# Portfolio risk estimation through variance covariance matrix

Is the portfolio risk calculated through variance covariance matrix an estimate of the current risk of the portfolio? Suppose I am using the weights as of today, and I have estimated the variance covariance matrix from historical returns of the assets and I calculate portfolio risk as wVw'. Is it an estimate of the future risk in the portfolio?

How does this estimate relate to the realized portfolio risk i.e. the standard deviation of the portfolio returns?