Add tests for shading areas on skewT diagrams
Add tests for shading areas on skewT diagrams

ahaberlie/MetPy,ShawnMurd/MetPy,jrleeman/MetPy,ahaberlie/MetPy,Unidata/MetPy,jrleeman/MetPy,Unidata/MetPy,dopplershift/MetPy,dopplershift/MetPy