Instead of the unnecessary and sarcastic remark from the FO he could just as easily have given his reasoning to the Capt. as to why he had not already reacted to the approaching weather, CRM being a two way street.
Indeed. But in that case it is the duty of the FO to reinstate a cooperative environment by using CRM techniques to mitigate the Captain's unexplained and clearly unexpected actions; to understand why the Captain is making a certain decision especially if unexpected or seemingly unjustified. He doesn't have to be obsequious, cowering nor aggressive, defensive, but assertive, problem focused and professional...and respond appropriately (i.e. correct an error, accept the decision or suggest an alternative).