title: Monitor dask-xarray performance
body: <p>I have the following basic code which (I thought) should set up xarray to use a LocalCluster.</p>
  
  <pre><code>from dask.distributed import Client
  client = Client("tcp://127.0.0.1:46573") # this points to a LocalCluster
  
  import xarray as xr
  ds = xr.open_mfdataset('*.nc', combine='by_coords') # Uses dask to defer actually loading data
  </code></pre>
  
  <p>I now launch some task which also completes with no issues: </p>
  
  <pre><code>(ds.mean('time').mean('longitude')**10).compute()
  </code></pre>
  
  <ol>
  <li><p>I noticed that the tabs for the Task graph, Workers, or Task stream (among others) in the dask-labextension for my LocalCluster remain empty. Shouldn't there be some sort of progress displayed while the computation is running?</p></li>
  <li><p>Which leads me to wonder, how do I tell xarray to explicitly use this cluster? Or is <code>Client</code> a singleton such that xarray only ever has one instance to use anyway?</p></li>
  </ol>