How do weather patterns evolve? What can cause this?

The global weather pattern evolves with evolving pressure systems and jet stream on the planet. Winds blow from high-pressure systems to low-pressure systems. When these prevailing winds travel over oceans, then they cause rain inland. If the winds are dry they cause drought over an area.

The weather patterns and mainly driven by two factors; The sun position relative to the earth ad the tilt of the planet to the plane of its orbit. This causes uneven heating of the earth surface hence some areas warm up faster than others. This also changes with the position of the earth, in its orbit, relative to the sun hence casing seasons. Areas that warm faster due to the position of the sun, relative to latitude, become low-pressure systems while those with the cooler atmosphere are high-pressure systems. These systems are dynamic.