Extreme Weather of the Pacific Northwest
Cliff MassUniversity of Washington
•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 …
The extreme side of Northwest weather
The force of southerly storms was evident to The force of southerly storms was evident to every eye; large and extensive woods being laid every eye; large and extensive woods being laid
flat by their power, the branches forming one flat by their power, the branches forming one long line to the North West, intermingled with long line to the North West, intermingled with
the roots of innumerable trees, which have the roots of innumerable trees, which have been torn from their beds and helped to mark been torn from their beds and helped to mark
the furious course of their tempests.the furious course of their tempests.
John Meares,1788, off of Cape Flattery of the Olympics Peninsula
Extreme Northwest Precipitation
Greatest Annual Precipitation in the Continental U.S.
Annual Precipitation
Largest Precipitation Differences
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 annualprecipitation
Why such extremely dry summers?Few thunderstormsFewer 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 Park18 inches in 36 hr (Nov 8, 2006)
Extreme Winds
InaugurationDayStormJanuary 29,1993
The region’s most extreme winds are associated 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.
Hurricane Ivan
1000 miles 1000 miles
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
Winds over 110 mph destroyed the Hood Canal Bridge Cost to replace: over 100 million dollars
February 131979: The Hood CanalStorm
The Hood Canal Storm
February 131979: The Hood CanalStorm
But there is another strong wind situation for the San Juans: the
Fraser River Gap Winds
Fraser River Gap Windstorms
December 28, 1990
Max Winds, 28 Dec. 1990Fraser River NE Gap Flow
Gusts above 90 mph
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 AdvisoryNational Wildlife FederationNovember 17, 2009 Contacts:XXXX (name removed) YYYY (you know her!)Senior Environmental Policy Specialist Climate ScientistNational Wildlife Federation, Pacific Region 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 1950-2008.
• 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