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:

15823.283396314564 gram * millibar / kilogram

Take the odd units and force them to millibars

print(e.to(units.mbar))

Out:

15.823283396314565 millibar

Take the raw vapor pressure and throw into the dewpoint function

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

Out:

13.854135353732214 degree_Celsius

Which can of course be converted to Fahrenheit

print(td.to('degF'))

Out:

56.9374436367179 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:

13.449790886867381 millibar

And print the corresponding dewpoint

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

Out:

11.376545231347285 degree_Celsius 52.47778141642504 degree_Fahrenheit