Rav Menachem Perl, Director of the Tzomet Institute, has issued a psak that people working the meteorological services are allowed to measure the levels of rainfall on Shabbos.

After being asked what is allowed and in what way, Rabbi Perl went to the national forecast headquarters in Bet Dagan to see how the measuring of rainfall is accomplished. The people measuring the rainfall use some sort of device that catches the rain and directs it via a metal pipe into a bottle. They then pour the collected rain water, in the morning, into some sort of measuring container, record the numbers, and report it to the national headquarters.

Rabbi Perl decided that even though Chazal say it is prohibited to measure on Shabbos, lest it cause you to write the measurements down, or possibly as being similar to work done during the weekdays, filling the bottle to be measured after Shabbos was never prohibited. Because measuring rainfall is a public necessity, as the rain levels are used to determine climate issues and then extrapolated to agriculture and all sorts of other public needs in settlement, economics and whatnot, this is considered a public need and a necessity for dealing with mitzvos.

So, rabbi Perl concluded, the people measuring the rainfall can put their empty bottles out on Friday and replace it on Shabbos morning with another empty bottle. Tranfering the collected water to the measuring container should be done after the conclusion of Shabbos and only then report it to headquarters.
source: INN