• Cory Smith

Why your 7-day forecast is REALLY good




As meteorologists, we love to brag about how "Accurate" our forecast is on-air but how close are we actually, and are there inherent issues with your 7-day forecast? When it comes down to it, your 7-day forecast, in general, is really good. But how good is it? Well, for this article we will be using data from an excel sheet I use to track how good my forecasts are. While the data shows results that are specific to me forecasting Lafayette the overall trends are applicable for forecasts in general.


Let's start with something you probably already know. Your next day forecast is more accurate than your 7th day forecast. The reason for this is pretty simple. We use current conditions, our own weather knowledge, and models to forecast the weather. Outside of the first 2 days the current conditions likely have little bearing on the forecast. As for the models, they are huge supercomputers trying to guess the weather. Of course, decades of scientific research has gone into these models but in the end, they aren't perfect. This translates to the models being less and less accurate the further you look out and makes it harder for us to forecast with precision in these later days.

These 3 things result in a forecast with error that looks something like this:





So let's break down what you are seeing.

  1. Your day 1 forecast is the "best"

  2. Your day 7 forecast is the "worst"

  3. Overall an average forecast is only off by a maximum of 3.22° for your high and 4.46° for your low which is pretty darn good!

Overall, what this all means is your 7-day forecast is really good! As far as the high temperature is concerned, most days are likely to be within 3 degrees of the actual temperature. For most, you wouldn't even notice the difference between the few degrees. As for rainfall forecasts, that is something much more difficult to forecast and maybe another topic for another day!



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