01:20 - Source: CNN
'El Nino' expected to impact winter weather patterns
CNN —  

Welcome rains could be on the way to drought-stricken California. But Boston, where the last of a 75-foot snow pile didn’t completely melt until July, should watch out – yet another snowy winter is possible for much of the eastern seaboard.

The National Oceanic and Atmospheric Administration’s outlook for winter, issued Thursday, points to a strong or even record El Niño through the winter.

El Niño – a warming of the eastern Pacific Ocean – began in March and has been steadily strengthening. It has already led to an extremely busy hurricane season in the Pacific, while contributing to a dud of a season in the Atlantic.

Forecasters anticipate even more impacts over the United States this winter, as El Niño is likely to generate a strong ridge of high pressure in the Northwest and Plains. This would will result in above-normal temperatures and below-normal precipitation.

Another likely result: A strong southern jetstream, which is likely to bring welcome rains to California, as well as heavy rains and possible flooding to parts of the Gulf Coast and Florida.

“We have more confidence in the forecast this year, compared to other years with the strong El Niño,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center. “El Niño is normally a positive for the U.S. in the winter. It can lead to milder than normal temperatures in the north, and beneficial rains to California.”

Temperature Forecast

Much of the country’s northern half is forecast to have above-normal temperatures, while much of the southern half is expecting below normal temperatures.

This could lead to a lower snow pack in the west, with rain falling in the mountains, where typically you would have snow.

If the forecast is correct, the weather would lead to lower heating costs in the Midwest and Northeast, and more snow and ice in the Southeast.

Precipitation Forecast

There are good chances for above-normal precipitation over the southern tier. This is particularly good news for California, still in persistent – and, in some cases, record – drought.

An active southern jetstream could lead to a steady stream of storms across the South. This could have wide-ranging impact, such as a higher severe weather and tornado threat for the Gulf Coast and Florida.

It could also bring snow to southern cities like Atlanta, Charlotte, and Raleigh, while also making conditions ripe for Nor’easters, which can bring big snows for many Northeast cities like New York City and Boston.

Dry conditions in the Pacific Northwest could exacerbate an already severe drought, while Chicago, Cleveland and Detroit may get a welcome break from Old Man Winter.

The growing El Niño

Last year, there was no strong signal to help forecasters make their winter outlook. This year’s strong El Niño makes it easier – it is expected to have a major influence on weather patterns not only in the United States, but globally.

History shows what El Niño commonly brings. This year’s El Niño is already strong and is getting stronger. The latest forecast shows that, this winter, El Niño could peak near or at record levels, with a 95% chance that it will continue through winter.

The benchmark El Niño year was 1997, which saw significant U.S. impacts. Mudslides in southern California, flooding in the Southeast, a big Northeast ice storm, and tornadoes in Florida highlighted the active winter of ’97-98.

California relief

If the forecast is correct, California could be the big winner.

The state, plagued by a record four-year drought, is in desperate need of rain and snow. NOAA’s outlook for this winter says there is a likelihood of above-normal rain amounts for southern California.

“The greatest impact on the drought in California, would be to have the heavy rain fall in the northern part of the states and in the mountains, but the best signal for El Nino is for heavy rain further south,” said Alan Haynes, a hydrologist with the California Nevada River Forecast Center.

How much rain would it take to nudge California out of the drought? The short answer is a lot.

NASA calculated at the end of 2014 that more than 11 trillion gallons of rain would be needed to end the drought, and the drought has only worsened since then.

A recent NOAA publication entitled “How deep of a precipitation hole is California in?” shows that the state would require as much as 200% to 300% of normal precipitation in the next year, depending on the area of the state, to eliminate the deficit.

“Our wettest year on record in California was in 1983, when we saw nearly twice the normal amount of precipitation. Even if this year has more rain than that, we wouldn’t get rid of the drought entirely,” Haynes said.

NOAA’s October-January drought outlook, also released Thursday, does call for some improvement over California’s southern half through January, but little change in the north.