Jet Propulsion Laboratory California Institute of Technology

Progress in Subseasonal Weather/Climate Forecasting Duane Waliser Jet Propulsion Laboratory/Caltech Pasadena, CA

Drought Response Workshop February 25-26, 2015 Irvine, CA

Weather Forecasts ~ O (10 Days) (Mid-Latitude Baroclinic Instability & Cyclone Lifetime)

Dynamic Forecasts root back to 1910

What about the forecasting between “weather” & climate ~ 2 weeks to 2 months? (aka sub/intra – seasonal)

Seasonal Forecasts ~ O (100 Days) (ENSO phenomena & Local/Remote Circulation Impacts)

Dynamic Forecasts root back to Mid1980’s

Progress and Importance in “ISI” Prediction Warranted a 2010 National Research Council Study ISI = Intraseasonal to Interannual aka S2S = Subseasonal to Seasonal

Useful predictions depend on having and being able to model “sources of predictability” with time scales that exceed typical weather patterns • • • • • •

El Nino – Southern Oscillation (ENSO) Madden-Julian Oscillation (MJO) Soil Moisture & Snow Cover Sea Ice Stratosphere–Troposphere Interaction Other slow ocean & atmosphere “waves” e.g. PNA, AO, IOD, CCEWs

Madden-Julian Oscillation

B&W “Photo” of whole tropics every 6 days

Madden & Julian, 1972

We have a Daily Index of MJO Activity Since 1979 Wheeler & Hendon 2004

Every day the MJO is characterized by a Phase (1-8) & Amplitude

Multi-week Insight into Monsoon Onsets & Breaks

Two Examples of Why Accurate MJO Forecasts Would be of Exceptional Value Multi-week Insight into Tropical Cyclone Frequency

Summer

MJO & Tropical Cyclones MJO Enhancement

MJO Suppression

1949-97 Tropical Storms & Hurricanes

Westerly/ Cyclonic Phase Higgins et al. 2000

Maloney and Hartmann, 2000

Easterly/ AntiCyclonic Phase

MJO Modulation of US (Dec-Feb) Temperature Anomalies Zhou et al. 2012

MJO Modulation of CA Winter Precipitation Seasonal Precipitation Rates ~2-4 mm/day MJO Modulation ~ +/- 1 mm/day Predictability Value!

Courtesy B. Guan/UCLA

The MJO & CA Winter Precipitation Typical Impact of MJO on California Precipitation Phase 1

Phase 5

Typical CA Wintertime Precipitation Rates ~2-4 mm/day (not shown); MJO Modulation ~ +/- 1 mm/day (~25-50%)

Left Figure CLIVAR MJO Working Group Right Figure Courtesy B.Guan, JPL/UCLA

MJO Occurrence and Frequency Jones et al. 2012

A few events per year – providing “forecasts of opportunity”

MJO Prediction Evolution

1990

2000

2010

Late 1990’s – Early 2000’s

• Operational MJO forecasts didn’t exist. • Focus on El Nino and Seasonal Forecasting • Weather and climate prediction models had poor representations of the MJO • MJO forecasts only good to a few days

Assessment of Intraseasonal to Interannual (ISI) Climate Prediction and Predictability, NRC 2010

See recent review Waliser, 2011

MJO Model and Forecast Improvement from the European Center for Medium Range Weather Forecasting (ECMWF) OLR; 15-day Lead Time; 10N-10S; TOGA COARE

Courtesy F. Vitart ECMWF

Promising gains from continued model improvements Resolution, Data Assimilation, Model Physics (Tomkins et al. 2007; Bechtold et al 2008) – M. Miller.

MJO Model and Forecast Improvement from the European Center for Medium Range Weather Forecasting (ECMWF) OLR; 15-day Lead Time; 10N-10S; TOGA COARE

Courtesy F. Vitart ECMWF

Promising gains from continued model improvements Resolution, Data Assimilation, Model Physics (Tomkins et al. 2007; Bechtold et al 2008) – M. Miller.

80 ensemble mean start dates, daily 1st Feb., May, Aug and Nov 1989-2008

Courtesy, F. Vitart ECMWF

MJO Forecasts from ECMWF

Useful MJO prediction skill out to 4+ weeks!

Progress attributed to • • •

better models more/better observations for initial conditions more computer power

Operational MJO Forecasts Many operational weather prediction centers now routinely produce MJO predictions

Gottschalck et al. BAMS, 2010

10 operation centers, 20 data streams, 13 ensemble forecasts (with 4 – 51 members)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml

Operational MJO Forecasts Prediction of a strong MJO event

NCEP

ECMWF

UKMO

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml

Operational MJO Forecasts The MJO represents a “forecast of opportunity”

This week

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml

NOAA Global Tropics Hazards & Benefits Outlook

Based in part on MJO forecasts

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/

Subseasonal Forecasting Atmospheric Rivers?

ARs : Key to Beneficial & Hazardous Water Delivery

ARs Provide beneficial rain and snow for water supply

25% - 45% of annual precipitation in the west coast states fell in association with atmospheric rivers

Atmospheric Rivers are to the west what Hurricane Hazards are to the Southeast

From Dettinger et al. in Water, 2011

Ralph & Dettinger, 2012 An average AR transports the equivalent of 7.5 times the average discharge of the Mississippi River, or about 10 Million acre feet 22 per day. Of this, 20-40% may become precipitation.

Forecast Models Need to Improve their Forecasts of Landfall Location For example: at 5-6 day lead time, global weather forecasts cannot determine if it will hit LA or San Francisco

RMS Error in Forecast AR Landfall Location

Wick et al. 2013

The Unusually Snowy Winter of 2010/2011

2010/2011 winter • Largest total seasonal snow (~170% above normal) • Largest number of AR dates (twice normal) • Largest AR-related snow accumulation

On average 9 AR dates per winter contribute 37% total snow

December 18 to 22 – Five Straight Days of AR 17–19 December 2013

20–22 December 2013

• >13 feet of snow in the Sierras • >6 inches of rain in LA and >21 inches in parts of the foothills • Spread into Nevada/Arizona/Utah ; Zion NP evacuated

14 out of the season’s 20 AR dates occurred in one month

* No. of ARs in Dec. 2010 well above normal range

Right: Ralph and Dettinger 2012,

Climate Conditions of the 2010/2011 Winter –AO and –PNA tend to be associated with more stormy weather in California

500 mb Geopotential Height Anomalies

“Arctic Oscillation” (AO)

“Pacific North American” (PNA)

Circulation anomaly when both PNA and AO in “negative” phase

Phasing of AO/PNA vs. AR Frequency in California

When the AO and PNA are both in the negative phase, ARs are significantly more likely to occur.

Does the MJO influence ARs? A Little Bit More high-impact ARs are observed during MJO phase 6 – convection in the W. Pacific Ocean, including the top two events during WY1998-2010.

Guan, B., et al. 2012 AR events during WY 1998-2010 are plotted in relation to the phase and amplitude of the MJO. The amplitude of the AR is shown in terms of DSWE as size of green circles. AR dots/events inside the unit circle occur during weak/no MJO. AR dots/events outside unit circle occur during strong MJO events in the given phase of the MJO life-cycle.

New National Research Council Study “Developing a U.S. Research Agenda to Advance S2S Forecasting” S2S = Subseasonal to Seasonal

Recommend a bold strategy to increase the nation's scientific capacity for research on S2S forecasting • • • • • •

sources of predictability process studies & improving models sustained and new observations uncertainty quantification communication & decision support computation & infrastructure

Subseasonal to Seasonal (S2S) Project An International Experimental Operational Forecast Activity

Targets improving accuracy and use of forecasts at lead times of 2 weeks to 2 months

WMO Bulletin

S2Sprediction.net

• • • • •

5 – year project, starting 2014 11 operational forecast centers database of ~45 day forecasts focus on science & applications learn to tailor forecast products

Summary • Subseasonal (e.g. MJO) forecasting has become operational and starting to be useful – great progress in last 5-10 years. • MJO impacts on west coast wintertime precipitation and snowpack are evident and to some extent becoming predictable and lead-times of order weeks. • Significant community activities working towards improving global weather/climate model representation of the subseasonal phenomena (e.g. MJO, sea ice, soil moisture) to improve subseasonal predictions. • This work is really just beginning, and more “R” as well as “R2O” is needed before these sorts of relationships and their predictability can be “O”perationally exploited for weather and water related decision support.

• The S2S Project and the US NRC Study on S2S are poised to help improve the accuracy and utilization of S2S forecasts.