Although asserting God’s greatness based on gevurot geshamim – i.e. stating mashiv ha-rua’h u’morid ha-geshem (He who makes the winds blow and brings down the rain) in the blessing of mehayye ha-metim (He who revives the dead) – is an essential part of our Amida prayer, the baraita on our daf teaches that it is not essential to relate similarly to the falling of dew or the blowing of wind.
The Gemara asks: What is the reason that this recitation is optional? Rabbi Hanina said: Because winds and dew are consistent and not withheld, since the world could not exist without them, their mention is optional.
Dew is created by condensation of moisture in the air. Most objects – including plants – radiate (and lose) more heat than the air surrounding them, and thus become colder than the air. At that point atmospheric moisture condenses at a rate greater than that at which it can evaporate, forming water droplets. Although there are specific conditions that may limit the development of dew (e.g. low clouds, strong winds, etc.), since dew is created locally and is not connected with the larger water system, there is almost always some dew created.
The amount of dew that falls differs with climate and region; there are places in Israel where the amount of dew is almost equal to the amount of rainfall in a given year. In such places, it is only because of the dew that agriculture can be maintained.
Although an overabundance of dew can occasionally cause damage to produce at certain times of the year, generally speaking dew is seen as valuable – both in the summer when it acts as a water source, and in the winter when it protects the ground from frost.
Winds are created by a variety of different factors. Differences in temperature between the ground and the air, between the sea and the land, and between the Arctic Circle and the Equator all play a role in the creation of wind. Although the systems that create winds that carry rain are complicated, the agents involved in creating wind are constant; there is always some movement of air and never a total cessation of wind.
Rashi explains that the ruling of the baraita that one is not obligated to mention dew or winds refers to the winter. The Ritva, however, understands that it is a reference to the summer, when gevurot geshamim is not recited, and the ruling is that even in places where the custom is to mention these natural phenomena, it is not essential to do so. In fact, there are different traditions regarding this question. Sefardim and Hassidim do insert morid ha-tal in their Amida, while the traditional Ashkenazi position is to leave it out. In Israel the custom is for everyone to include it in their prayers (see Shulḥan Aruk Orah Hayyim 114:7).