What is a weather model? How is a forecast generated? Why should I care? These are all valid questions.
Weather models are the basis for weather forecasts. They can give meteorologists a better understanding of the future state of the atmosphere, and indicate which areas will be affected by adverse weather. A good forecast requires good observational data that includes temperature, dew point, atmospheric pressure, and wind speed. This data is collected at airports, National Weather Service offices, and by weather balloons. Meteorologists rely on the accuracy of this data to make a sound forecast.
The issue is that this data is collected in sporadic locations throughout the continental United States. Computer models require observations to be input in a gridded format. Unfortunately, cities across the U.S. are not situated in a grid. To fix this issue, every observation is ingested into a computer model. The model then carries out intricate number-crunching that puts those numbers onto a grid horizontally (from point A to point B) and vertically (from the ground to above the clouds). Computers make these calculations in a matter of minutes, a process called data assimilation.
All weather models are not created equally
Weather models can vary widely: by forecast length, model runs per day, resolution (how many kilometers between horizontal grid points), and forecast location. The output from each model is different. This is where a meteorologist steps in. A meteorologist will look at the output from various models and model run times to see which output is the best fit for an accurate forecast. They may make adjustments to their forecast based on the current state of the atmosphere. Then a meteorologist provides their forecast to the consumer.
You, as a consumer of weather information, care about the forecast. Weather affects your daily life. It helps you decide what to wear and how to focus your daily activities. Weather models help meteorologists tell you how your day and week will evolve, and they help you plan for what is to come. You should keep checking the forecast for updates during the week because your life, as well as the atmosphere, is constantly evolving. Meteorologists (and weather models) work around the clock to bring you their best forecast for the future state of your week.
Thank you to everyone who attended our talk, “How is a Weather Forecast Generated and Why is that Important to Me?” at APWA 2019 in Salt Lake City. The session created a lot of discussion and we really enjoyed meeting you all.
About the Author:
Brianna Kump is a road weather meteorologist at Iteris.