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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 37-40 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.
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."
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.
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.
It is a gardening paradise. 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 |
Jan. |
Feb. |
Mar. |
Apr. |
May |
June |
July |
Aug. |
Sept. |
Oct. |
Nov. |
Dec. |
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Clear Days |
2.9 |
2.9 |
3.3 |
3.5 |
5.0 |
6.2 |
12.6 |
11.4 |
10.3 |
5.4 |
2.8 |
2.1 |
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Partly Cloudy |
3.6 |
3.8 |
4.9 |
5.8 |
7.2 |
7.7 |
8.5 |
9.6 |
8.1 |
7.6 |
4.3 |
3.3 |
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Cloudy Days |
24.4 |
21.5 |
22.8 |
20.7 |
18.9 |
16.1 |
9.9 |
10.1 |
11.6 |
18.0 |
22.9 |
25.5 |
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Rainy Days* |
18 |
15.6 |
16.9 |
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.
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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