August 2, 2004 — Everyone wants to know, “What will the weather be like tomorrow?” But the NOAA Climate Prediction Center has taken this a step further and is able to predict what future U.S. temperature and precipitation (i.e., climate) may look like up to a year in advance? The product, called the “U.S. Seasonal Outlook,” offers enormous potential social and economic benefits and is part of the NOAA National Weather Service suite of official weather and climate products.

Climate vs. Weather Forecasting
“Climate forecasting is in its infancy when compared to weather forecasting,” said Edward O’Lenic, chief of climate operations at the CPC. “The first official U.S. government weather forecasts were published in 1871, while the first U.S. Seasonal Outlook was not issued until 1982,” he added. Furthermore, only recently (in 1995) were the climate outlooks extended (long-term) out to one year.

Unlike regular weather forecasts that predict specific day-to-day changes, the U.S. Seasonal Outlook attempts to predict — using probabilities — whether the average temperature and precipitation will be above-, below- or near-normal over a given time period and geographic region. In other words, U.S. Seasonal Outlooks provide insight into longer-term expected trends, such as drier/wetter or colder/hotter than normal conditions for a season in a particular region.

Benefits and applications of the U.S. Seasonal Outlook
Despite the fact that the CPC’s long-term U.S. Seasonal Outlooks, have been around for less than a decade, the importance and demand for this product is quite evident. Weather and climate sensitive industries directly and indirectly account for approximately 25 percent of the nation’s gross domestic product or $2.7 trillion. Because these industries need to anticipate future climate conditions, the U.S. Seasonal Outlooks aids them in their planning and purchasing decisions.

If interpreted and used properly, long-range forecasts can greatly aid in the management of water, fires, cattle, agriculture, utilities and energy. Other industries and applications that benefit from long-term seasonal outlooks include transportation, manufacturing and retail businesses, recreation, weather derivatives/futures markets, emergency management and the health and travel industries. The further out NOAA is able to predict future climate conditions, the more time these entities have to plan ahead for the benefit of both the economy and society as a whole.

Generating a U.S. Seasonal Outlook
U.S. Seasonal Outlooks are based on long-term climate trends and a variety of forecast tools (which run the gamut from relatively simple statistical techniques to extremely complex dynamical ocean-atmosphere coupled models and composites based on the phase of the El Niño/Southern Oscillation). These tools often have varying degrees of certainty or success (determined by comparing older forecasts to actual weather and climate observations) depending on the geographical location and time of the year. The NOAA CPC also thoroughly vets each U.S. Seasonal Outlook with other scientists before it is released to the public. In fact, one of the most important parts of the forecast process is a discussion of the various tools used in producing the outlook, which involves scientists from other NOAA offices (including the NOAA Climate Diagnostics Center in Boulder, Colo.), as well as from universities and the International Research Institute for Climate Prediction (a private, Columbia University-based non-profit organization partially funded by NOAA). Close collaborations such as these are essential to optimizing the objectivity and accuracy of the outlooks.

About the U.S. Seasonal Outlook
The U.S. Seasonal Outlook, produced in both text and graphical form, gives the probability that total precipitation and average temperature will be above-, below- or near-normal (i.e., average over past 30 years) during three-month seasons.

Each month, on the third Thursday of the month at 8:30 a.m. ET, a new set of seasonal forecasts (for each of the twelve possible combinations of adjacent three calendar month “seasons”) are posted on the internet. Because the season closest in time to the release date is about two weeks away, its “lead-time” is half a month. The second season in the series would be an additional whole month in the future, and therefore has a lead-time of one and a half months. This continues out to the 13th season, which has a lead-time of 12.5 months. The outlook for each successive/prior lead time overlaps the prior/successive one by two months. This overlap makes for a smooth variation from one map to the next (Click here for a schedule of issuances for 2004). Valid times for seasonal outlooks are indicated by 3-letter abbreviations (e.g. JFM = January-February-March; AMJ = April-May-June; etc.). There are two maps for each of the 13 leads, one for temperature and one for precipitation, for a total of 26 maps. A monthly outlook is also prepared at the same time as the seasonal outlooks.

The maps of the Official U.S. Seasonal Outlook represent probabilities that temperature and precipitation will be above, below or average for the season. Specifically, they are prepared for average temperature and total accumulated precipitation in three categories. These are below-, near- and above-normal for temperature and below-, near- and above-median for precipitation.

At any given location on a U.S. Seasonal Outlook map, the sum of the odds for the three categories is equal to 100 percent. Areas where the odds for the three categories are even, (that is, equal to 33.3 percent each) are labeled as "EC", which stands for "equal chances." Areas where the odds of one of the categories rises above 33.3 percent are shown as regions covered by concentric probability contours whose values increase, starting with 33.3 percent, then 40 percent, 50 percent and so on. Although it is not shown explicitly on the map, the increase in the values of the probability contours for the favored category are always compensated for by a decrease in the value of the probability of the opposite category. For example, a point on the map that has a 40 percent chance of above-normal temperatures also has a 33.3 percent chance of near-normal temperatures and a 26.7 percent chance of below normal temperatures (note how these three numbers add up to 100 percent).

Interpreting a U.S. Seasonal Outlooks
The example to the right shows the U.S. Seasonal Temperature Outlook issued on June 17, 2004 (Click on NOAA image for a larger view of this temperature outlook). This outlook can be interpreted to mean that there is an enhanced probability of above normal temperatures in both the western and eastern states, and below normal temperatures in Texas and the Great Lakes region. It is important to note that the numeric values on the outlook are not temperatures, but probabilities that the average temperatures over that season are anticipated to be above or below the 30 year norm (average) for that region. Specifically, the number 40 in the western states (i.e., red area labeled with an A) means that there is a 40 percent chance of above normal temperatures, a 33.3 percent chance of normal temperatures and a 26.7 percent chance of below normal temperatures. Likewise, the number 50 next to it means that this region can expect a 50 percent chance of above normal temperatures, 33.3 percent chance of normal and 16.7 percent chance of below-normal temperatures. The same can be said for the blue regions labeled with a B, only they represent number values for enhanced probabilities of below-normal temperatures. Areas labeled “EC” mean that there is an equal chance of above-, near-, or below-normal temperatures in this region. A similar approach can be used to interpret the U.S. Seasonal Precipitation Outlook issued on June 17, 2004 (See figure to the left. Click on NOAA image to the left for a larger view of this precipitation outlook). Because there are three categories describing each geographic area, this is known as a “three-class” system.

In 2003, the CPC introduced a new, easier to interpret, experimental “two-class” system representing above and below-normal categories only (i.e., the near-normal category was eliminated). In this case, the long-term likelihood of the two categories is a half or 50 percent each. Thus, interpreting the same U.S. Seasonal Temperature Outlook issued on June 17, 2004, using a two-class system, a numeric value of 55 in the western states ((i.e., red area labeled with an A) represents a 55 percent chance of above normal temperatures and a 45 percent chance of below normal temperatures. Likewise, the numeric value of 60 next to it means that these regions can expect a 60 percent chance of above normal temperatures and a 40 percent chance of below normal temperatures, etc. A similar approach can be used to interpret the U.S. Seasonal Precipitation Outlook issued on June 17, 2004 in a two-class system.

Relevant Web Sites
NOAA CPC MISSION

NOAA National Climatic Data Center

Weather vs. Climate

Future Forecasts

Predicting the Future

Color Interpretation of U.S. Seasonal Outlooks

Media Contact:
Carmeyia Gillis, NOAA Climate Prediction Center, (301) 763-8000 ext. 7163