Jesus points out they can read basic signs in the skies to predict weather but refuse to recognise obvious signs such as the many miracles He has already accomplished. He declares He will not give them any sign but that of Jonah (Jonah 1:17), who was swallowed by the whale and restored on the third day (Matthew 16:1–4).
Now you know!
So, the colour of the sky has harboured a great number of folklore and sayings, and these are often correct, and scientifically proven. For example:
Similarly, ‘Rain Before Seven, Fine by Eleven’ is often correct because when there is rain, there are also strong winds and this usually means that early morning rain, will be blown away by midday.
Plants and wildlife can be observed to react to weather conditions too, for example:
There are plenty of sayings or proverbs pertaining to plants as well, such as
Onion-skins very thin
Mild winter coming in;
Onion-skins thick and tough,
Coming winter cold and rough.
When dew is on the grass, rain will never come to pass: Dew forms when grass gets colder than the dew-point temperature (the temp at which dew forms). At night, grass cools when heat from the ground radiates upward. In a clear, dry atmosphere, this heat escapes the atmosphere and rises into outer space. In a moist and humid atmosphere, water vapour absorbs some of that heat and can redirect it back down to the ground, warming up the grass, and thus keeping it dew free. Dew on the grass is therefore a sign of a high-pressure system, and good weather.
April showers bring May flowers:
Cool, wet weather in spring helps grass prepare for strong growth later in May.
The ash before the oak, choke, choke, choke.
The oak before the ash, splash, splash, splash:
This refers to which tree breaks bud first in the spring; If ash trees break bud before oak trees, this foretells a wet summer.
Pinecones open up when good weather is coming:
Scientifically based – as during dry weather, pinecones dry out, which causes their scales to stand out and appear more "open", whereas in wet weather, the scales curl up and the cones return to a more closed shape.
So - now you know [even more!].