Skew-T Procedure

From the temperature (T) curve at the given pressure on the sounding, always follow the isotherm to the 622 hPa isobar. The value of the saturation mixing-ratio line, read by interpolation if necessary, through this point at 622 hPa gives the saturation vapor pressure in hectopascals (hPa) at the given pressure. In this example, air at a pressure of 850 hPa with a temperature of 3°C has a saturation vapor pressure of 7.5 hPa.

Note that the procedure to find the vapor pressure is quite similar to the procedure to find the saturation vapor pressure. The only difference is that one starts with the dewpoint to find the vapor pressure, while one starts with the temperature to find the saturation vapor pressure.

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