northwest climate: the mean factors that influence local/regional climate: 1. latitude day length,...

Northwest Climate: the mean

Factors that influence local/regional climate:

1. Latitude

• day length, intensity of sunlight

2. Altitude

3. Mountain Barriers

4. Proximity to the ocean

• ocean currents

5. location relative to prevailing winds

Winter windsand pressure over the North Pacific

Summer windsand pressure over the North Pacific

“Aleutian Low” “Subtropical High”

HH

LL

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Oregon Climate Servicehttp://www.ocs.orst.edu

Northwest terrain maps the big-picture windsand storms onto a complex landscape

• localized cold air outbreaks

• the Puget Sound Convergence Zone

• rain shadows

“Arctic Blasts”

The Puget Sound Convergence Zone

http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?atx_n0r+/12h/30m










Annual average rain+snowfall: 1961-1990

The predictable part: seasonal rhythms

Puget Sound Precip

Upwelling winds at 48N

Amphitrite Pt SST

Oct Feb Jun

Oct Feb Jun

Oct Feb Jun Jan May Sep

InsolationInsolation

Year to year variations on the seasonal rhythms

Monthly Puget Sound Precip

Daily Upwelling winds

Monthly Amphitrite Pt SST

Northwest Climate Variability

Pollen records on the Olympic Peninsula

Crocker Lake

McLachlan, J. S. and L. B. Brubaker. 1995 Local and regional vegetation change on the northeastern Olympic Peninsula during the Holocene. Canadian J. of Botany.

alder

cedars

pines

df

1750 1775 1800 1825 1850 1875 1900 1925 1950 1975 2000Year

5.0

5.1

5.2

5.3

5.4

5.5

Log10 mean flow, The Dalles, OR (cfs)

Source: Gedalof, Z., D.L. Peterson and Nathan J. Mantua. (2004). Columbia River Flow and Drought Since 1750. Journal of the American

Water Resources Association.

The Dust Bowl (1929-1931) was probably not the worst drought sequence in the past 250 years

(based on Columbia Basin Tree-ring chronologies)(based on Columbia Basin Tree-ring chronologies)

red = observed, blue = reconstructed

PNW climate variability

1. What does our region’s climate history tell us about “natural variability”?

2. How is climate variability experienced in the Pacific Northwest? * are there patterns within the region? * are there preferred frequencies of change (year to year, decade to decade, etc.)

3. Why does our climate vary?

Warm and cool (or “wet” and “dry”) halves of the year: oct-mar versus apr-sep

What do you see?

Characteristics of variability?

• Lots of year-to-year variability in both halves of the year; longer-term variations– Multi-decadal “cycles” and century long trends

• temperatures and precipitation are more variable in cool season than in warm season

Washington State Oct-Sept Average Temperature

35

38

19801960194019201900 2000

40

Washington State Oct-Sept Total Precip

4

6

19801960194019201900 2000

Riffe Lake, west slopes of the Cascades

Spring 2001

March 15 Snow depth anomalies at Paradise, Mt Rainier

Avg ~ 4 meters (170 inches)January 5, 2005: 48 inchesJanuary 6, 2007: 130 inches

Avg=4 meters

Water Year Columbia River streamflow

Average annual runoff at The Dalles, Oregon ~ 150 Million Acre-Feet (MAF);

Oct 2000-September 2001 ~ 100 MAF

NW Climate variability

• Why the strong climate changes?– The chaotic nature of the climate system– big volcanic eruptions– natural modes of climate variability internal to

the climate system: • in the Pacific sector, changes in ENSO and PDO

are important factors

Oct 97-Mar 98:El Niño

Oct 98-Mar 99:La Niña

El Niño year precip anomalies Oct 1997- Mar 1998

La Niña year precip anomalies Oct 1998- Mar 1999

Regional patterns?

• Typically, cool-season (oct-mar) climate anomalies are coherent throughout most of the PNW region

• warm-season climate anomalies also tend to be regionally coherent, but to a lesser degree

Accumulated daily rainfall: Oct 1 1998-Sept 20 1999 A very wet year everywhere but Yakima!

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/current_impacts/global_precip_accum.html

“composite avg” PNW temperature and precipitation

during El Niño and La Niña

(based on averages of past century’s events)

EN-LN

The Pacific Decadal Oscillation

• an El Niño-like pattern of climate variability

• 20 to 30 year periods of persistence in North American and Pacific Basin climate

• warm extremes prevailed from 1925-46, and again from 1977-98; a prologed cold era spanned 1947-76

1998?1925 1947 1977

Mantua et al. 1997, BAMS

Real time “nowcasts” of the PDO?

http://jisao.washington.edu/pdo

Monthly PDO index: 1982-2010

Because we don’t know how the PDO works (key mechanisms for decadal patterns remain mysterious), we can’t be sure that the SST pattern (and PDO index) is a good indicator for where we are with this pattern. Recent years have a variable PDO index…

PDO and PNW monthly temperatures and precipitation

PDO and Cascades snowpack

0

100000

200000

300000

400000

500000

600000

700000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month

Average Flow (cfs)

ColdPDO

WarmPDO

Water year stream flow composites for Columbia River “natural” flows at The Dalles, Oregon

PDO/ENSO and NW hydrology

• Because extremes in ENSO and PDO tend to favor states of the Aleutian Low that favor either “warm and wet” or “cool and dry” conditions, these combinations lead to amplified responses in snowpack and streamflow – Ex: cold wet weather, lower snowline, more

precipitation, more snow, less evaporation and more runoff

Cool/Warm PDO and Paradise snowdepth histograms

Observed SST anomalies: Nov 14 - Dec 11, 2010

Degrees C

The Latest Climate forecasts from the International Research Institute for Climate Prediction

iri.colombia.edu

Recent La Niña Year snowpack

http://www.skimountaineer.com/CascadeSki/ParadiseCraterLakeSnow.php

1998-99



2000-01



2005-06

http://www.wcc.nrcs.usda.gov/snow/

This year

Last year

30 yr avg

northwest climate: the mean factors that influence local/regional climate: 1. latitude day length,...

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