Nine years of daily insolation observations taken at Blue Hill, Massachusetts, were correlated, by month, with observations of temperature, snow cover, winds, sunshine, sky cover, pressure and precipitation. During all months of the year, the highest correlations were found between insolation and sunshine duration. Sky cover, precipitation duration and temperature range were also highly correlated with insolation. The “best” linear combination of specifiers of insolation were sunshine duration, precipitation duration and station pressure. When sunshine observations were excluded, the best linear combination of specifiers consisted of sky cover, precipitation duration and daily temperature range. The duration and time of occurrence of precipitation emerged as a potential specifier of insolation that has not been fully exploited.