Weather Magick is simply willing a change or influence in the patterns of the sky to suit your own benefit. Individual practice doesn't have a large sway over the weather, but you can likely influence it marginally. Naturally changing rain to sun in the span of a few minutes is not a possibility but since the debate is so large I tried to rationally explain everything best I could. Whether or not you ultimately believe the practice can be used is entirely up to you.
Weather magick, unlike most, is something that can have consequences when used too frequently. Ex: channeling energy towards a downpour when your land is already flooding. Similarly, it shouldnt go out of balance with the natural cycle of the seasons. Ex: Channeling energy for snow in the midst of a summer heat. You could inherently create more chaos by doing this instead of going with the flow, and you won't be successful in doing so.
This is not a Magick based on will alone, as one should be able to determine a few things in their practice. Examples of this are: timing, amount of a given rainfall, wind speed and frequency of gusts, in addition to which towns/cities will be most impacted by the weather system.
Successful weather Magick is also best achieved in a community of practitioners in comparison to an individual, since you can raise more energy towards a specific goal. There's a heavy debate in the pagan and witchcraft community on if a single practitioner of weather magick can be enough to give way to a change in weather. An example of people working towards a change in weather would be school children involuntarily putting energy towards a heavy snow day. This tends to worsen the weather more than any previously predicted change in forecast, but schools will do anything to keep their doors open, even if means freezing a bunch of adolescents.
Harnessing Weather Energy:
Knot Magick is the use of a cord or knot which acts as a channel for magick energy. To utilize this, get as close to a storm as you can, or alternatively, just open up a window. Imagine the knot/cord absorbing the energy from the storm through the distal end. Imagine and feel this energy travel into the center of the knot/cord and from there you could save it for later use or absorb it into your body as a means of harnessing it for magick purposes. However, this energy can also be absorbed through crystals and sigils should one wish to use it for such.
Forming a bond with the elements or a sky entity:
Take time to bond with the elements and get a feel for their presence. Notice how it feels when you take a breath of fresh air, when water gently brushes against your skin, when your bare feet touch the grass beneath you, and when you approach the warm flames of a crackling fire. All of these elements are interconnected and together they bring about balance in the universe. Always get a feel for the elements before you start tampering.
Gods and Goddesses of the sky are specialized in weather should you wish to ask for assistance in that domain. For a more specific change in weather, I've listed some examples below. Weather deities can offer you protection from a storm and work with you to safely influence the forecast should you consider leaving an offering.
Rain: Freyr, Porr
Snow: Khione, Ullr
Wind: Odin, Vayu, Enlil, Aeolus
Thunder/Lightning: Zeus, Thor, Leucetius, Taranis, Indra
Hail: Irpa, Porgeror
Stimulating objects or instruments in relation to your favored weather outcome can help channel energy towards it. Ex: banging a drum for thunder, a fan for a breeze, and so forth. It sets a steady rhythm and can put the mind into a deeper trance than normal visualization. You could also chant a phrase or sentence while doing this. A famous chant still used today, is "rain, rain, go away".
Dedicating time to visualizing and energizing a change in forecast, such as a newfound sun or breeze popping up, may also have an impact on weather. This is where knowledge of impact sites, wind speed, etc. are best utilized.
Sigils that symbolize a weather pattern could also be used for raising this energy or promoting a change, especially if they have been used to harness weather energy from a previous storm.
If you choose to divert a storm, know which direction you wish to direct it. If your area is slightly flooded and you wish to use your energy to direct a storm coming your way to the heavily flooded south, you'll be doing more harm than good. This is why awareness is always important, because what might suit your needs may only hinder the lives of the common good. If your town or city just so happens more flooded than the south, then directing a storm is inherently better than trying to dissipate it.
You could also attempt to diminish a storm, although it may not dissipate completely by the time it arrives. If anything, it has the potential to grow heavier in your area since you are shortening the time available for allotted rainfall. This is especially true if the storm has a very sudden onset, and in that case, ones best bet is to seek protection from the weather. This can be done by employing similar methods of visualization, chanting, energy raising, and sigil use from above. You could also invoke the aid of the elements or a specific sky deity as suggested.
In a basic gist you may use weather magick at your own risk, but don't expect yourself to somehow become a wielder of lightning. With that said, I hope you all have a blessed night.