title: Metpy mpcalc.absolute_vorticity() with incompatible grids
body: <p>I'm attempting to follow <a href="https://unidata.github.io/python-training/workshop/MetPy_Advanced/qg-analysis/" rel="nofollow noreferrer">this training example</a> to calculate QG omega on NCEP/NCAR data but I'm getting hung up on mpcalc.absolute_vorticity.</p>
  <pre><code>import xarray as xr
  import metpy.calc as mc
  import metpy.constants as mpconstants
  from metpy.units import units
  import numpy as np
  
  path='./'
  uf = 'uwnd.2018.nc'
  vf = 'vwnd.2018.nc'
  af = 'air.2018.nc'
  
  ads = xr.open_dataset(path+af).metpy.parse_cf()
  uds = xr.open_dataset(path+uf).metpy.parse_cf()
  vds = xr.open_dataset(path+vf).metpy.parse_cf()
  
  a700 = ads['air'].metpy.sel(
          level=700 * units.hPa,
          time='2018-01-04T12')
  u700 = uds['uwnd'].metpy.sel(
          level=700 * units.hPa,
          time='2018-01-04T12')
  v700 = vds['vwnd'].metpy.sel(
          level=700 * units.hPa,
          time='2018-01-04T12')
  
  lats = ads['lat'].metpy.unit_array
  lons = ads['lon'].metpy.unit_array
  X, Y = np.meshgrid(lons,lats)
  dx, dy = mc.lat_lon_grid_deltas(lons,lats)
  
  avort = mc.absolute_vorticity(u700,v700,dx,dy,lats)
  </code></pre>
  <p>I get the error, &quot;ValueError: operands could not be broadcast together with shapes (73,144) (73,) &quot;.</p>
  <p>Full error traceback below:</p>
  <pre><code>Traceback (most recent call last):
    File &quot;metpy.decomp.py&quot;, line 43, in &lt;module&gt;
      avort = mc.absolute_vorticity(u700,v700,dx,dy,lats) 
    File &quot;/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/xarray.py&quot;, line 570, in wrapper
      return func(*args, **kwargs)
    File &quot;/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/units.py&quot;, line 312, in wrapper
      return func(*args, **kwargs)
    File &quot;/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/calc/kinematics.py&quot;, line 639, in absolute_vorticity
      return relative_vorticity + f
    File &quot;/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/pint/quantity.py&quot;, line 754, in __add__
      return self._add_sub(other, operator.add)
    File &quot;/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/pint/quantity.py&quot;, line 75, in wrapped
      result = f(self, *args, **kwargs)
    File &quot;/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/pint/quantity.py&quot;, line 686, in _add_sub
      magnitude = op(self._magnitude, other._magnitude)
  ValueError: operands could not be broadcast together with shapes (73,144) (73,) 
  </code></pre>