So I have heard this saying a lot and would like to know if and why this is true because the leaves are upside down now and I have always been confused by this because some have told me nay and some yay.
This is the old saying, "When leaves show their undersides, be very sure rain betides." From the farmersalmanac.com:
The leaves of deciduous trees, like maples and poplars, do often to turn upward before heavy rain. The leaves are actually reacting to the sudden increase in humidity that usually precedes a storm. Leaves with soft stems can become limp in response to abrupt changes in humidity, allowing the wind to flip them over.
So, yes there seems to be some truth to this depending on the tree you are observing.
In addition, according to this boating site, the lower the leaves turn on the tree the more severe the storm will be, meaning that if only the tops of the tree is affected there's less chance of the rain fall being too severe. Jul 1, 2018 at 0:15
It's also an interesting evolutionary question. There may be a survival advantage in relatively humid areas for leaves that slip over and absorb more moisture. It happens (and is well documented), and a grad student in evolutionary biology who is looking for an interesting dissertation topic would do well to follow up on this. Jul 5, 2018 at 1:24