From Drought to Flood

FMA Annual Meeting 2017

Dr. Michael Anderson, State Climatologist

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California Statewide 4-yearPrecipitation Sum4-yearPrecipitation Sum

Year 4-year sum2015 62.21920 63.01926 63.31931 64.41934 65.1

Lowest Totals

Average:85.9 inches

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Annual Average Temperature (deg F)

Climate Division 2 (Sacramento Basin) – Calendar Year Data

1895-2000 21st Century POR Average

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Sierra Winter (DJF) Average Minimum Temperature (degrees Fahrenheit)

SierraRegion

9 Years Below 50%

Snowpack and Winter Temperatures of the Sierra Nevada

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2017

Distribution of Landfalling Atmospheric Rivers on the U.S. West Coast (From 1 Oct 2016 to 12 April 2017)

Ralph/CW3E AR Strength Scale• Weak: IVT=250–500 kg m–1 s–1

• Moderate: IVT=500–750 kg m–1 s–1

• Strong: IVT=750–1000 kg m–1 s–1

• Extreme: IVT>1000 kg m–1 s–1

AR Strength AR Count*

Weak 12

Moderate 21

Strong 13

Extreme 3

• 49 Atmospheric Rivers have made landfall on the West Coast thus far during the 2017 water year (1 Oct. – 12 April 2017)

• This is much greater than normal • 1/3 of the landfalling ARs have been “strong” or “extreme”

*Radiosondes at Bodega Bay, CA indicated the 10–11 Jan AR was strong (noted as moderate based on GFS analysis data) and 7–8 Feb AR was extreme (noted as strong)

By F.M. Ralph, B. Kawzenuk, C. Hecht, J. KalanskyCenter for Western Weather and Water ExtremesScripps Institution of Oceanography

Water year 2017 AR landfall

locations through 11 April 2017

Location of landfall represents position where AR was strongest at landfall . Many ARs move down the coast over time. This map does not show these areas.

Magnitude DurationBetween

Clustering

FreezingElevation

From Ben Hatchett, WRCC, UNR

12”

18”

26”31”5750’

EventDuration

Seasonal Outlook for Water Year 2018

Storm Track changes

Flooding & water supply

MJO/Tropical Convection ENSO

Polar Processes

Key Phenomena Affecting California Water Supply/Flooding:

Easterly Wave

CyclogensisL

The size, number, and strength of atmospheric river events (ARs) result from the alignment of key

physical processes operating on different space and time scales that will change with climate change

Circulation Patterns of Note

IRI/CPC Pacific Niño 3.4 SST Model Outlook

Figure provided by the International Research Institute (IRI) for Climate and Society (updated 18 August 2017).

Most models and the multi-model averages predict ENSO-Neutral through the remainder of the year and into early 2018.

From Climate Prediction Center’s ENSO Diagnostic Discussion

U. S. Seasonal Outlooks

Precipitation Temperature

September – November 2017

The seasonal outlooks combine the effects of long-term trends, soil moisture, and, when appropriate, ENSO.

Signposts for the Seasons

• Fall – Heat and/or decaying tropicals?

• Winter – Will the circulation align for a cluster of ARs once or twice?

• Spring – Early shutdown?

• Can you have a flood and a below average water year?