Extreme
Weather of the
Pacific
Northwest
Cliff Mass
University of
Washington
The
extreme
side of
Northwest
weather
•The strongest non-tropical cyclones in the nation,
with the wind speeds of some equivalent to
category 1 or 2 hurricanes.
•The greatest annual rainfall in the continental
U.S.
•World-record snowfalls in our mountains
•Billion dollar floods
•The greatest avalanche losses in the continental
U.S.
•Localized hurricane-force winds
•and many more …
John Meares,
1788, off of Cape
Flattery of the
Olympics
Peninsula
The force of southerly storms was evident to every eye;
large and extensive woods being laid flat by their
power, the branches forming one long line to the
North West, intermingled with the roots of
innumerable trees, which have been torn from their
beds and helped to mark the furious course of their
tempests.
Extreme Northwest Precipitation
Greatest Annual Precipitation in the Continental U.S.
Largest Precipitation Differences
Annual
Precipitation
SW Olympic Slopes-Hoh Rain Forest: 150-170 inches yr-1
Sequim: Haven for Retirees
15 inches a year—
similar to LA!
Our region has extreme differences in annual
precipitation
Why such extremely
dry summers?
Few thunderstorms
Fewer thunderstorms!
The most costly
extreme weather of
the Northwest:
Flooding
Most are associated with the
“Pineapple Express”
A relatively narrow current of warm, moist air from the
subtropics…often starting near or just north of Hawaii.
a.k.a.
Atmospheric
rivers
A Recent Devastating Pineapple Express:
November 6-7, 2006
Dark Green: about 20 inches
Mount Rainier National Park
18 inches in 36 hr (Nov 8, 2006)
Extreme Winds
The region’s
most extreme
Inauguration
winds are
Day
Storm
associated
January 29,
1993
with large low
pressure areas
from off the
Pacific
1993 Inauguration Day Storm
Northwest Cyclones
• Our strong low-pressure storms are
midlatitude cyclones…areas of intense low
pressure that derive their energy from the
the north-south variation of temperature in
the midlatitudes.
• In contrast: tropical cyclones…like
hurricanes… get their energy from the
warm sea surface of the tropics.
1000 miles
1000 miles
Hurricane Ivan
Our storms are bigger than theirs!
Trees—our force multiplier
Compared to their wimpy
tropical palms
The Most Extreme Northwest Windstorm: The
Columbus Day Windstorm of 12 October 1962
Max Winds
(mph)
Columbus Day
Storm 1962
Probably the
most intense
non-tropical
cyclone to hit
the continental
U.S. in a
century
Columbus Day 1962: At Cape Blanco there were
150 mph with gusts to 179. Strongest winds on
bluffs and windward slopes of coastal orography
Extreme Local Winds
February 13
1979: The
Hood Canal
Storm
Winds over 110 mph destroyed the Hood Canal Bridge
Cost to replace: over 100 million dollars
The Hood Canal Storm
February
13
1979:
The
Hood
Canal
Storm
But there is another strong wind
situation for the San Juans: the
Fraser River Gap Winds
Fraser River Gap Windstorms
December 28, 1990
Fraser River NE Gap Flow
Gusts
above 90
mph
Max Winds, 28 Dec. 1990
December 28, 1990
Is Our Weather Getting More
Extreme?
There has been a lot discussion in
the media and the scientific
literature suggesting that western
U.S. extreme precipitation events
have already increased in
intensity or will soon increase
under anthropogenic global
warming
Press Advisory
National Wildlife Federation
November 17, 2009
Contacts:
XXXX (name removed)
Senior Environmental Policy Specialist
National Wildlife Federation, Pacific Region
YYYY (you know her!)
Climate Scientist
National Wildlife Federation
… Global warming is exacerbating extremely heavy rainfall
events, and recent climate change modeling suggests that these
pineapple express storms are no exception. “Heavier rainfall
events combined with significant snowmelt in midwinter is just what
the Pacific Northwest should expect from global warming,” said Dr.
YYYY, climate scientist, National Wildlife Federation.
…. Recent data[1] suggests that as a result of climate change, the
largest storms (i.e., those that are most likely to cause flooding)
will trend toward producing increasingly larger quantities of
precipitation.
Other Claims
• Recent big storms are just signs of natural variability.
• Global warming is an unproven theory we don’t have
to worry about, and recent more extreme weather
events don’t have anything to do with it.
The Truth is More Complex
Are there trends in
major precipitation
events?
• Trends in top 60
two-day
precipitation events
at stations along the
coast for 19502008.
• Not uniform.
When it Rains it Pours Used the Kunkel
Approach for 1-day rainfall (1948-2006)
• More over Wa, LESS over Oregon, little
trend, N. CA.
West Coast Windstorms Are
Following the Same Pattern
• Increasing number of major windstorms
from northern Oregon into southern BC
• Decreasing numbers to the south.
Why Simple
Arguments Could
Fail
• A number of theoretical, modeling, and
observational studies have suggested that the jet
stream may move northward under global
warming.
• Strong storms and heavy rainfall (pineapple
express situations) tend to follow the jet stream.
• It is possible that the “action” could move north of
us under GW, with less major storms.
Bottom Line
• Global warming will substantially change northwest
climate in the latter half of this century--particularly
bringing higher temperatures and lesser snowpack.
• Except for temperature, the atmospheric sciences
community is not yet sure whether global warming
will produce a change in extreme weather frequency
or intensity over the Northwest.
• This is an area of active research and we should know
a lot more in five years.
• Until then, be wary of simplistic, dire predictions.
The End
Mercer Island: Hanukah Eve Storm