Triple digit temperatures were noted over many Northeast locations during the 3 day period 3-5 July 1966.

Below are 500 and 850 hPa charts for this record breaking heat event over the Northeast. Notice how there was not an imposing upper level ridge but significant deviation above climatology of the 850 hPa thermal field. The high 850 temperatures coupled with downsloping were likely the key contributors of the heat wave.