As a deep cyclone moved into the Chukchi Sea on Friday, CPC's Arctic Oscillation index exceeded 3.

Only 14 prior October days have seen the AO exceed 3 since 1950, and none since a three-day stretch in 2008. pic.twitter.com/MpGkwkfaC9

— Dr Simon Lee (@SimonLeeWx) October 9, 2022