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Science Forum Index » Environment Forum » Snowless in Portland
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| David Naugler |
 Posted: Wed Dec 17, 2003 10:05 am |
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From:
http://www.oregonlive.com/science/oregonian/index.ssf?/base/science/107157981493950.xml
Snowless in Portland
12/17/03
STUART TOMLINSON
Most of us can't remember, to paraphrase the poet Dylan Thomas,
whether it snowed 6 inches when we were 12, or 12 inches when we were
6, but chances are if you were 12 years old in Portland during the
winter of 1861-62, you had six good weeks of sledding.
"That was by far one of the most severe winters ever experienced in
the Pacific Northwest," said retired meteorologist George Miller. "It
really was six weeks of good sledding, and that is just unheard of
these days."
Indeed. Other than a surprise snowstorm on Nov. 19, when 1 inch was
officially recorded at the National Weather Service office on
Northeast 122nd Avenue, if it doesn't snow this winter in Portland it
will be the sixth winter in a row without a significant snowfall --
the longest such stretch in more than 60 years.
Experts disagree on the reasons. Some say global warming. Others say
it's part of a natural cycle, too vast and long to fit into neat
100-year or even 150-year patterns.
One says it can be attributed to the moving of Portland's weather
stations from place to place, and the growth of the urban heat island,
which won't allow temperatures to fall low enough for it to snow, or
that it's just a natural cycle of warm winter at the end of a little
ice age.
And what of the effects of sunspots?
Whatever the reasons, most of us can't recall the last time the
Columbia River froze over enough to allow cars to travel between
Portland and Vancouver, as happened in December 1924.
Or of snowdrifts 3 and 4 feet high in downtown Portland, as they were
in December 1884, when it snowed more than a foot, rained hard and
then snowed another 8 inches.
"A blinding snow storm is most unwelcome in less favored regions than
this, and here where no preparations are ever made for extreme
weather, such a storm as prevailed yesterday unsettled everybody. It
paralyzed business and worked discomfort to all classes of people. . .
.. The snow was too much for the streetcars. There was a very small
attendance at each of the public schools when the tardy bell rang in
the morning."
The Oregonian, Dec. 17, 1884
In the winter of 1861-62, it started snowing on Dec. 22 and covered
Portland and all of the Northwest with 1 to 3 feet of snow. Most of it
didn't melt until mid-March.
It was 10 years before official record-keeping began, but Miller has
found that from 1849 to 1870 more than half the winters were cold and
snowy in Portland, and the Willamette and Columbia rivers froze over
four times. Official record-keeping began in Portland on Nov. 1, 1871.
When determining temperature and rainfall averages, climatologists
often look at 30 years of weather data. A look at 30-year increments
of winter weather in Portland shows a marked decline in cold weather,
and hence, snowfall, in the last 132 years.
From 1871 through 1901, there were 19 winters in Portland when more
than 10 inches of snow fell; 12 with more than 20; seven with more
than 30; three with more than 40; and two that got 50 inches or more
of snow, including 60.9 inches during the winter of 1892-93.
"There were some bad winters back then -- far more winters with snow,
and substantial snow of as much as 25 inches with very cold
temperatures," said Miller, who spent 35 years with the National
Weather Service. "We had by far more snow back in the 1800s and the
first half of the 1900s than we're seeing today. . . . There has never
been a succession of mild winters like we've had over the past 30
years."
From 1901 through the winter of 1930-31, there were 12 winters when
more than 10 inches of snow fell, and 11 similar winters for the 30
years from 1931-1932 through the winter of 1960-61.
But from the winter of 1961-62 through the winter of 1991-92, there
were only six winters with more than 10 inches of snow.
In the last 10 winters, Portland has had just one winter with more
than 10 inches of snow, the winter of 1992-93. The last seven winters
have been equally snow-free. Only one, 1998-99 with 2 inches, had more
than an inch of snow.
"The only thing to look at is global warming . . . I don't know what
else to attribute it to," Miller said. "There has to have been a
change in the weather patterns, in the jet stream and the storm
tracks."
"The old-fashioned winter is largely the creation of more or less
imperfect memory and the fact that extraordinary weather makes a more
durable impression upon people's mind than ordinary weather. The
illusion is due in part to improvements in the heating of houses and
movements of the population from the natural environment of the
country to the artificial conditions of the town. It is well known,
too, that the city is warmer than the country. There is freer
radiation in the rural districts, and radiation is definitely retarded
under urban conditions by smoke screens, pavements and other
artificialities.
The Oregonian, March 23, 1919.
Is global warming -- the trapping of man-made gases that causes the
greenhouse effect -- really the cause for Portland's succession of
mild winters?
"This is what a lot of people are talking about right now," said
George Taylor, state climatologist. "The main theory holds that it's
all about global warming. . . . but the numbers just don't back that
up."
Taylor, who has studied Portland and all of Oregon's climate records
extensively, said Portland's weather statistics are flawed because the
weather station has been moved seven times since 1871, and the records
reflect the effects of Portland's urban growth in the last 100 years.
Those artificialities, as they were called in 1919, include
heat-trapping rooftops, buildings, roadways and parking lots -- better
known in scientific circles as the urban heat island.
Studies have shown that less soil and vegetation allow more solar
radiation to be absorbed and held by rooftops, buildings and pavement.
As a result, Taylor said, nighttime temperatures are warmer in the
city than in rural areas.
The temperature difference can be as much as 10 degrees in the summer,
and two to three degrees in the winter -- just enough to melt snow as
it falls through the atmosphere above the city.
In Corvallis, where a weather station has been located in a grass
field away from buildings, snowfall records are pretty consistent from
1889 through 1999. For 50 years, Portland's mean annual temperature
has gone from 52 to 55 degrees, a jump of three degrees, while
Corvallis' has only gone up half a degree.
"When we look at Corvallis and Portland, a very different pattern
emerges," Taylor said. "It shows a not very discernible long-term
trend. Without a doubt, temperatures in the past 25 years are warmer
than they were at the turn of the century. But are we really seeing a
long term change? I'm saying, maybe not. What we need are a couple of
things to say that -- a longer period of records, the longer the
better, and an unbiased weather station."
Instead of global warming, Taylor said, what we're seeing may be the
result of gradual warming from the last little ice age, a cooling of
global temperatures from about 1350 to about 1800. The warming started
in the mid-1850s, and 1860s, and continued into the mid-20th century
before leveling out.
That, he said, is a better reason for the global shrinking of glaciers
than global warming, and may be the cause of Portland's
less-than-snowy winters. "Glaciers are more affected by precipitation
than temperatures," Taylor said.
The link between sunspots -- which appear periodically on the sun's
surface and are associated with disturbances in the Earth's magnetic
field -- and climate is debatable, Taylor said, but it makes sense to
assume that there is an influence.
"We have been in a solar cycle peak, a pretty significant one that
peaked in 2001. Some climatologists have suggested that during the
next five or six years we will see distinct cooling worldwide."
Will that lead to more snowy winters in Portland? Will the children of
2020 walk between Portland and Vancouver across the Columbia River the
way they did in January 1868, when the river froze solid?
Don't put that snow shovel in the attic just yet.
When they met to discuss their winter forecasts in October, members of
the Oregon chapter of the American Meteorological Society agreed on
one thing: Portland is way overdue for a significant snowstorm.
Winter officially starts with the solstice at 11:04 p.m. Sunday.
Stuart Tomlinson: 503-294-5940; stuarttomlinson@news.oregonian.com |
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