pr=1013-.1055*elevation, where elevation is in meters

windk=24*windspeed*(2/3.74)^.2, where windspeed is in meters per second

tempav=(max temp+min temp)/2, where temperatures are in degrees C

apa=7.5*max temp/(max temp+237.3)

svpma=6.108*10^apa

avpma=svpma*max humidity/100, where humidity is in %

api=7.5*min temp/(min temp+237.3)

svpmi=6.108*10^api

avpmi=svpmi*min humidity/100

vpsl=(svpma+svpmi)/2

vpal=(avpma+avpmi)/2

hl=595-.51*tempav

rn=.95*(1-.21)*solar radiation-64, where solar radiation is the daily accumulated solar radiation in Langleys

delta=33.8639*(.05904*(.00739*tempav+.8072)^7-.0000342)

gamma=.242*pr/(.622*hl)

ea=15.36*(1+.0062*windk)*(vpsl-vpal)

An Excel spreadsheet comparing the method used by the NMCC to the Penman-Monteith equations is available here.