Title: LOOKING BEYOND THE FIRST TWO MOMENTS IN ENSEMBLEBASED PROBABILISTIC FORECASTS
1LOOKING BEYOND THE FIRST TWO MOMENTS IN
ENSEMBLE-BASED PROBABILISTIC FORECASTS
- Zoltan Toth
- Environmental Modeling Center
- NOAA/NWS/NCEP,
- Yuejian Zhu, Dingchen Hou(1), Ervin Zsoter(2)
- (1) SAIC at NCEP/EMC, Washington, US
(www.emc.ncep.noaa.gov) - (2) Hungarian Meteorological Service
- http//wwwt.emc.ncep.noaa.gov/gmb/ens/index.html
2OUTLINE / SUMMARY
- FORECAST ATTRIBUTES
- Reliability - Can be statistically corrected
- Resolution - Can be improved, but not
corrected statistically - VARIATIONS IN FORECAST UNCERTAINTY
- Probability associated with mode of fcst
distribution varies - Ensemble can capture variations in fcst
uncertainty - BI- AND MULTIMODALITY
- Composite distributions according to their
max/min - Details in ensemble pdf seem to correspond with
distribution of verifying observs.
3ATTRIBUTES OF FORECASTS
RELIABILITY Lack of systematic error (No
conditional bias) CAN BE statistically
corrected (assuming stationary processes)
RESOLUTION Different fcsts precede
different observations CANNOT be
statistically corrected - INTRINSIC VALUE OF FCST
SYSTEM
For perfectly reliable fcsts, resolution
ensemble spread spread in observations
gt Perfect predictability only 0 100
probabilities used, and always correct No
predictability No matter what we forecast,
climate distribution is observed
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5PROBABILISTIC FORECASTING Based on SINGLE
FORECAST One integration with an NWP model,
combined with past verification statistics
- Does not contain all forecast information
- Not best estimate for future evolution of system
- UNCERTAINTY CAPTURED IN TIME AVERATE SENSE -
- NO ESTIMATE OF CASE DEPENDENT VARIATIONS IN FCST
UNCERTAINTY
6- INITIAL CONDITION RELATED ERRORS
- Sample initial errors
- Run ensemble of forecasts
- Can flow dependent variations in forecast
uncertainty be captured? - May be difficult or impossible to reproduce with
statistical methods
7Full ensemble pdf
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11144 hr forecast
Poorly predictable large scale wave Eastern
Pacific Western US
Highly predictable small scale wave Eastern US
Verification
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