That's pretty location dependent though. Here locally we've had a number of colder or longer-lasting inversions in the last quarter century. December 2011 for example never even gets brought up and it produced sub-freezing highs here.

Come on dude... Maximum 3-Month Mean Avg Temperature for SALEM AP (MCNARY FIELD), OR Rank, Value, EndingDate, MissingDays 1, 70.9, 2022-09-30, 0 2, 70.9, 2024-09-30, 0 3, 70.6, 2021-09-30, 0 4, 70.5, 2014-09-30, 0 5, 69.8, 2017-09-30, 0 6, 69.4, 2023-09-30, 0 7, 69.2, 2015-09-30, 0 8, 68.5, 2013-09-30, 0 9, 68.4, 2018-09-30, 0 10, 68.3, 1900-09-30, 30 Period of record: 1893-01-01 to 2025-01-06

Too Cold to Snow!

OLM has fallen from grace, we all know that. If you want to cherry pick, EUG put up 9 days in the 30s. Outside of Jan 2013, you'd be hard-pressed to find an inversion the past 25 years that tops that.

Marry 1954, F Spring 2022, Kill this winter.