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Portland Weather
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Weather − Specifically Rain
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 Portlanders
call the rains Portland mist. The mist brings us a lush green year
around and an ideal climate for gardeners. The amount of rainfall in the
Portland area is about 37 inches per year −
the same as most US east coast cities. Whereas it can rain 2-3 inches
in a hour or two in Washington, DC, or many mid-western areas, it will take
days to accumulate 2-3 inches in Portland.
A total of about 40 inches
of rainfall (includes rain, snow, hail, etc.) is Portland's mean annual
precipitation. We have four months of very rainy weather, four months
of 50-50 rainy days, and four months of very dry weather. Here are
the rain numbers:
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Fifty-five percent of the rain comes in four months:
November, December, January, and February.
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Another 32% comes in March, April, May, and October.
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In the other four months (June, July, August, and
September), Portland receives five inches of rainfall.
The above illustration is Patrick Burke's Portland with
Rain. Patrick
Burke Photography & Graphic Design features the following services:
business portraiture, people, pets, products, photo restoration, and fine
art photo illustration.
Coping with the Rain
 Don't
let anyone kid you. It can get disheartening. Coping with the
rain during the winter months is the challenge. Portlanders read,
go to the movies, and find dry places like Eastern Oregon. It's a
good time to travel. The good news is that it is never really cold
as evidenced by the Average Temperatures chart below.
Think positive. Rain is good for the complexion as
your mother may have told you as a kid when you couldn't go outside to play
because of the rain. Dolly Parton put a positive twist on it, "The
way I see it, if you want a rainbow, you gotta put up with the rain." The
comic strip, BC, added
their dry sense of humor with the strip above.
Carl Abbott, professor of Urban Studies at Portland State
University has this to say about Portland weather in his book called
Greater Portland: Urban Life and Landscape in the Pacific Northwest:
 The
most common understanding of Portland's climate is grayness. Because
the sunny weeks of August lack even the drama of lightning storms, it
is the low winter sky that attracts notice - the gray blanket of drizzle,
the short winter light. Clouds are great gray sponges wrung out against
the wet slope of the Cascades. The winter weather can nourish
deep depression. But the gray months can also be soothing, muffling,
twilight weather, thinking weather. Portlanders outpace most of
the nation in magazine subscriptions. They are avid bookworms
and science fiction fans who spend 37 percent more than average Americans
on reading matter.
Lauren Kessler, writer and
director of the Literary Nonfiction Program at the University of Oregon,
puts a romantic twist on the rain. Lauren admits it took her a few
years to appreciate a Western Oregon winter. She moved to Oregon in the
late 70s. Here are Laurel's words:
 I
love the rain. I don't mean I grudgingly appreciate its ecological necessity.
I don't mean I've learned to tolerate it. I don't mean I wait it out,
flipping through the calendar to see how many more pages until the sun
might break through. I mean I love it. I love everything about
it. I love falling asleep under a down comforter in the dead of winter
with the windows thrown open to the hiss of rain. I love waking up to
the soft aqueous light that is a painter's dream and listening to the
rush of water in the culvert. I love the thrum of rain against the house
on a dark afternoon with potato leek soup simmering on the stove.
Sallie Tisdale's article in
The Oregonian on December 16, 2007 is entitled, "Our
Blessed, Bountiful, Horrible Rains." Below is a paragraph from
her story:
 I
spend time regularly in a cabin near Mount Hood, and more than anything
this has changed the way I see the rains. Winter and rain are best shared
with trees and stones. I listen to the peculiarly comforting sound of
rain falling on the cones and needles and brushy bark, running in rivulets
down to the river below. Thomas Merton also spent rainy winter nights
alone in a cabin. There he wrote of the "enormous virginal myth" that
is rain -- "a whole world of meaning, of secrecy, of silence, of rumor."
We'll move on with after this
quote by Langston Hughes, "Let the rain kiss you. Let the rain beat upon
your head with silver liquid drops. Let the rain sing you a lullaby."
Snow in Portland
Yes, we get snow in Portland.
If you read the official record from the National Weather Service, you will
not get an accurate picture of what really happens about snow in Portland.
The official record doesn't tell the entire story because the National Weather
Service office is in Northeast Portland and at a low elevation. It is an
entirely different story at higher elevations. Snow forecasts always
bring with them an "elevation" factor such as, "1-3 inches of snow is forecast
for late afternoon at elevations of 500 feet and higher." Here is
a good example that occurred in late December 2003:
On Monday, some parts of
the West Hills got 7", Salem got 6" and Oregon City 5.5." Moving toward
the Coast Range, Buxton recorded 13", while in the shadows of Mount
Hood, Government Camp got 28" and Timberline 42". By late afternoon
Wednesday, 3.7 inches of snow had fallen at the National Weather Service
office in Northeast Portland. With the half-inch that fell Monday (December
29), 4.2 inches was the most snow recorded for a single month in Portland
since February 1993, when 6.6 inches fell. By late Wednesday morning,
the snow had turned to rain in downtown Portland but continued to pile
up at higher elevations and closer to the gorge.
So the official record will show 4.2 inches. But
if you live in the West Hills (elevations above 500 feet), you were shoveling
seven inches or more.
January 1950 was a very cold
month statewide, with frequent snowstorms. For the state as a whole, snow
was the heaviest during this January than ever before since the beginning
of weather record keeping, which began in 1890. Portland received
close to two feet of snow in ten days. Portland's all-time record
low was also set in 1950 when it reached three below zero on February 2.
Portland's snowfall for December
2008 totaled 18.9 inches and December 2008 also marked the second-snowiest
month in Portland's recorded history, bested only by the record set in the
Rose City in January, 1950 with 41.4 inches. During the period of 1871 to
the present, Portland's all-time records for snowfall include, at number
one, the winter of 1892-93, with 60.9 inches of snow. The winter of 1949-50
came in third with a total of 44.5 inches, while the winter of 2008-09 totaled
23.6 inches. Climate scientists predict significantly less snow for us in
coming years as the planet's warming climate tilts the Northwest's precipitation
more toward rain.
Snow Christmas Day
The chances of snow on Christmas Day in the Portland area is about 1 in
100, according to an Associated Press report based on National Climatic
Data Center records from 1988-2005.
Visit the National Weather
Bureau's Web page entitled
Some
of the Area's Snowstorms. It provides an overview of major storms
in Oregon during the 1990s. The record: 224 inches at Timberline
Lodge on Mt. Hood during January 1950.
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Winter's Pineapple Express and Then Summer
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Portland is a mosaic of
microclimates. Usually the weather stats are reported from the
airport (northeast part of the city) and rainfall and temperature can vary
from the airport to other parts of the city. On
the same winter day, you can get rain, hail, and sun. Even within
the same hour. The West Hills may experience a significant snowfall
that brings trace amounts of snow to other areas. In the summer, traveling
from the West Hills (lots of trees and wind currents in the hills) heading
into Beaverton (west suburb) or across the river into east Portland, you
will notice a increase in the temperature.
Winter Portlanders
watch the northern Pacific for their weather. The winter rain happens
when low pressure builds in the Gulf of Alaska and the jet stream drops
southward to sweep across the northern states. The counterclockwise
swirl around the deep atmospheric low pumps moist Pacific air across Oregon
from the west and southwest, driving ashore band after ban of clouds.
Pineapple Express is the shorthand for especially juicy storms
of warmer air that pick up moisture from as far to the southwest as Hawaii
and drench the valleys and mountains. When a high pressure area builds
off the coast and the jet stream moves north, we are guarantee dry weather.
Summers are Grand
Summers are dry and weeks go by without rain. Mild temperatures and
low humidity. It is one of the best place in the USA during much of
June, all of July and August, and a good share of September. June
average seven days of temperatures to reach or exceed 80 degrees, July
usually sees 15 days, and August averages 15. Portland also sees an
average of 13 days of 90 degrees or above. The first frost is in early November, and the
last frost in early April.
280 Growing Days
Portland has close to 280 growing days according to Western Gardens
by Sunset Publications. Visit
Timber Press' gardening links to learn more about Pacific Northwest
gardening.
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Average Days per Month: Clear, Cloudy, and Rainy Skies
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Type of Day
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Jan. |
Feb. |
Mar. |
Apr. |
May |
June |
July |
Aug. |
Sept. |
Oct. |
Nov. |
Dec. |
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Clear Days
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2.9
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2.9
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3.3
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3.5 |
5.0 |
6.2 |
12.6 |
11.4 |
10.3 |
5.4 |
2.8 |
2.1 |
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Partly Cloudy
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3.6
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3.8
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4.9
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5.8 |
7.2 |
7.7 |
8.5 |
9.6 |
8.1 |
7.6 |
4.3 |
3.3 |
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Cloudy Days
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24.4
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21.5
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22.8
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20.7 |
18.9 |
16.1 |
9.9 |
10.1 |
11.6 |
18.0 |
22.9 |
25.5 |
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Rainy Days*
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18
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15.6
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16.9
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14.4 |
11.8 |
9.2 |
3.9 |
4.9 |
7.5 |
12.3 |
18.0 |
18.7 |
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Source: Western
Regional Climate Center in Reno, Nevada. The data is based on
daylight hours only. A clear day denotes zero to 3/10 average sky cover.
Partly cloudy is 4/10 to 7/10 tenths. Cloudy is 8/10 to 10/10 tenths.
*.01 inches or more of precipitation.
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Portland Weather Historical Data
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NOAA (National
Oceanic and Atmospheric Administration) keeps weather data for over 50 years
on Portland. Here are some of the numbers:
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Annual Sunshine - The suns shines about 48%
of the time. Out of a possible 267,955 minutes, Portland averaged
128,618 minutes of sunshine between 1951 and 1995.
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Winds - The prevailing winds in the summer
(April - September) is NNW at 6.5 -7.6 mph. The winter months
bring winds from the ESE.
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Relative Humidity - Average is 73% at 10 AM
and 59% at 4 PM. This data from 1961-1990.
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Rain - Nearly 90 percent of the annual rainfall
occurs from October through May.
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Hottest Day of the Year - The average high
on August 9 is 84 degrees, from 60 years of data (1949-2009) recorded
at the Portland Airport Weather Station. That means there's roughly
a 50-50 chance it will get hotter than 84 on August 9.
Record Rainfall On December 12-13, 1882, Portland
received 7.66 inches of rain in one 24-hour period and saw 10.75 inches
in two days. Portland's single-month rainfall record occurred in November
2006 when 11.92 inches fell. These facts were obtained from The
Oregon Weather Book by George Taylor and Raymond R. Hatton,
Oregon
State University Press, ISBN 0-87071-467-8 except for the single-month
record which happened after the book was published.
The National Weather Bureau's Web site has a section entitled
Oregon's Top 10 Weather Events of 1900s which tracks floods, snowstorms,
tornadoes, and wind storms.
In 1998, the Department of Geology at Portland State University
published a
report
(MS Word document) documenting the extent of landslides following the 1996
flood and evaluating the causes. The greatest concentration of landslides
in Portland was in the West Hills in the wind-blown loess of the Portland
Hills Silt Formation. A total of 705 slides were studied in the project.
 The
Weather Café™ by Rufus provides uniquely informative long-range forecasts
for specific patrons in the Pacific Northwest. Rufus' forecasts have
information of value, but even more, they show a sense of humor and are
fun to read. It is a free service for patrons from British Columbia
to northern California.
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Portland Average Rainfall and Temperatures
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Below you will find information about Portland rainfall
and temperatures from World Climate.
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Average Rainfall - Located at about 45.51°N 122.68°W.
Height about 48m / 157 feet above sea level.
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Average Temperature - Located at about 45.60°N 122.60°W.
Height about 12m / 39 feet above sea level.
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Average Maximum Temperature - Portland International Airport. Located
at about 45.60°N 122.60°W. Height about 8m / 26 feet
above sea level.
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Average Minimum Temperature - Portland International Airport.
Located at about 45.60°N 122.60°W. Height about 8m
/ 26 feet above sea level.
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Heating Degree Days - The cumulative number of degrees in a month
or year by which the mean temperature falls below 18.3°C/65°F.
Data from Portland International Airport.
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Cooling Degree Days - The cumulative number of degrees in a month
or year by which the mean temperature is above 18.3°C/65°F. Data
from Portland International Airport.
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Factors Responsible for Portland's Climate
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The mountains (Coastal to the
west and Cascades to the east) along with Portland's latitude and
proximity to the Pacific Ocean, determine the climate. Here are some
of the factors mixed with general information that create the weather in
Portland.
Air Flow
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Air that crosses the Coast Range cools as it moves
east, dropping large amount of precipitation on the coastal mountains.
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The air that flows over Portland is drier than the
air that originally moved in from the ocean.
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Winds are predominately southerly during with mild
rainy spells in the winter.
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In the winter, the cold easterly winds also bring
the coldest air to the Portland area.
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During the summers, northwesterly winds bring cool
air from the Pacific Ocean down along the Columbia River.
Rain
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The lush conifer forests that flourish in Western
Oregon receive most of the
moisture from the storms that roll in off the Pacific Ocean. Portland
receives the remaining moisture and eastern Oregon very little.
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Many areas in the Coast Range receive between 180-200
inches of rain per year. Average rainfalls for coastal cities
is 60-80 inches per year.
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In parts of southeast Oregon (high desert), average
rainfall can be as low as 6-8 inches per year.
Temperatures
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Temperatures below zero degrees are rare, occurring
only six times over the last 125 years!
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Most temperatures during the winter reach the 40s
during the day and fall back into the low to middle 30s at night.
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Summer can be quite warm, with the temperatures frequently
reaching the middle 90s, although these warm days do not last long before
the cool marine air arrives with temperatures in the 70s.
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Temperatures above 100 degrees are rare.
Mountains
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The Coast Range provides the Portland area limited
shielding from the Pacific Ocean storms.
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The Cascades offer a steep slope for orographic lift
of moisture-laden westerly winds, resulting in moderate rainfall for
the region.
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The Cascades also act as a barrier, preventing the
colder continental air masses originating in the arctic areas of Canada
from invading western Oregon. Occasionally, however, cold air does work
its way into western Oregon through the Columbia River Gorge.
Storms
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Destructive storms are infrequent in the Portland
area. Surface winds seldom exceed gale force (wind speeds sustained
at 50 mph or greater) and have rarely exceeded 75 mph. Thunderstorms
can occur during any month, but are not common.
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Occasionally, thunderstorms produce funnel clouds,
but tornadoes are exceedingly rare.
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Portland Seasons
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 The
winter season is characterized by mild temperatures, cloudy skies
and rain. Winds are predominately either southerly with mild rainy
spells, or easterly during colder dry spells. Outbreaks of cold arctic air
from east of the Cascades will occasionally spill into the Portland area,
bringing cold blustery east winds. If the east winds occur when the
rain is falling over the metropolitan area, a shallow layer of cold air
forms along the Columbia River. In and near this cold sub-freezing
air, freezing rain and even snow will occur over eastern and northern Portland.
Spring is a transitional
time as the weather patterns shift from winter to summer. As a result, March
and April are wet and cool, while May and June turn drier. Temperatures
during May and June often take a roller coaster ride, ranging predominantly
in the 60s and 70s, occasionally reaching the 90s for a day or two.
Even though the number of rain days decrease in May and June, there are
still many cloudy days.
Summer finally arrives
in middle to late June, when the temperature is finally able the reach the
80s on a daily basis. Northwesterly winds bring cool air from the Pacific
Ocean down along the Columbia River. Summer can be quite warm, with
the temperatures frequently reaching the middle 90s, although these warm
days do not last long before the cool marine air arrives with temperatures
in the 70s. Temperatures above 100 degrees are rare.
Autumn is the reverse
of spring, with many warm days in September. By the middle of October, the
rains are beginning to arrive. In addition, cooler temperatures arrive,
with afternoon highs in the 50s and 60s. Fog begins to occur on a
nightly basis during late October and November, with visibilities often
under one mile. However, fog varies by location, with the difference
frequently depending on the altitude.
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