Review of NCEP GFS Forecast Skills in 2011 and Beyond

Fanglin Yang

IMSG - Environmental Modeling Center National Centers for Environmental Prediction

Camp Springs, Maryland

The 46th CMOS Congress and the AMS 21th NWP and 25th WAF conferences, Montréal (Canada), May 29th to June 1st, 2012.

Acknowledgments: many scientists at NCEP and in the community have made contributions to the development and application of the GFS. For this presentation, I would like to thank in particular Joseph Sela, Moorthi Shrinivas, Hualu Pan, Stephen Lord, Bill Lapenta, John Derber, Mark Iredell, Glenn White, Russ Treadon, Mike Ek, Henry Juang, Yu-Tai Hou, Suru Saha, Bob Kistler, Jordan Alpert, Daryl Kleist, Jongil Han, Peter Caplan, Yuejian Zhu, Jun Wang, Helin Wei, Sarah Lu, Hui-Ya Chuang and others I am not be able to include here.

Annual Mean 500-hPa HGT Day-5 Anomaly Correlation

0.55

0.65

0.75

0.85 19

84

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

GFS-NH CDAS-NH GFS-SH CDAS-SH

In past 25 years GFS anomaly correlations increased by about 0.3 in both hemispheres (0.12/decade)

Annual Mean 500-hPa HGT Day-5 Anomaly Correlation

-0.1 -0.08 -0.06 -0.04 -0.02

0 0.02 0.04 0.06 0.08

0.1 0.12 0.14 0.16 0.18

0.2 19

84

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

NH:GFS-CDAS

SH:GFS-CDAS

Best Year, NH

Annual Mean NH 500hPa HGT Day-5 AC

0.6

0.65

0.7

0.75

0.8

0.85

0.9 19

84

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

GFS-NH CDAS-NH ECMWF-NH UKM-NH CMC-NH FNOMC-NH

• GFS falls behind ECMWF all the time. • GFS and UKMO were comparable for most of the time, but GFS trailed

UKMO in recent years. • FNOMC has made significant improvement since 2009.

2011 Annual Mean 500hPa HGT AC

5

• GFS falls behind EC and UK, but is better than CMC, FNO and JMA. • GFS useful forecasts (>0.6) reached 8.0 days in the NH and 7.8 days

in the SH.

NH SH

0.6 – useful forecast

Day at which forecast loses useful skill (AC=0.6) N. Hemisphere 500hPa height calendar year means

Fore

cast

day

8 d

Credit:, Peter Caplan, Yujian Zhu, Fanglin Yang

7

Twenty bins were used to count for the frequency distribution, with the 1st bin centered at 0.025 and the last been centered at 0.975. The width of each bin is 0.05.

Look at the history of extremes in the distribution

–Poor Forecasts (AC < 0.7 )

–Excellent forecasts ( AC > 0.9 )

Reduced poor forecasts

0

10

20

30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

%

8

Resolution: 1.2/2000:

T126L28 à T170L42 (70km)

2.11/2002: T170L42 à T254L64 (55km)

3.6/2005: T254L64 à T382L64 (38km)

4.7/2010: T382L64 à T574L64 (23km)

Percent of Poor Forecasts (AC <0.7) v.s. Model Changes

Physics and Data Assimilation:

A. 3/1999: AMSU-A &

HIRS-3 data

B. 5/2001: prognostic cloud water, cumulus momentum transport

C. 6/2005: OSU 2-L LSM to 4-L NOHA LSM

D. 5/2007: SSI to GSI; Hybrid sigma-p; New observations

E. 2/2009: flow-dependent error covariance; Variational QC

F. 7/2010: New shallow convection; updated SAS and PBL; positive-definite tracer transport.

G. 5/2011: GFS/GSI upgrade: new satellite data and thermal roughness

A

1

B

2

3, C 4, F

year

NH

1996 2011

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

%

9

Percent of Poor Forecasts (AC <0.7) v.s. Model Changes

A

1

B

2 3, C

4, F

year

SH

D

Physics and Data Assimilation:

A. 3/1999: AMSU-A &

HIRS-3 data

B. 5/2001: prognostic cloud water, cumulus momentum transport

C. 6/2005: OSU 2-L LSM to 4-L NOHA LSM

D. 5/2007: SSI to GSI; Hybrid sigma-p; New observations

E. 2/2009: flow-dependent error covariance; Variational QC

F. 7/2010: New shallow convection; updated SAS and PBL; positive-definite tracer transport.

G. 5/2011: GFS/GSI upgrade: new satellite data and thermal roughness.

E

Resolution: 1.2/2000:

T126L28 à T170L42 (70km)

2.11/2002: T170L42 à T254L64 (55km)

3.6/2005: T254L64 à T382L64 (38km)

4.7/2010: T382L64 à T574L64 (23km)

1996 2011

G

2011: A Year with Record-Breaking Billion-Dollar Weather Disasters

Hurricane Irene: 10 billion August 20-29, Cat 3 56 deaths

11

Hurricane Irene

GFS track forecast was one of the best

GFS

track intensity

GFS intensity forecast was also better than other global NWP models

GFS 60-84hr Rainfall Forecast: Hurricane Irene

24-hr rainfall, valid at 12Z28Aug2011

24-hr rainfall, valid at 12Z29Aug2011

0

50

100

150

200

250

300

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Trac

k Er

ror (

nm)

Atlantic Hurricane Track Errors 0

12

24

36

48

72

Forecast within 3 days has been steadily improving, although the pace is slow. Beyond day 3, forecast still varies from year to year.

Hurricane Track and Intensity Errors , GFS: 2001-2011

0

50

100

150

200

250

300

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Trac

k Er

ror (

nm)

Eastern Pacific Hurricane Track Errors 0

12

24

36

48

72

96

120 fhr

Recent and Upcoming Changes Hybrid-Ensemble Data Assimilation. Implemented on May 22nd, 2012. Semi-Lagrangian dynamics, T1148L64, still in development

16

T574L64 Hybrid Ensemble GFS Parallel

Tropical Wind RMSE, verified against ROBS

Global Temp RMSE, verified against RAOBS

17

Most Recent T1148L64 Semi-Lag GFS Test

Promising, but still has issues. Still testing different package options and tunable parameters.

Parallel run by Fanglin Yang on ESRL Jet

18

Extra slides

Annual Mean SH 500hPa HGT Day-5 AC

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9 19

84

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

GFS-SH CDAS-SH ECMWF-SH UKM-SH CMC-SH FNOMC-SH

20

Tropical Wind RMSE, 850-hPa Day-3 Forecast

July2010 T574 GFS Implementation

GFS tied with EC and UK after July 2010 implementation.

21

Tropical Wind RMSE, 200-hPa Day-3 Forecast

• GFS has larger wind RMSE than EC and UK at the tropopause region.

• Improvement in the past 15 years is not significant.

22

Twenty bins were used to count for the frequency distribution, with the 1st bin centered at 0.025 and the last been centered at 0.975. The width of each bin is 0.05.

Look at the history of extremes in the distribution

–Poor Forecasts (AC < 0.7 )

–Excellent forecasts ( AC > 0.9 )

Hurricane Track and Intensity Errors

23 AVNO = GFS EMX = ECMWF 00Z and 12Z cycles

2011 Atlantic 2011 Atlantic

10

20

30

40

50

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Inte

nsity

Err

or (k

ts)

Atlantic Hurricane Intensity Errors 0

12

24

36

48

72

96

120 (fhr)

CONUS Precipitation, 0-72hr Total

25

2011 CONUS Precipitation Skill Scores

26

T574L64 Hybrid Ensemble GFS

The parallel outperformed operational GFS in both NH and SH.

NH SH

27

Percent of Excellent Forecasts (AC >0.9)

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

%

Year

Percent Anomaly Correlations Greater Than 0.9 GFS 00Z Cycle Day-5 500hPa Height

NH SH

1996 2001 2000 1998 1997 1999 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

2011 Hurricane Track and Intensity Forecast Errors

2011 Atlantic Hurricanes

2011 Eastern Pacific Hurricanes

http://www.wikipedia.org

2011 Eastern Pacific Hurricane Track and Intensity Errors

29 AVNO = GFS EMX = ECMWF 00Z and 12Z cycles

2011 Western Pacific Hurricane Track and Intensity Errors

30 AVNO = GFS EMX = ECMWF 00Z and 12Z cycles