inches for December
----------------------------------
42.10 vs. 46.33 inches for 2010


24-HOUR TIMELAPSE – 2010
List of Daily Videos for January
List of Daily Videos for February
List of Daily Videos for March
List of Daily Videos for April
List of Daily Videos for May
List of Daily Videos for June
List of Daily Videos for July
List of Daily Videos for August
List of Daily Videos for September
List of Daily Videos for October


FULL MONTH TIMELAPSE – 2010
Full Month of April
Full Month of May
Full Month of June
Full Month of July
Full Month of August
Full Month of September
Full Month of October
Full Month of November


24-HOUR TIMELAPSE – NOVEMBER
November 1, 2010
November 2, 2010
November 3, 2010
November 4, 2010
November 5, 2010
November 6, 2010
November 7, 2010
November 8, 2010
November 9, 2010
November 10, 2010
November 11, 2010
November 12, 2010
November 13, 2010
November 14, 2010
November 15, 2010
November 16, 2010
November 17, 2010
November 18, 2010
November 19, 2010
November 20, 2010
November 21, 2010
November 22, 2010
November 23, 2010
November 24, 2010
November 29, 2010
November 30, 2010


24-HOUR TIMELAPSE – 2009
List of Daily Videos for April
List of Daily Videos for May
List of Daily Videos for June
List of Daily Videos for July
The YouTube Video for August 28
The YouTube Video for August 30
The YouTube Video for August 31
List of Daily Videos for September
List of Daily Videos for October
List of Daily Videos for November
List of Daily Videos for December
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