Daily Analyses. A series of t-tests were employed to determine if temperature, dew point, and air mass frequency differed between high P&I mortality events (z$1) and non-events. To address the temporal autocorrelation in the weather variable time series and the resulting overestimate of the true degrees of freedom, the sample size was adjusted based upon the lag one temporal autocorrelation [42] (Wilks 2006) as follows: