March really is a great month to learn about weather. In the past week we've had snow, sleet, rain, sunny days, 60 degree weather... just about the whole range! Last year we did a more extensive unit on clouds- I brought that out again. But this year the interest seems to lie more in the water cycle.
You can find some free Water Cycle pages at Montessori Materials. They also have some awesome Cloud Nomenclature that we used last year.
NCAR (National Center for Atmospheric Research) has some awesome stuff for kids: http://eo.ucar.edu/webweather/ They have games, teachers info, ideas for experiments... check it out!
Montessori Printshop has free weather tracking cards to print out. I know we should use this more regularly... but we don't do it everyday.
We also did a fun experiment to observe water evaporation. We used:
Dropper to Transfer
Way to record (we used a dry erase board)
Transfer your water from a container into the rain gauge. Record how much water there is to begin with. Check back every day to see how much water evaporated.
And of course... you can use your weather station to actually measure the rain. That just requires some rain :)