Weather forecasts are just predictions and can never accurately tell you exactly what is going to happen. The closer they get to the weather event, the more accurate they become.
There are many different factors that can affect weather, including the sun, land formations, and the rotation of Earth. The energy that Earth receives from the sun is a major driving force in our weather. The heat from the sun warms the Earth's surface, creating differences in temperature that result in warm and cold air masses. The day/night cycle also plays a role in weather, with warmer temperatures during the day and cooler temperatures at night.
Land and water heat unevenly, with land heating faster than water. This uneven heating leads to differences in pressure, creating wind and atmospheric motion. Air moves from areas of high pressure to areas of low pressure, creating weather systems.
The rotation of Earth leads to differences in weather across different regions. Earth's revolution around the sun also contributes to seasonal weather changes.
Landforms like hills and mountains can affect weather as well. When wind hits a mountain, it is forced to rise, cool down, and release moisture, leading to precipitation on one side of the mountain. On the other side, the wind is weakened and has less moisture.
Overall, weather is a complex and dynamic system influenced by numerous factors that scientists gather and analyze through computer models in order to make predictions.