The only bus service that is at Girona Airport is the service from the Airport to the main bus station in Barcelona as far as I know but if you have a look at
this site you might be able to find more info.
You wanted to know about the weather for March listed below is the info for March 2006
Date Max Temp Min Temp Max Wind Max Rain
Wed-01-Mar-06 11.6 3.6 10.5 0.01
Thu-02-Mar-06 15.3 1.2 21.0 0.00
Fri-03-Mar-06 18.4 5.3 36.5 0.01
Sat-04-Mar-06 17.2 12.3 46.0 0.00
Sun-05-Mar-06 16.9 3.1 49.0 3.43
Mon-06-Mar-06 16.5 4.5 33.0 0.00
Tue-07-Mar-06 15.0 7.5 26.0 0.00
Wed-08-Mar-06 16.9 6.9 10.0 0.00
Thu-09-Mar-06 18.1 6.6 25.0 0.07
Fri-10-Mar-06 18.0 6.4 20.0 0.76
Sat-11-Mar-06 16.1 7.1 35.0 0.37
Sun-12-Mar-06 17.9 8.6 28.0 0.00
Mon-13-Mar-06 14.2 3.5 14.0 0.00
Tue-14-Mar-06 16.8 2.0 13.5 0.00
Wed-15-Mar-06 15.8 4.7 28.5 0.00
Thu-16-Mar-06 16.5 4.8 11.0 0.00
Fri-17-Mar-06 16.4 4.6 14.0 0.00
Sat-18-Mar-06 15.9 11.6 10.0 0.00
Sun-19-Mar-06 13.9 10.6 17.5 4.29
Mon-20-Mar-06 15.9 11.3 25.0 0.00
Tue-21-Mar-06 19.1 9.5 29.0 0.00
Wed-22-Mar-06 19.7 8.2 11.0 6.79
Thu-23-Mar-06 20.4 6.2 21.0 0.00
Fri-24-Mar-06 20.1 11.8 33.5 0.00
Sat-25-Mar-06 21.8 9.4 24.5 0.00
Sun-26-Mar-06 18.0 8.5 40.0 0.00
Mon-27-Mar-06 19.2 12.6 21.5 0.00
Tue-28-Mar-06 18.7 7.8 15.0 0.00
Wed-29-Mar-06 19.3 7.4 18.0 0.00
Thu-30-Mar-06 19.0 6.9 24.0 0.00
Fri-31-Mar-06 21.3 10.0 9.0 0.00
Total for month 539.90 224.50 720.00 15.73
Adv for month 17.42 7.24 23.23 0.51