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Christopher M. Rozoff and James P. Kossin

independent testing methods, dependent testing will inflate measures of skill, and a comparison of model biases (as discussed above) is not as meaningful, but the dependent analysis is adequate for the purpose of comparing the relative performances of the three models and their ensemble mean. Figure 5 compares the BSS computed from the dependent dataset for each model and the three-model ensemble-mean forecast. The logistic regression model possesses higher forecast skill than does the Bayesian model

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Agostino Manzato

superior to the skill scores of the Renick and Maxwell (1977) method when applied to the same dataset. Apart from these physical methods, purely statistical models were also developed. An example is the multivariate statistical approach given by López et al. (2007) , which developed a short-term hail occurrence forecast from sounding-derived indices, using a logistic-regression approach. Starting from 22 candidate indices, López et al. selected a set of seven variables, including instability (total

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M. Bessafi, A. Lasserre-Bigorry, C. J. Neumann, F. Pignolet-Tardan, D. Payet, and M. Lee-Ching-Ken

Modèle Climatologiques de Cyclones par Analogues (MOCCANA). The same version can be used anywhere among all the tropical cyclone basins. The regression equations are developed using principal component analysis (PCA). The type of predictors and predictands entering the model, the analog selection process, and the derived regression equations are introduced in Section 2 . The analysis of the analog processing in the seven major ocean basins is outlined in section 3 , and results for a CLIPER and

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William E. Togstad, Jonathan M. Davies, Sarah J. Corfidi, David R. Bright, and Andrew R. Dean

explore the possibility that useful logistic regression models might be developed for assessing the conditional probability of significant (EF2 or stronger) tornadoes when environmental background parameters such as those described in earlier work (e.g., T03 , R03 , D04 , T07 ) are applied as independent variables. It should be noted that because the database utilized for regression equation development was entirely composed of RUC analysis soundings in proximity to observed supercell

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Robert Fawcett

of LEPS2SS (vertical axis) against PCSS (horizontal axis) for the two-category linear regression model (thick solid line), the two-category linear discriminant analysis model (thick dashed line) and the degraded unreliable version (thin dotted line), and the two-category stratified climatology model (thick dashed line). Fig . 8. Comparison of the relationships between PCSS and each of LEPS2SS, PICSS, BS1SS, and BS2SS for the three-category LR (solid lines) and LDA (dashed lines) models. Fig . 9

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Dennis Chesters, Anthony Mostek, and Dennis A. Keyser

are much weaker. This study with the 20 July case validates that VASsounding images are a reliable tool for dependent casestudy analysis (i.e., where the retrievals are made witha regression matrix trained in the same region of spaceand time).c. Independent validation study Stability parameters are retrieved from 20 July observations using the 13 July regression matrix to testthe method with independent statistics. Operationally,one could make regular synoptic updates of the VASregression

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Xianmei Lang and Huijun Wang

the extraseasonal numerical predictions for summer climate but are statistically significant when correlated with the regional summer rainfall in China. Following this, regression analysis was used to construct statistical prediction models of summer rainfall for the regions of concern, based on both the precursory climate signals and the synchronous numerical prediction results. To improve the accuracy of the predictions, systematic errors between predictions and observations in recent years were

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Kevin M. Simmons and Daniel Sutter

verification statistics ( Polger et al. 1994 ; Bieringer and Ray 1996 ), but employed warning statistics from only six WFOs and only for less than 10 yr. We use a dataset of all tornadoes in the contiguous United States between 1986 and 1999, consisting of nearly 15 000 tornadoes. We also examine the impact of WSR-88D installation on tornado casualties. We offer a test of whether tornadoes produce fewer casualties after WSR-88D installation in a regression analysis of tornado casualties. We include

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Rodney A. Donavon and Karl A. Jungbluth

. After the 50-dB Z echo height was evaluated and an MLT was determined for each report, the data were plotted on a scatter chart for further analysis. 3. Results A preliminary linear comparison was conducted to determine whether the depth of the MLT, or the height of the wet-bulb zero, had a stronger linear relationship with the height of the 50-dB Z echo for severe-sized hail. A dataset containing 83 reports of hail 19–25 mm in diameter was used to complete the linear regression. Results for the

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Sim D. Aberson

the predictability timescale found in this study. The discrepancy may be due in part to the difference in the definitions of skill and error, since forecasts with very large errors may be skillful if the CLIPER forecast errors are even larger. 4. Regression analysis and choice of predictors Two different statistical track models for the Atlantic basin have been derived for 3-day forecasts, one for the Atlantic ( Neumann 1972 ) and one for the Gulf of Mexico ( Merrill 1980 ). After the Merrill

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