La Niña impacts on Pacific Northwest climate in spring:
2011 and the historical record
Jim Johnstone
JISAO-UW
[email protected]
Niño 3.4 index
SST anomalies
January 3, 2011
Sea-level pressure (SLP) anomalies
March 2011
SOI
Niño 3.4 index
SOI
Feb-Apr SOI
Strongest spring La Niña on record (to 1866)
Lowest Apr-Jun Tmax in WA (to 1900)
Pac NW Precip
Pac NW Tmax
Airport cloud ceilings(hours per day)
SeaTac
Airport cloud ceilings(hours per day)
SeaTac
Portland
US Tmax anomalies
Apr-Jun 2011
Record values
(back to 1951)
2011 monthly 500 mb anomalies (i.e. pressure)
Feb
Mar
Apr
May
Jun
Jul
April-Jun 500 mb anomalies
Strong La Niña that persisted into April
Persistent and strong anomalies over the Pacific NW (and beyond) through June
Cause and effect?
Do Feb-Apr La Niña conditions occur with Apr-Jun anomalies over the Pacific NW?
Composite La Niña (Top 10)
Dec-Feb 500 mb
Composite La Niña (Top 10)
Dec-Feb 500 mb
Winter La Niña composites (Dec-Feb)
Precip
Tmax
La Nina winter composite
2011 Apr-Jun
Composite La Niña (Top 10)
Feb-Apr 500 mb
Composite La Niña (Top 10)
(Feb-Apr) Feb-Apr
Mar-May
Apr-Jun
500 mb
Tmax
Apr-Jun 2011
Apr-Jun response to Feb-Apr La Niña
Composite La Niña (Top 10)
(Feb-Apr) Feb-Apr
Mar-May
Apr-Jun
Tmax
500 mb anomalies Apr-Jun 2011
Conclusion:
Apr-Jun climate patterns similar to a typical La Niña pattern(Trough PNW, Ridge SE)
But historical data shows limited effects of La Niña in spring
La Niña US tornadoes
Spring (MAM) Z500 composite anomalies (normalized)