The 1970 meeting was called of due to fog rather than snow. According to the Motoring News report it was abandoned at 1pm then the fog cleared within 30 minutes.
This was 1969, not 1970, I believe. The item in Autosport
for 31-Dec-70 is reproduced below. I don’t have a 1969 race [cancellation] report, but do have Autosport
for the following week (8-Jan-70) where an angry entrant took to the correspondence column to complain about the last-minute cancellation due to fog, arguing that it had been much worse during the practice sessions.
(Very OT, sorry, but that same 8-Jan-70 correspondence column features a letter from TNF’s Rob29 pointing out that Autosport
had got their Brazilian motor sport history wrong. Good to know that the TNF spirit was flourishing back in 1970. )