# Weather Forecast Procedures and Products

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• 0:01 Weather Forecasting
• 0:50 Numerical Weather Prediction
• 2:48 Medium-Range Forecasting
• 3:53 Long-Rage Forecasts
• 5:20 Lesson Summary

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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

There are many ways to forecast weather, depending on how far into the future you're looking. In this lesson we'll explore three major forecasting procedures and see how they're applied.

## Weather Forecasting

I do a lot of camping and, when camping, it's pretty useful to know what the weather is up to, so we have a very sophisticated device to help with this. It's called a weather rock. Basically, you tie a rock to a string and hang it from the branch of a tree. If the rock is wet, it's raining. If the rock is dry, it's sunny. If the rock is moving, it's windy. And if the rock is gone, it's time to leave. Now, the weather rock works well enough for us, but some people prefer to have slightly more advanced systems of weather forecasting, or predicting future atmospheric conditions. Let's take a look at some of these and see how people predict the weather when a weather rock isn't quite enough.

## Numerical Weather Prediction

Next to simply looking outside, the most common form of forecasting today is called Numerical Weather Prediction, or NWP for short. This is a computer model that simulates atmospheric motion. It's a bit more complex than a weather rock. Basically, data is put into the model and the computer imitates normal atmospheric behavior, indicating how the observed conditions should change over time. From there, you can predict how weather will change. Now, no single model is always correct, so many forecasters rely on ensemble modeling in which numerous NWP models are compared to give a range of likely atmospheric behaviors.

Let's look at this a little more closely. There are three main phases to NWP forecasting. First is the analysis phase in which real, observable atmospheric conditions are recorded and entered into the computer model. This is important because the model has to have a baseline, something to start with, and the more accurate this is, the more accurate the results are likely to be. That brings us to the prediction phase. At this point, the computer models likely atmospheric behavior. To us, this may just look like lines moving around a screen, but for a professional forecaster, these changes in air pressure, temperature, and other variables indicate where various weather patterns are likely to occur. Finally, there's the post-processing phase in which computer-based statistical models both check the NWP model for errors and translate the data into common meteorological events. Basically, post-processing is an attempt to remove both human errors and system errors and it makes the wavy lines into something that the average person can interpret as clouds, rain, lightning storms, etc.

## Medium-Range Forecasting

Now, even with all the computer technology we have today, NWP forecasting is only really accurate for the immediate future. Beyond that, the variables become too hard to predict and even the most advanced super computers can only estimate about 6 days of weather. So we have different methods used for medium-range forecasting, defined as 3-7 days in the future. Computer models designed for medium-range forecasting are less interested in providing every detail about the future and are often more focused on relating likely future conditions to normal expectations. So, look for forecasts like temperatures above average, less than average precipitation, etc. There are two main programs that are recognized for their accuracy in medium-range forecasting. The Global Forecast System, produced by the National Centers for Environmental Protection, and the Integrated Forecast System, a global model created by the European Centre for Medium-Range Weather Forecasts.

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