First Alert Weather In-Depth: How do we forecast at medium range?

How do we forecast for extended periods of time?

How do we forecast for extended periods of time?

Friday has been the day when Rochester’s Only 10 Day Forecast has started to show the forecast for the eclipse. First Alert Meteorologist Stacey Pensgen had the first look at the weather for April 8 starting Friday evening at 4 p.m. With that said, just how accurate are numerical weather models that far out — and how do meteorologists forecast for longer periods of time if weather models are not so accurate?

First off, lets go into how accurate models are in the medium range.

Numerical weather prediction has gotten a lot better since its implementation, but it isn’t 100% just yet. (This is why meteorologists have a job and will continue to have a job, as 100% accuracy is nearly impossible.) Let’s start off where numerical weather prediction stands for 10 days out and then work ourselves closer. As of today, numerical weather prediction 10 days out is less than 50% accurate as it stands near 42%. Although that does not look pretty, models get significantly better starting at seven days. A seven-day forecast on numerical weather prediction is roughly 72% accurate. Pretty good, but not what we would desire for a complete takeover. At five days out, numerical weather data is about 88% accurate; and at three days, its about 95%. As you would have realized, the closer we get to the day of forecast the computers get better. Even with that said it is not 100% accurate, which is where meteorologists come in. A major part of a meteorologist’s job is to understand these weather models, digest the data, and then accurately predict what is expected based off the data, however, at different days out the approach is different.

Meteorology in its essence is the study of chaos theory. The saying that a butterfly flapping its wings in Argentina can cause a tornado in the Great Plains is not entirely fact, but has some ground because the wind blowing in one direction on day 1 could have implications on what’s expected on day 3, and then that change on day 3 affects how days 7 and 8 play out. Basically chaos, because one change can send a chain reaction that could be felt for hours, days, and even months. This is where numerical weather prediction has come in to help us as meteorologists predict the weather, but as we just talked about it is not entirely accurate. Meteorologists come into play to analyze the data, and then base a forecast on what is given to them and on what they know from past similar events and schooling.

When we look at the 7-10-day range (where the eclipse forecast stands on March 29, 2024), it is all about Pattern Recognition. Pattern recognition is an essential skill as a meteorologist. Exacts at this range are very foggy and unclear, and pattern recognition allows us to dissect the overall weather pattern to determine if it is favorable for warm and rainy/clear or cold and snowy. Then we move into the 5-7-day timeframe. The 5-7-day timeframe is about increasing or decreasing confidence with trends. We talk about it all the time: “Oh, the trends this morning are or are not looking good for snow or warmth or whatever it is.” Monitoring trends is key because some models have biases and as the days get closer they trend one way or another. Also using the skill of pattern recognition we can see trends coming. Then we get closer and move into the 3-5-day forecast. At this point, we don’t iron out exacts just yet but the picture becomes much clearer.  In this timeframe we begin to see whether or not the precipitation type could be snow, ice, or rain; if it will be warm or cold; and in the eclipse’s case whether or not we will have sun or clouds. Finally we are inside three days. This is where we iron out all the details. This is when we begin to show snow maps, rain maps, expected wind gusts, exact timing, and even the amount of cloud cover at certain times in the day.

A lot goes into making a forecast, let alone a medium or long-range forecast. With that said, yes numerical weather prediction has made it easier, but it’s still far from perfect and so we as meteorologists will continue to have a job. So, with the eclipse forecast just be aware that it will continue to change leading up to the day of, so make sure you stay with the First Alert Weather Team as we get you prepared with what you need to know and if we will be able to capture the eclipse.