> if none required. Default <code>NA</code>.</p></dd>


<dt>roll_days</dt>
<dd><p>Numeric value of the number of days to apply a rolling mean. Default <code>1</code>.</p></dd>


<dt>roll_align</dt>
<dd><p>Character string identifying the direction of the rolling mean from the specified date, either by the first 
(<code>'left'</code>), last (<code>'right'</code>), or middle (<code>'center'</code>) day of the rolling n-day group of observations. 
Default <code>'right'</code>.</p></dd>


<dt>water_year_start</