# Presentation: 670346

## MARCH 2004 UPGRADE OF THE NCEP GLOBAL ENSEMBLE FORECAST SYSTEM

***Zoltan Toth***
***Yuejian Zhu***
***Richard Wobus***
**Environmental Modeling Center**
**NOAA/NWS/NCEP**
- Acknowledgements:
- David Michaud, Yuqiu Zhu	NCO
- Hua-Lu Pan, Steve Lord		EMC
*http://wwwt.emc.ncep.noaa.gov/gmb/ens/index.html*

## NCEP GLOBAL ENSEMBLE FORECAST SYSTEM

**NCEP GLOBAL ENSEMBLE FORECAST SYSTEM**

- CURRENT SYSTEM

- NEW CONFIGURATION
- MARCH 2004

- RECENT UPGRADE (Apr. 2003)

- 10/50/60% reduction
- in initial perturbation size over NH/TR/SH

## 1.  Extend T126 portion of forecast from 84 to 180 hours

- 2.  Run 4 cycles per day, adding 06Z and 18Z forecasts

- 3.  Extend out to 180 hrs the high resolution enspost and ensstat
-  files, and add new precipitation-related enspost and ensstat files

- 4.  Shorten the time step for the T126 part of the forecast

## 1.  Extend T126 portion of forecast from 84 to 180 hours

-  This change is intended to improve ensemble support for
-  4-7 day forecasting, to allow tropical cyclone tracking
-  out to 7 days, and to provide boundary conditions for
-  SREF out to 90 hours
-  *Rusults:*
*	**More realistic forecast patterns between 84-180 hrs*
*	**Improved skill beyond 84 hours*
*	**Increased spread in 4-10 days period, better reliability*

**PLANNED CHANGES - 1**

## 2.  Run 4 cycles per day, adding 06Z and 18Z forecasts

-  This change provides more timely information,
-  corresponding to the 4 GFS control forecasts each day, and provides
-  more ensemble members to contribute to medium-range and week-2
-  forecasts
*Results:*
* **The new cycles increase the information content*
* **and utility of ensemble-based products*

**PLANNED CHANGES - 2**

## improved enspost & ensstat output information

**a)****	****Extend out to 180 hrs the high resolution (1x1) files**
**Increase frequency of ensemble output from 12- to 6-hrly **
**Add precipitation type information**
-  These changes improve ensemble support for
-  medium-range and week-2 weather forecasting
*Results:*
*Utility of ensemble forecast data enhanced*

**PLANNED CHANGES - 3**

## 4.  Shorten the time step for the T126 part of the forecasts

-  This change is intended to improve the quality of the ensemble
-  forecasts by using the same 10 min time step as used in the GFS control
- instead of the longer (20 min) step that had been used in the ensemble
*Results:*
*This change improves the quality of the high resolution T126 portion of the ensemble forecasts that, in certain flow situations, has been degraded by the use of the longer time step. Occasional poor ensemble performance related to time step problem is eliminated*

**PLANNED CHANGES - 4**

## RMS ERROR, ENSEMBLE SPREAD, OUTLIER STATISTICS, NH

**RMS ERROR, ENSEMBLE SPREAD, OUTLIER STATISTICS, NH**

- RMS error slightly reduced
- Ensemble spread significantly  increased

- Number of cases when ensemble misses verification significantly reduced

*RESULTS BASED ON 29-DAY NCO PARALLEL TESTING*

## PATTERN ANOMALY CORREL, RANKED PROBABILITY SKILL SCORE, NH

**PATTERN ANOMALY CORREL, RANKED PROBABILITY SKILL SCORE, NH**

- PAC slightly improved

- Probabilistic skill scores improve by 0.5 day around day 7 lead time

## PAC FOR SH, BRIER SKILL SCORE FOR TROPICS

**PAC FOR SH, BRIER SKILL SCORE FOR TROPICS**

- Performance improves over SH extratropics as well

- Both reliability and resolution components of probabilistic performance improves over the tropics

## OR

- Increase resolution
- Horizontal
- Vertical
- Use better physics

*Run more members*
- Increase membership
- Run ens. more often

- How do we evaluate test results?
- Answer will depend on user procedures
- Evaluate before or after statistical post-processing
- Effect of bias correction, smoothing, inter- and extrapolation etc can be crucial
- Multifaceted problem, scientific results, user input, all need careful consideration
- Trade-off

*Make reforecast runs*
- For improved post-processing

**HOW TO BEST UTILIZE INCREASED COMPPUTING POWER IN FUTURE?**

*Whitaker and Hamill, 2004*

*Toth & Kalnay, 1997*

*Wei & Toth, 2003*

*Mullen & Buizza, 2002l*

## Test effect of doubling membership

- Still over somewhat steep curve regarding potential gain
- 5% detection level for highly nonlinear aspects of forecast
- For more linear aspects, extrapolation gives good probabilistic resolution
- Can help with ET applications
- Rescaling for generating initial perturbations
- Targeted observation applications
- Can be combined with MSC & other ensembles in future to gain 100+ members
- Increase resolution?
- For first 84 hrs from T126 to T170?
- Vertical resolution from 28 to 64 levels?
- Coupled ocean-atm model uses T62-L64 version
- For 2nd week, from T62 to T126?
- Keep room for operational generation of
- 		reforecast data for next configuration?
- Use two-tier approach?
- Update model used for 1st week semi-annually
- Update only every 3 yrs for 2nd week?

**NCEP PLANS**

*Whitaker and Hamill*