Global variables

Hi all,
I have integrated NodeRed with an iot system that constantly sends me the temperatures of a system.
I would like that nodered alert me by corro if the temperature passes a certain level.
So that it does not send false positives, the system should check that 3 consecutive readings are given below the threshold, for example.
How can I implement this in NodeRed? Can you declare variables that are kept between several executions of a flow in which to store the times the threshold has been passed?

yes - see context docs -