1. Assessment of the NCEP CFS Hindcast Runs on Predicting the North American Monsoon
Lindsey Long and Jae Schemm
NOAA/NWS/NCEP/CPC
Runs courtesy of Suranjana Saha
NOAA/NWS/NCEP/EMC

2. Introduction Focus on Precipitation and Atmospheric Circulation
Look at both seasonal and interannual variability
Five varying runs allow us to look at the affect of:
Lead Time
Updates to the CFS model
Horizontal Resolution

3. Description of Runs 5 different hindcast runs from 1981-2006
Two 15-member ensemble mean hindcasts from current operational CFS
1-month lead (May)
3-month lead (March)
Three single runs with differing horizontal resolutions using an updated CFS
T62
T126
T382

4. Summary of Runs Run CFS Version Resolution Initial Condition # of Runs1
GFS 2007 / MOM3
T382
May 15th
Single 2
T126 3
T62 4
Operational
May
15-Member Ensemble Mean 5
March
15-Member
Ensemble Mean

5. Complex Terrain Demonstrates the need for finer horizontal resolution
Gulf of
California
Sierra Madre
Occidental
Mexico
Baja
Do a quick overview of the topography of the NAM area.

6. NAME Sub Regions
TIER 1.5
CORE
AZNM
Arizona/New Mexico Region (AZNM) ; (Higgins et al. 1998)
CORE Region (Gutzler 2004)
Tier 1.5 Region (NAMAP2)
Define regions

7. CFS JJAS Precipitation [cm], 1981-2006
URD (1x1) T T126
T Oper T62 May Ensm Oper T62 March Ensm
Make sure to mention obs=Unified Rain gauge Dataset

8. CFS JJAS Precipitation Model Minus Obs [cm], 1981-2006
URD (1x1) T T126
T Oper T62 May Ensm Oper T62 March Ensm
Model Bias – start with T62 operational. Discuss how operational is doing. Then T62 new = still has dry bias but precipitation starting to organize along mountain region. Then T126 and T382 have wet bias.

9. Seasonal Cycle of Precipitation
a) AZNM
CORE Region shows good example of increased accuracy with resolution and model upgrade
TIER 1.5 shows less improvement with new model runs
b) CORE
c) TIER 1.5
URD T T T62
T62
May
T62
March

10. Seasonal Cycle of Precipitation
a) AZNM
CORE Region shows good example of increased accuracy with resolution and model upgrade
TIER 1.5 shows less improvement with new model runs
In all regions, T382 run does well capturing monsoon onset (June-July)
b) CORE
c) TIER 1.5
URD T T T62
T62
May
T62
March

11. CFS Diurnal Cycle of Precipitation JJAS (mm/day)
AZNM
CORE
South East
Great Plains
Mountain
CFS Diurnal Cycle of Precipitation JJAS (mm/day) l
T62
T126
T382
NARR
Note NARR used since need 3-hrly

12. Interannual Variability
a) AZNM
b) CORE
Anomalous Precipitation for JJAS
c) TIER 1.5
Because these are so noisy lets look at the correlations instead. Also, mention that show hint of decadal trend.
URD T T T62
T62
May
T62
March

13. Interannual Variability
a) AZNM
b) CORE
Anomalous Precipitation for JJAS
Decadal Trend present in observations and CFS
c) TIER 1.5
Because these are so noisy lets look at the correlations instead. Also, mention that show hint of decadal trend.
URD T T T62
T62
May
T62
March

14. Precipitation Correlations to URD
a) AZNM Monthly
d) AZNM Seasonal
b) CORE Monthly
e) CORE Seasonal
c) TIER 1.5 Monthly
f) TIER 1.5 Seasonal
T382 doing best in the AZNM region, but in larger regions T126 doing better. Top correlation = 0.51 in Aug Tier 1.5 by T126
T T T62
T62
May
T62
March

15. Atmospheric Circulation
Prominent upper-air features in the NAME region:
Anticyclonic flow over the region
Low-level jet over the Gulf of Mexico
Low-level jet over the Gulf of California

16. Atmospheric Circulation (JJA)
300 mb Streamlines, 850 mb Wind Vectors
NARR T T126
T Oper T62 May Ensm Oper T62 March Ensm
Show both JJA and JAS because of large change between seasonal averages – anticyclone flow in JJA T382 run disappears in JAS and appears in operational ensms. Still in wrong position though.

17. Atmospheric Circulation (JAS)
300 mb Streamlines, 850 mb Wind Vectors
NARR T T126
T Oper T62 May Ensm Oper T62 March Ensm

18. Gulf of California LLJ, 850 mb Winds
Strong Southerly Flow
Weak Westerly Flow
NARR
T382
Note that NARR southerly flow may be too strong, but still flow is directionally correct.

19. Conclusions
As expected with the complex terrain of the NAMS, increased resolution does improve the precipitation forecast.
Correlations show Interannual Variability is improving with resolution
Improvement also seen at the Seasonal and Diurnal time scales.
Comparisons of the T62 runs highlight the improvement provided by the updated atmospheric GCM model.
Change in lead time for Ensemble Mean hindcasts show only a slight improvement in May versus March
The general circulation is still a problem area.
Missing anticyclonic flow over the monsoon area
Lacking the southerly flow associated with the LLJ; therefore, the warm moisture brought into the region by this jet is missing.

20. Thank you! Questions?