Dewpoint and Mixing Ratio

Use functions from metpy.calc as well as pint’s unit support to perform calculations.

The code below converts the mixing ratio value into a value for vapor pressure assuming both 1000mb and 850mb ambient air pressure values. It also demonstrates converting the resulting dewpoint temperature to degrees Fahrenheit.

import metpy.calc as mpcalc
from metpy.units import units

Create a test value of mixing ratio in grams per kilogram

mixing = 10 * units('g/kg')
print(mixing)

Out:

10.0 gram / kilogram

Now throw that value with units into the function to calculate the corresponding vapor pressure, given a surface pressure of 1000 mb

e = mpcalc.vapor_pressure(1000. * units.mbar, mixing)
print(e)

Out:

15823.863685716977 gram * millibar / kilogram

Take the odd units and force them to millibars

print(e.to(units.mbar))

Out:

15.823863685716978 millibar

Take the raw vapor pressure and throw into the dewpoint function

td = mpcalc.dewpoint(e)
print(td)

Out:

13.854699858753728 degree_Celsius

Which can of course be converted to Fahrenheit

print(td.to('degF'))

Out:

56.93845974575668 degree_Fahrenheit

Now do the same thing for 850 mb, approximately the pressure of Denver

e = mpcalc.vapor_pressure(850. * units.mbar, mixing)
print(e.to(units.mbar))

Out:

13.45028413285943 millibar

And print the corresponding dewpoint

td = mpcalc.dewpoint(e)
print(td, td.to('degF'))

Out:

11.377098919513376 degree_Celsius 52.47877805512405 degree_Fahrenheit

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