Clear skies continue over southern Ontario this week as a result of a persistent block pattern, with a ridge blocked over Ontario. The upper level ridge and a surface high pressure ridge over Ontario are resulting in clear skies and the nearly stationary pattern is resulting in little change from day to day and night to night. Other features of the block pattern that strengthen the block include deep troughs over the Atlantic and Pacific coasts and a ridge over the north Atlantic. The chart below shows the 250 hPa winds clearly tracing the ridge over Ontario and trough on each side of the ridge (as well as a weak trough south of the Great Lakes).