MetPy 1.0 Upgrade Guide

The 1.0 release marks the first release of MetPy to have what we call a “stable” interface. This means that code that works with a given release of MetPy 1 should work with all later versions of MetPy 1. Given those constraints, many of MetPy’s functions changed in some way in MetPy 1.0. In the majority of these cases, the change was to rename some of the function parameters for consistency (which only affects users passing in these parameters as keyword arguments). For more details see the full list of MetPy 1.0 API Changes.

The biggest change in MetPy 1.0 is expanded support for xarray DataArray instances as input to MetPy calculation functions. MetPy calculations can now return a DataArray when given such as input, and can also take advantage of the metadata available on a DataArray (such as coordinate information) in order to simplify code. For example, calculating the geostrophic wind used to look like:

# Read data and get the geopotential heights for a single time and level
ds = xr.open_dataset(get_test_data('irma_gfs_example.nc', as_file_obj=False))
height = ds.metpy.parse_cf('Geopotential_height_isobaric').isel(time1=0, isobaric3=0)

# All the calculations needed for geostrophic wind
dx, dy = mpcalc.lat_lon_grid_deltas(height.longitude.metpy.unit_array,
                                    height.latitude.metpy.unit_array)
f = mpcalc.coriolis_parameter(height.latitude.metpy.unit_array)
ug, vg = mpcalc.geostrophic_wind(height.metpy.unit_array, f[:, None], dx, dy)

These last three lines (of calculation) now become:

ug, vg = mpcalc.geostrophic_wind(height)

For more information on how to best use xarray, see the xarray with MetPy Tutorial.

In 1.0, we have also expanded our declarative plotting interface with more capabilities. For more information, see the MetPy Declarative Syntax Tutorial.