The image above shows the humidity forecast for Wednesday night in the SE US. It was generated on NCAR’s WRF weather model, using GFS forecast boundary conditions. Note that southeast of the frontal boundary, H2O concentration in the atmosphere is very high – between 15,000 and 20,000 ppm (compared to 390 ppm of CO2.) Northwest of the frontal boundary H2O concentration is much lower – between 3,000 and 6,000 ppm, which is still 10-20X higher than the amount of CO2.
The convergence of cold dry air and warm moist air will produce violent weather along the frontal boundary.
H2O is a much more potent greenhouse gas than CO2 and it is also much more abundant and much more variable than CO2. The graph below plots the four day forecast change in humidity in NW Georgia starting early this morning. CO2 is plotted in pink across the bottom.
H2O concentrations can change by 15,000 ppm in a matter of minutes – but of course that isn’t important. What is important is 100ppm of CO2 changing over a century.