Why Weather Forecasts Are Never Certainties

Published: 29/07/2025

By Steve – Orcamet

One of the most common criticisms of weather forecasts is that they’re always changing. It might say dry on Monday, and by Tuesday you’re suddenly planning for rain. People get frustrated when they feel like the forecast keeps shifting or when it doesn’t match what they see out the window.

The problem is, a forecast is never a guarantee. It’s a set of probabilities based on what the atmosphere is doing now, and what it’s likely to do next. That likelihood can change as new information comes in, and that doesn’t mean the forecast was wrong, it means the system evolved and the tools adapted.

Forecasts are built on uncertainty

The atmosphere is constantly moving, and small changes in temperature, wind or moisture can lead to very different outcomes. Sometimes, just a slight difference in cloud cover during the morning can affect how unstable the air becomes in the afternoon. If that instability crosses a threshold, you might get showers. If it doesn’t, you might stay dry. The models don’t always catch that transition perfectly.

This is especially true for things like showers, thunderstorms, fog and sea breezes. These rely on local features, small temperature gradients and surface conditions that are difficult to resolve, especially if you’re using a low-resolution model.

Why forecasts change over time

Most forecasts update every six to twelve hours. Each time, they pull in new observations from satellites, weather stations, balloons and aircraft. If something has shifted slightly since the last update, the forecast will adjust. That might mean a band of rain arriving earlier, or a temperature dip being more severe than expected.

It’s not that forecasters are changing their mind. It’s that the atmosphere is dynamic, and the forecast reflects that.

Percentages are often misunderstood

A 30 percent chance of rain doesn’t mean it will rain for 30 percent of the day. It also doesn’t mean it will rain in 30 percent of the area. It means that, based on current data, there is a 30 percent chance that it will rain at that specific location during the given time window.

It’s a way of showing confidence. The lower the percentage, the more uncertain the outcome. The higher the percentage, the more likely the event. It’s not a measure of rainfall duration or intensity.

Confidence is more useful than certainty

Most clients don’t actually need a yes or no answer. They need a way of assessing risk. A good forecast will tell you not just what might happen, but how confident we are that it will.

That can change the way you make decisions. If you’re running an event and the confidence in rain is low, you might go ahead but have a plan in place. If the confidence is high, you might delay setup or change the schedule. The forecast doesn’t have to be perfect to be useful. It just has to give you enough warning to respond.

Making sense of a shifting picture

The key is not to treat the forecast as a finished product, but as a live process. If you understand what’s driving the changes, you can adjust more smoothly. That’s where having a meteorologist in the loop helps. They can interpret model changes, explain the reasons behind shifting confidence levels, and help you make a decision based on your own tolerances.

Whether you’re deciding to launch a boat, cancel a shift, move livestock, or rig a stage, it’s often the confidence, not the certainty, that gives you the best lead time.

Final thoughts

Forecasts are not promises. They’re tools to help you prepare and plan. If they change, it means something in the system changed, and that information is worth having. It doesn’t mean the forecast failed. It means it adapted.

No one can remove uncertainty completely. But with good information and proper interpretation, you can manage it. That’s what forecasting is for.