By Renny Vandewege
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(Source: YouTube)
Most weather forecasts include predictions for at least the next seven days, but how accurate are these long-range forecasts? Can we really trust them?
Yes and no. Predicting rainfall and exact temperatures seven days in advance is a daunting task. In general, seven-day forecasts tend to be pretty accurate for the first few days, but their accuracy often decreases during the last several days.
The truth is that even measuring the accuracy of a forecast is challenging. Rain forecasts are usually based on the probability of precipitation over a given area - such as a 40% chance of rain across a television-viewing area. Most official rainfall data is recorded from gauges at select locations, so if rain fell elsewhere in the region but not over those gauges, the data wouldn't accurately depict actual rainfall in the region. Still, in various detailed studies, researchers have concluded that forecast accuracy goes down the farther into the future meteorologists tried to predict.
The goal of a long-range forecast should really be to predict the trend in weather as opposed to exact details. This includes rain chances and temperature trends. Nevertheless, people want exact high and low temperatures in their forecasts, so meteorologists provide them. But in a meteorologist's perfect world, forecasts four to seven days in advance would include general trends. Instead of saying that the high on a given day would be 81, for example, a forecaster might say that highs would be in the upper 70s to low 80s.
Why is forecasting four to seven days out such a challenge? For most forecasts, meteorologists analyze computer models. A computer model uses current weather conditions and mathematical equations to predict weather. In short-term forecasts - those covering the next one to three days - forecasters use high-resolution models. These models do a good job of factoring in small details, such as the exact positioning of cold and warm fronts and local terrain that might influence weather. This results in fairly accurate forecasts for the first three days.
But once forecasters try to predict weather four to seven days off, they have fewer models to analyze, and the models they can look at don't take into account the same kinds of small, telling details. Forecasters must then employ a process known as "ensemble forecasting" that takes into account multiple models. When the models are consistent, meteorologists have more confidence in their forecasts.
Another technique used for long-range forecasting makes use of something called teleconnections. A teleconnection is a series of weather data recorded at two locations very far apart. For example, the most well-known teleconnection is the El Niño Southern Oscillation index, which looks at ocean temperatures at the equator in the Pacific Ocean. ENSO offers insight into global patterns that may influence weather.
Finally, meteorologists use climatological data to analyze how the atmosphere has performed historically in similar situations to get an idea of how an upcoming weather pattern may impact an area.
Though meteorologists are good at identifying temperature and precipitation trends a week away, the exact details of a seven-day forecast can be hard to pinpoint. But there is good news: As computer models improve, the accuracy of seven-day forecasts will likely improve, too.
RELATED ON SKYE: 50 Must-See Weather Photos from 2012
Image may be NSFW.
Clik here to view.
Image may be NSFW.
Clik here to view.
(Source: YouTube)
Most weather forecasts include predictions for at least the next seven days, but how accurate are these long-range forecasts? Can we really trust them?
Yes and no. Predicting rainfall and exact temperatures seven days in advance is a daunting task. In general, seven-day forecasts tend to be pretty accurate for the first few days, but their accuracy often decreases during the last several days.
The truth is that even measuring the accuracy of a forecast is challenging. Rain forecasts are usually based on the probability of precipitation over a given area - such as a 40% chance of rain across a television-viewing area. Most official rainfall data is recorded from gauges at select locations, so if rain fell elsewhere in the region but not over those gauges, the data wouldn't accurately depict actual rainfall in the region. Still, in various detailed studies, researchers have concluded that forecast accuracy goes down the farther into the future meteorologists tried to predict.
The goal of a long-range forecast should really be to predict the trend in weather as opposed to exact details. This includes rain chances and temperature trends. Nevertheless, people want exact high and low temperatures in their forecasts, so meteorologists provide them. But in a meteorologist's perfect world, forecasts four to seven days in advance would include general trends. Instead of saying that the high on a given day would be 81, for example, a forecaster might say that highs would be in the upper 70s to low 80s.
Why is forecasting four to seven days out such a challenge? For most forecasts, meteorologists analyze computer models. A computer model uses current weather conditions and mathematical equations to predict weather. In short-term forecasts - those covering the next one to three days - forecasters use high-resolution models. These models do a good job of factoring in small details, such as the exact positioning of cold and warm fronts and local terrain that might influence weather. This results in fairly accurate forecasts for the first three days.
But once forecasters try to predict weather four to seven days off, they have fewer models to analyze, and the models they can look at don't take into account the same kinds of small, telling details. Forecasters must then employ a process known as "ensemble forecasting" that takes into account multiple models. When the models are consistent, meteorologists have more confidence in their forecasts.
Another technique used for long-range forecasting makes use of something called teleconnections. A teleconnection is a series of weather data recorded at two locations very far apart. For example, the most well-known teleconnection is the El Niño Southern Oscillation index, which looks at ocean temperatures at the equator in the Pacific Ocean. ENSO offers insight into global patterns that may influence weather.
Finally, meteorologists use climatological data to analyze how the atmosphere has performed historically in similar situations to get an idea of how an upcoming weather pattern may impact an area.
Though meteorologists are good at identifying temperature and precipitation trends a week away, the exact details of a seven-day forecast can be hard to pinpoint. But there is good news: As computer models improve, the accuracy of seven-day forecasts will likely improve, too.
RELATED ON SKYE: 50 Must-See Weather Photos from 2012
Image may be NSFW.
Clik here to view.
