Is Eurasian snow cover in October a reliable statistical

5 In this study, the recently found lead-lag relationship between Eurasian snow cover 6 increase in October and wintertime precipitation totals on the Iberian Peninsula is re7 visited and generalized to a broad range of atmospheric variables on the synoptic and 8 local scale. To this aim, a robust (resistant to outliers) method for calculating the index 9 value for Eurasian snow cover increase in October is proposed. This ‘Robust Snow 10 Advance Index’ (RSAI) is positively correlated with the wintertime (DJF) frequency 11 of cyclonic and westerly-flow circulation types over the Iberian Peninsula, while the 12 corresponding relationship with anticyclonic and easterly-flow types is negative. For 13 both cases, an explained variance of ∼ 60% indicates a strong and highly significant 14 statistical link on the synoptic scale. 15 Consistent with these findings, it is then shown that the lead-lag relationship equally 16 holds for the DJF-mean conditions of 1) precipitation amount, 2) diurnal temperature 17 range, 3) sun hours, 4) cloud cover, and 5) wind speed on the local scale. To assess if 18 these target variables can be skillfully hindcasted, simple linear regression is applied 19 as a statistical forecasting method, using the October RSAI as the only predictor vari20 able. One-year out cross-validation yields locally significant hindcast correlations of 21 up to ∼ 0.8, obtaining field significance for any of the five target variables mentioned 22 above. The validity for a wide range of atmospheric variables and the consistency of 23 the localand synoptic-scale results affirm the question posed in the title. 24