Meteorologists on the long-range forecasting team forecast trends in the weather over the next several months. Our mets and writers get a lot of questions about how long-range forecasting even possible. AccuWeather.com meteorologist Jack Boston answers some of the most-asked questions.
How detailed can you get with your forecasts so far ahead of time?
In long-range forecasting, we don't actually predict what's it going to be like every day. In other words, I can't sit here and say, "Well, on October 10th, it's going to be 60 degrees and party cloudy with showers in the afternoon." We don't do that. What we do is we look at a trend. "Overall, the month of October's going to be dry. Over all, the month of October's going to be colder than normal." Temperature forecasting might be a little bit easier than forecasting rainfall or snowfall
How far out do you forecast?
We have most of our confidence in the season that's coming up. We issue that forecast somewhere around two months ahead of time. There are some clients that are actually interested in next year, in next spring, in next summer. In fact, we actually look out a year and sometimes more than a year.
What factors do you look at when you're forecasting for a whole season?
We look at a number of things, but three majors factors we use in our season forecasts are ENSO, NAO, and analog years.
ENSO, or the El Niño-Southern Oscillation, is the La Niña and El Niño. What it basically is, when you take a long-term average, is if the sea surface temperatures in the Equatorial Pacific Ocean are above normal or below normal. If those temperatures are above normal, warmer than normal, we call that an El Niño. If those temperatures are below normal, we call it a La Niña. And that has a great affect on the type of weather in North America.
The NAO, or the North Atlantic Oscillation, is a relationship in temperature between the far-north Atlantic as compared to the temperature down near the Azores, off the coast of Spain. If it is warmer than normal up around Greenland, and colder than normal down around the Azores, that is what we call the negative NAO. That is what tends to cause blocking. If there is blocking in the Atlantic Ocean, weather systems coming across North America get forced down into the eastern United States, instead of just heading out into the North Atlantic. If that happens, that's how we get lots of cold air masses to come straight down into the Eastern United States, from Canada.
Analog years are past years that we see that have had similar precipitation and temperature patterns. We put them into our thinking as far what might happen this year might be similar to what happened in those years.
With so much uncertainty, why make a long-range forecast?
All I can say is that a [long-range forecasting] gives you an opportunity to plan. If it's going to be a snowy and cold winter, maybe you want to make sure your boots are in good shape. It's also very important to the energy industry because they have an opportunity to find out how much heating oil is going to be needed during the winter. They can plan that and buy a certain amount and make sure they keep a certain amount in supply.
The late-season swelter will continue along much of the Atlantic Seaboard through the week as tens of millions head back to school and work.
Tropical depression five has formed in the southwestern Gulf of Mexico's Bay of Campeche and will continue its west-northwest path during the next couple of days.
A second volcanic eruption occurred on Sunday morning in Iceland in the same area that had one on Friday.
Severe thunderstorms will threaten holiday festivities across parts of the Midwest and central Plains to close out the extended Labor Day weekend.
While flooding is a threat, monsoonal rains will be beneficial for most areas across northwest India this week.
Gusty winds, large hail and power outages occurred Sunday into Monday morning in the north-central United States.
Los Angeles, CA (1955)
110 degrees, hottest day ever in September. This mark was tied September 4, 1988.
Milwaukee, WI (1988)
Hottest summer on record. Six days of 100 degrees or greater and 36 days of 90 or above. Average temperature of 73.8 beat the old record of 72.8 set in 1921 and 1955. The normal average tempera- ture for a summer in Milwaukee is 68.3 degrees.
Washington Co., IA (1897)
Hail fell and drifted in piles 6 feet deep in Washington County.