The Weather of the Pacific
Northwest
Cliff Mass
University of Washington
Seattle Public Library
November 15, 2008
On June 24, 1947, Kenneth Arnold,
flying a small plane between Chehalis
and Yakima, spotted a group of
“saucer-like” objects over Mt. Rainier
Thus was born
the UFO craze
that continues
until this day
During a recent
presidential debate
on October 30,
2007, candidate
Dennis Kucinich
admitted that he
saw a UFO while
staying at Shirley
McClain’s home.
What did both of these sightings
have in common?
Both occurred over Washington State
near Mount Rainier
Could these strange apparitions been
caused by a frequent weather feature
around Mt. Rainier and other major
mountains of the area?
a mountain wave cloud
Picture courtesy of Art Rango
Picture Courtesy of Darlisa May Black
Mountain Wave Clouds
Wave Clouds
Northwest Weather 101
The weather of the Pacific Northwest is dominated
by local weather features, most forced by our
regional terrain.
During the winter the mountains block the
cold air from the interior.
Cold
Air
Cold Air from the Continental Interior
Has a Hard Time Reaching Western
Washington
Weather
Systems and
Storms
Generally
Move From
West
To East:
Thus, Our
Weather
Comes From
Off
The Mild
Pacific
The Book
• My attempt to write a
comprehensive introduction to
Northwest weather suitable for
the layman.
• Includes everything from the
big storms and local weather
features, to climate, weather
prediction and how to read the
skies.
• Full of color illustrations and
photos.
Thanks
• To UW Press for publishing it and the Stroum
Foundation for partially underwriting it.
• Beth Tully for her excellent work on the
figures.
• Editor Mary Ribesky and Book Designer Ashley
Saleeba…among many at UW Press.
• My wife Caroline and sons Aaron and Nathan
for their good natured tolerance of the
project.
Rainshadows
• People are always talking about the rain
around here.
• But what is perhaps even more interesting is
where it is NOT raining.
• The Northwest has an amazing collection of
rainshadows…
Sequim: Haven for Retirees
Why a rain shadow?
Annual Precipitation
• Sequim: 15.97 inches
• Los Angeles: 14.89 inches
Rainshadows can move: like this week!
9:40 AM looking west towards the
Olympics
Seattle Really Isn’t That Wet—partially
because we are often in the
rainshadow of the Olympics
The Northwest Has a Mediterranean Climate
The Big Storms of the Pacific
Northwest
Our major
windstorms
are
generally
associated
with strong
low
pressure
systems,
called
midlatitude
cyclones
Inauguration Day Storm January 20, 1993
Chanukah Eve Storm: 18-h forecast for 10 PM December 14, 2006
L
Mercer Island, December 15, 2006
The was
extraordinary—
made far worse
by the heavy
precipitation of
the previous
month.
The Most Extreme Northwest Windstorm: The
Columbus Day Windstorm of 12 October 1962
Max Winds
(mph)
Columbus Day
Storm 1962
Columbus Day 1962: At Cape Blanco there were
150 mph with gusts to 179! Strongest winds on
bluffs and windward slopes of coastal orography
The Great Coastal
Gale of December
3-4, 2007
A recent, highly
unusual storm:
long-lived
hurricane-forced
winds, intense
rainfall, and
flooding
Massive damage along the N. Oregon
and S. Washington coast
While record-breaking rain fell over
the mountains of SW Washington- 20
inches over a little more of day.
Massive flooding along the Chehalis River
Landslides: which led to the retirement
of the current lands commissioner
For nearly all NW windstorms the
strong winds generally last only a few
hours.
Most windstorms don’t cause flooding
Why was this event so unusual?
4 PM Sunday Dec. 3, 2007
L
The End
Global Warming: What will be the
effects on the Northwest?
Have we seen warming already?
Is the snowpack melting?
Climate Model Output for 2100
Snowpack hasn’t changed in the last
30 years
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
+0.2
+0.4
+0.6
Air Temperature Trend (1979-2005)
Change in Surface Air Temperature (°C) from 1979-2008
+0.8
+1.0
+1.2
+1.4
Pacific Decadal Oscillation (PDO)
PDO is thought to be a natural mode of atmospheric variability
Negative phase of PDO associated with greater snowpack in NW.
A Favored Area?
• The Northwest is downwind of the eastern Pacific and
thus our snowpack is controlled by the Pacific
temperatures.
• The eastern Pacific has not warmed up during the past 30
years.
• Global climate models suggest the eastern Pacific will
warm more slowly than most locations.
Averaging a collection of the best climate models over the Pacific
Suggests the Same Thing for the Future
(a) SST
SST
(b) Tsfc
0.0
+0.2
+0.4
(c) T850
+0.6
Air Temp
+0.8
+1.0
+2.0
+3.0 °C
850 mb
Stoelinga, Albright and Mass 2008
Predicted linear trend of November-March mean temperature for 2000 to 2025
(°C), as predicted by the ensemble of climate models used in the IPCC AR4 report.
Shown are the ensemble means of (a) sea-surface temperature, (b) surface air
temperature, and (c) 850-hPa temperature.
Summary
• Global warming is certain, the question is its magnitude and
regional effects.
• The magnitudes of the changes will vary geographically, and
the Northwest may see weakened and delayed effects,
because of our location downstream of the Pacific, and the
nature of our storms.
• Global warming is a serious, but complicated issue, and some
of the ideas being thrown around by the popular press and
well-intentioned but misinformed people are not necessarily
correct.
• We lack strong evidence at this time of any major global
warming threats to the region or the parks during the next
several decades
Annual
Precipitation
SW Olympic Slopes-Hoh Rain Forest: 150-170 inches yr-1
The Northwest Gets Fewer
Thunderstorms Than Almost
Anywhere in the U.S.
Why?
• The main reason is the cold water of the
Pacific Ocean.
– Colder surface temperatures
– Less water vapor over cold water.
Local Weather Features of the
Region
Puget Sound Convergence Zone
Wind Speed Simulation (red indicates about about 35 mph)
Troutdale
Winds over 110 mph destroyed the Hood Canal Bridge
Cost to replace: over 100 million dollars
February
13
1979:
The
Hood
Canal
Storm