The chachamim spread out through Eretz Yisrael to tell them to pray when they saw grains that were destroyed by wind even though it was only the size of the mouth of an oven.

Another case was when wolves ate two children beyond the Jordan river. R’ Yosee says not that the wolves ate the children but that they even looked at the children was a bad sign.

Taanis 3:7

On these things you even fast on Shabbos; on a city that is surrounded by non-Jews, a river is threatening to flood a city, a boat that imperiled in a storm. R’ Yosee says you can use the shofar to summon people to come to help in an emergency but not for prayer and crying out. Shimon Hateimani says even on pestilence we can call out for teshuva on Shabbos and the chachamim did not agree.