GRIB2: TypeOfLevel 17 and 18 should be mapped to levtype 'sfc'
14 14 Level of free convection (LFC) (-)
15 15 Convective condensation level (CCL) (-)
16 16 Level of neutral buoyancy or equilibrium level (LNB) (-)
-17 17 Departure level of the most unstable parcel of air (MUDL)
-18 18 Departure level of a mixed layer parcel of air with specified layer depth (Pa)
+17 sfc Departure level of the most unstable parcel of air (MUDL)
+18 sfc Departure level of a mixed layer parcel of air with specified layer depth (Pa)
# 19 Reserved
20 20 Isothermal level (K)
21 21 Lowest level where mass density exceeds the specified value (base for a given threshold of mass density) (kg m-3)
