During winter months, we say "You make the wind blow and the rain fall". During the summer, we say only "You make the dew fall." Why don't we include the beginning part about blowing the wind? I noticed that during Tefillat Tal on the 1st day of Pesach, we say the full phrase Mashiv Haru'ach umorid hatal. Why is that the only exception?
The Aruch Hashulchan OC 114:1 writes that "generally speaking wind brings clouds from which rain falls and therefore we mention them together". Being that wind is not directly associated with the gathering of dew it is not mentioned together. However, Shulchan Aruch OC 114 does state that if one mentions "mashiv haruach" in the summer he does not have to repeat the prayer.
The mention of ruach in Teffilas Tal seems to be in order to fill the meter of the poem.
There is a scientific answer, actually:
a windy night will often end up free of dew, because the resulting mixing of the lower atmosphere prevents the surfaces from cooling sufficiently by constantly transporting a fresh supply of warmer air to the surface from a few hundred feet up.
Fog is an "enhanced" form of dew. One can easily simulate the experiment by taking a hot shower such that it fogs up the bathroom. If you turn on a fan, the fog almost immediately dissipates.
Thus, generally, wind and dew are incompatible.
Because dew doesn't require wind, whereas rainstorms, especially in Israel, do. (Dew forms from condensation, but rain requires clouds which need to get blown by the wind.)
I don't know why there is an exception for the first time. Maybe as a transition.
No sources, sorry.