Students will be able to describe major concepts of how meteorologists predict the weather.
This tutorial includes essential question, videos from AccuWeather, notes adapted from the United States Search and Rescue Task Force (USSARTF) website.
How do meteorologists at AccuWeather make your forecast? Here's the four-step breakdown:
Getting in Touch with the Weather
The first step in making a forecast is to, as the meteorologists call it, "get in touch with the weather." That's when forecasters, as they start their shift, take a look at what weather happened in the past day. They also take a look at what weather is happening currently.
"If you don't know what happened yesterday and why, then the chances of you being able to forecast the future are less," AccuWeather Meteorologist Bernie Rayno said.
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Meteorologists look at observations around the Western Hemisphere, like temperature, pressure, wind speed and precipitation. They start by looking at patterns, which show the major characteristics of the atmosphere.
Like peeling an onion from the outside in, the forecasters start with the biggest movements in the atmosphere before looking at the smaller details. To analyze the weather, they use tools like satellite and radar.
One tool that mets use that doesn't get much attention is the surface map. Surface maps give meteorologists an idea into why weather is happening. When analyzing a surface map, meteorologists can see where some of the key players in the weather are located, like high pressure, low pressure, cold fronts, warm fronts, cloud cover, wind and precipitation.
"Storm systems move. They're like cars. So if you know what [weather conditions are] associated with the storm or this car, as it moves east tomorrow, you can kind of guess, 'Well, if this storm system is doing this here, it may be doing this in the location where I think it's going to be tomorrow.'"
When looking at a surface map, meteorologists can generally locate storm systems by looking for areas of low pressure. High pressure generally indicates fair weather.
Using the Models
The second step that forecasters use to make a forecast is looking at computer models. Forecasting models show some different scenarios of what could happen with the weather. In the United States alone, over 210 million observations per day (primarily from satellites) are recorded into the computer models that forecasters use.
"Meteorologists have computer models which model the atmosphere using parameters such as barometric pressure, temperature, humidity and a plethora more of complicated mathematical equations," AccuWeather Meteorologist Erik Pindrock wrote, in an article about Exponential Changes in Forecasting Technology.
Scientists constantly update the physics of the models so a weakness of a model today might not be tomorrow.
"Here in the 21st century," Pindrock wrote, "meteorologists have several dozen computer models to look at. Within some of these individual computer models are other model forecasts with a slightly different output. These other model forecasts are referred to as a model ensemble. In other words, you start out with a single model and you perturb or alter the initial atmospheric conditions of that model. The end result is five, 10 or maybe 20 or more different outputs of one particular computer model. So in reality, meteorologists have hundreds of computer weather models to choose from!"
The third step of making a good forecast is collaboration. Here at AccuWeather, a group of meteorologists meets at least three times a day to make decisions about difficult forecasts. Collaboration irons out extreme forecasts with compromise.
For example, one meteorologist might see a 3- to 6-inch snowfall from a storm that another meteorologist sees as leaving just a coating. When they compromise on their forecast, they're more likely to hit on what will actually happen.
A map discussion meeting at AccuWeather headquarters in State College, Pa.
"As in any field," AccuWeather Chief Meteorologist Elliot Abrams said, "where there may be differing opinions about things, and people have different levels of expertise, sharing and the give-and-take of ideas often lead to better product. Specifically, one person may be looking at a certain area and assessing one aspect of a weather forecast while a colleague may be looking at a different area. Working together they may think of things they hadn't thought of before for the forecast that they're working on."
The Sixth Sense
Lastly, some meteorologists say, tongue in cheek, that forecasting takes a sixth sense.
"I'm not saying that I can look into a crystal ball and say 'Aha! This is what's going to happen!' but the sixth sense [of forecasting] is used in conjunction with everything else: understanding the past, understanding the present," AccuWeather senior meteorologist Bernie Rayno said.
A forecaster's "sixth sense" develops over time. The "sixth sense" that meteorologists use is pattern recognition that comes from years of experience with forecasting. Weather cycles repeat, and when experienced meteorologists have seen certain cycles before, they use their gut feeling to guide their forecast.
Meteorologists are scientists who monitor weather conditions. They sample a wide network of weather stations and use satellite images to map out the positions of the large air masses circling the Earth. Since air masses interact in a relatively predictable way, meteorologists are able to predict weather patterns with some degree of accuracy.
Fronts are responsible for most changes in weather. They occur when a large mass of cold air meets a large mass of warm air. The front is the zone along which the masses come into contact with each other. Cold Fronts occur when a cold air mass, which has a high density, pushes under a warm air mass. The warm air is pushed upward at a sharp angle, causing moisture to condense rapidly. Heavy precipitation is often the result. Warm Fronts occur when a mass of warm air passes over a mass of cold air at a moderate angle.
Geography - While fronts indicate the character of prevailing weather systems, local weather is greatly influenced by geography.
Every weather prediction is based on the chance that the weather conditions will act together in a certain way. However, forecasts can be wrong. Some general patterns help meteorologists predict weather for a local area.
Most weather conditions across the United States move from west to east. Moving weather conditions are due to wind patterns across the earth. In any given place, a clue to tomorrow's weather may be found by looking at the weather of the area to the west.
However, geographic features in your area such as large bodies of water and mountains can affect local weather. For example, if you live near the Atlantic Ocean, conditions to the east often influence your weather. And whether you live near the east coast or west coast, temperatures near the ocean may be higher than they are even short distances inland. The heat-holding ability of large bodies of water causes warming of the air along the coast. In a city such as Chicago, which is located on Lake Michigan, forecasters often give two sets of information: one for people living within 5-10 miles of the lake, and the second for people in outlying areas. In the spring, for example, it's generally warmer in the outlying areas than it is closer to the lake.
People who live on the eastern side of a mountain range such as the Sierra Nevadas have mostly dry weather. Even when moisture-laden air masses move into the area, their interaction with the mountains causes most of the moisture to fall on the western slopes.
So keep in mind that you can't just look at a weather map and expect to make totally accurate predictions. Lots of factors affect what happens in an area on any given day.
For geography, remember these five points:
A brief look at how meteorologists (and regular folks) predict the weather