Fix mdbz on cheyenne.

Xarray doesn't work with np.amax on cheyenne for some reason.

doc/source/new.rst

@@ -12,6 +12,8 @@ v1.1.1
   also included a patch for numpy.distutils.
 - Fixed a few unicode characters hiding in a docstring that were causing 
   problems on Cheyenne, and also building the docs with Sphinx with Python 2.x.
+- Fix issue with np.amax not working with xarray on Cheyenne, causing an error
+  with the mdbz product.
 
 
 v1.1.0

src/wrf/g_dbz.py

@@ -6,7 +6,7 @@ import numpy as np
 #from .extension import computedbz,computetk
 from .extension import _dbz, _tk
 from .constants import Constants
-from .util import extract_vars
+from .util import extract_vars, to_np
 from .metadecorators import copy_and_set_metadata
 
 
@@ -194,7 +194,7 @@ def get_max_dbz(wrfin, timeidx=0, method="cat",
         be a :class:`numpy.ndarray` object with no metadata.
     
     """
-    return np.amax(get_dbz(wrfin, timeidx, method, squeeze, cache, meta,
-                           _key, use_varint, use_liqskin), 
+    return np.amax(to_np(get_dbz(wrfin, timeidx, method, squeeze, cache, meta,
+                           _key, use_varint, use_liqskin)), 
                   axis=-3)