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 winds and pressure over the North Pacific Summer winds and pressure over the North Pacific “Aleutian Low” “Subtropical High” H H L L

Oregon Climate Service

Northwest terrain maps the big-picture winds and storms onto a complex landscape localized cold air outbreaks the Puget Sound Convergence Zone rain shadows

“Arctic Blasts”

The Puget Sound Convergence Zone

Annual average rain+snowfall:

The predictable part: seasonal rhythms Puget Sound Precip Upwelling winds at 48N Amphitrite Pt SST Oct Feb Jun Jan May Sep Insolation

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 Local and regional vegetation change on the northeastern Olympic Peninsula during the Holocene. Canadian J. of Botany. alder cedars pines df

Source: Gedalof, Z., D.L. Peterson and Nathan J. Mantua. (2004). Columbia River Flow and Drought Since Journal of the American Water Resources Association. The Dust Bowl ( ) was probably not the worst drought sequence in the past 250 years (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 Washington State Oct-Sept Total Precip

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 inches January 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 Mar 1998 La Niña year precip anomalies Oct 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 Sept A very wet year everywhere but Yakima!

“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 , and again from ; a prologed cold era spanned ? Mantua et al. 1997, BAMS

Real time “nowcasts” of the PDO? Monthly PDO index: 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

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 now.php

Recent La Niña Year snowpack now.php

Recent La Niña Year snowpack

This year Last year 30 yr avg