JOPLIN, Mo. — A tropical climate pattern thousands of miles away in the equatorial region of the Pacific Ocean could make this winter warmer than normal for the Joplin area, according to a new winter outlook by the National Oceanic and Atmospheric Administration.

At the same time, new research is showing that the La Nina/El Nino climate pattern might now be used to portend outbreaks of severe weather in the lower 48 states.

The new research was triggered by the violent tornadoes that struck Tuscaloosa, Ala., and Joplin last year. In all, the 2011 tornado season claimed 538 lives, including 161 in Joplin.

The research, published in the Journal of Climate, shows a connection between a particular pattern of sea surface temperatures in the Pacific and large outbreaks of violent tornadoes during April and May in the lower 48 states.

The research was led by Sang-Ki Lee, with the University of Miami and NOAA. Lee’s research focused on “trans-Nino,” an ocean configuration that occurs during the transition phase as an El Nino or a La Nina event begins or ends.

A trans-Nino features cooler-than-average sea surface temperatures in the central tropical Pacific, and warmer-than-average sea surface temperatures in the eastern tropical Pacific. That alignment was present in seven of the top 10 extreme tornado outbreak years from 1950 to 2010. That configuration also occurred in 2011.

Lee said, “The number of intense tornadoes during these worst outbreak years, those rated as an EF-3 to EF-5, was nearly double the number in other years.”

Historical data allowed researchers to determine that trans-Nino was active in the three deadliest years for tornadoes — 1925, 1936 and 1917 — before tornado counting occurred.

The trans-Nino pattern, Lee said, favors a jet stream that promotes the clash of cold/dry air from Canada and warm/humid air from the Gulf of Mexico. It also favors atmospheric wind shear, a key factor in tornado formation.

“We were motivated by the 2011 tornado events, including Joplin, to see if there were any papers showing any connection between climate patterns and tornadic activity in the U.S.,’’ Lee said. “What we found was not conclusive or statistically insignificant.’’

The research, according to Lee, could help weather forecasters develop methods to make long-range and seasonal projections about the probability of major tornado outbreaks in the U.S. The projections would be like the annual hurricane prediction forecast that is now issued before the hurricane season.

Lee said trans-Nino helps create the conditions favorable for tornadoes, but it cannot explain why and where most tornadoes form.

“It’s dangerous to try to explain all the tornado outbreak events by the impact of climate,” he said. “You must consider that much of it is due to normal atmospheric variability.’’

Lee said work began last month on a system that could produce a tornado outbreak forecast. He said it is not clear yet how long it will take to develop or whether one might be ready before next spring.

“But that is the goal,’’ Lee said. “We want to issue a tornado outbreak forecast that will be a lot like the hurricane prediction forecast. We would look at the climate patterns that exist and forecast the probability of severe tornado outbreaks.’’

That forecast would be helpful, said Keith Stammer, head of emergency management for Joplin and Jasper County.

“If such a prediction model could be developed, it would be very important to emergency management. It would enable those of us in emergency services — police, fire, ambulance, health and public works — to ramp up our pre-event education to our citizens.

“It could also help us pre-position resources for a more rapid response, and staff and supply our post-event resources.’’

The forecast would not be specific in terms of actual events, Lee said, “but we could tell people that conditions do or do not favor severe tornado outbreaks.’’

In an ironic twist, an unexpected development in the La Nina/El Nino climate pattern is responsible for causing a change in this season’s hurricane prediction forecast. That change also is responsible for Joplin’s winter outlook favoring warmer-than-normal conditions.

In recent years, NOAA hurricane forecasts have had an accuracy rate of 95 percent. In May, NOAA predicted there would be nine to 15 named storms this year. In August, the prediction was changed to 12 to 17 named storms.

Forecasters in May predicted an El Nino, characterized by warm surface temperatures in the Pacific Ocean, would develop and retard hurricane formation. An El Nino pattern can produce winds that stream eastward, disrupting the weather patterns that give a developing hurricane its strength.

That didn’t happen. Because of that, it’s been one of the busiest hurricane seasons on record, with 19 named storms so far this year. Ten of them have become hurricanes.

The fact that an El Nino has not formed is the reason why this winter might be warmer than normal.

Mike Halpert, with NOAA’s Climate Prediction Center, said, “It did not shift patterns in early September. It’s cooled back towards neutral. We have not written an El Nino off yet. It could warm up in the next couple of months.’’

It takes three to four months for a quick transition from a La Nina, which is cooler-than-normal sea surface temperatures in the Pacific, to the warmer El Nino.

Halpert said a La Nina ended in April and May. Conditions shifted to neutral to transition to an El Nino, but the El Nino did not materialize. Typically, a La Nina lasts nine to 12 months, while an El Nino will last 12 months.

“In an El Nino, the northern part of the nation is favored to be warm and the southern part cooler. La Nina is the opposite of that,’’ he said. “A La Nina also is more favorable for drought conditions over the U.S.’’

Halpert said, “The La Nina cycle forms the background for our winter outlook. It’s our No. 1 forecast tool.’’

The winter outlook suggests that areas ravaged by extreme drought over the past year are unlikely to see much relief from drought conditions this winter.

Gene Hatch, a climatologist with the National Weather Service forecast office in Springfield, said local farmers could see the drought intensify.

“If the lack of water recharge persists through this winter, we could start next spring’s growing season with a deficit,’’ he said.

Winter forecast

According to NOAA’s winter outlook, the odds favor:

• Higher-than-average temperatures in much of Texas, northward through the Central and Northern Plains and westward across the Southwest, the Northern Rockies, and eastern Washington, Oregon and California, as well as the northern two-thirds of Alaska.

• Lower-than-average temperatures in Hawaii and in most of Florida, excluding the Panhandle.

• Drier-than-average conditions in Hawaii, the Pacific Northwest and Northern California, including Idaho, western Montana, portions of Wyoming and Utah, and most of Nevada.

• Drier-than-average conditions in the upper Midwest, including Minnesota, Wisconsin, Iowa and northern Missouri, and the eastern parts of North and South Dakota, Nebraska, Kansas and western Illinois.

• Wetter-than-average conditions across the Gulf Coast states from the northern half of Florida to eastern Texas.