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COSMO-LEPS Verification
Chiara Marsigli ARPA-SMR
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Available italian stations
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Verification on station points
Bi-linear interpolation (4 nearest points) X
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Verification on super-boxes
Average value – maximum value – frequency OBS. PRED. X
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OVERLAPPING BOXES X X X X
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ROC area Need for LM verification at these fc ranges COSMO-LEPS vs
observations station points weighted Need for LM verification at these fc ranges ROC area Nov 02 – Dec 02 – Jan 03
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COSMO-LEPS vs observations station points not weighted ROC area
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w +48 h nw
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w +120 h nw
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COSMO-LEPS vs observations station points weighted Brier Skill Score
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Brier Skill Score COSMO-LEPS vs observations station points
not weighted Brier Skill Score
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Brier Skill Score
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Weighting procedure It is possible to decide (in real-time)
if it is better to weight or not to weight? Dependence from ensemble spread? Flow dependence?
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Brier Skill Score station points average values on super-boxes
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Brier Skill Score station points average values on super-boxes
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Brier Skill Score Nov 02 only
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Brier Skill Score
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ROC area contingency table Observed Yes No Forecast a b c d
A contingency table can be built for each probability class (a probability class can be defined as the % of ensemble elements which actually forecast a given event). For the k-th probability class: The area under the ROC curve is used as a statistic measure of forecast usefulness
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Brier Skill Score oi = 1 if the event occurs
Brier Score oi = 1 if the event occurs = 0 if the event does not occur fi is the probability of occurrence according to the forecast system (e.g. the fraction of ensemble members forecasting the event) BS can take on values in the range [0,1], a perfect forecast having BS = 0 The forecast system has predictive skill if BSS is positive, a perfect system having BSS = 1. Brier Skill Score = total frequency of the event (sample climatology)
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