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