title: Check if there are 3 consecutive values in an array which are above some threshold
body: <p>Say I have a np.array like this:</p>
  
  <pre><code>a = [1, 3, 4, 5, 60, 43, 53, 4, 46, 54, 56, 78]
  </code></pre>
  
  <p>Is there a quick method to get the indices of all locations where 3 consecutive numbers are all above some threshold? That is, for some threshold <code>th</code>, get all <code>x</code> where this holds:</p>
  
  <pre><code>a[x]&gt;th and a[x+1]&gt;th and a[x+2]&gt;th
  </code></pre>
  
  <p>Example: for threshold 40 and the list given above, x should be <code>[4,8,9]</code>.</p>
  
  <p>Many thanks.</p>