How to create a loop that checks if a value is greater than AND stays greater than some number for a certain # of days?

First and foremost, thank you for taking your time to view my question.

My question is regarding a flag that I am trying to create: Essentially the flag works like this: - If the value of column vals is greater than 3 for 3 consecutive days, I want the original value to be flagged. I am trying to use an ifelse statement, however, I just don't know how to code the "stays greater than 3 for 3 consecutive days" in R. I have tried for multiple hours without no solution :/

The sample data might looks something like this

Date      Vals
8/1/11     2.5
8/2/11     2.6
8/3/11     1.6
8/4/11     3.6
8/5/11     3.5
8/6/11     3.1
8/7/11     3.8
8/8/11     2.1
8/9/11     1.6
8/10/11    3.1

So essentially: I would get a third column called FLAG that would only list error on 8/4/11 and 8/5/11 column and NO ERROR on the rest.

Please let me know, and thank you for your time!