Meteorologists are growing increasingly confident that El Nino is brewing — but that doesn't mean they know what kind of weather it might bring Maryland.
The climate phenomenon that brings unusually warm water to the Pacific Ocean off South America with weather repercussions that echo globally is showing signs it may develop later this year.
Climatologists last week predicted greater than 65 percent odds El Nino will develop this summer, up to 80 percent by late fall. Some speculated it could be the strongest in years.
While El Nino is known by many for spurring weather disasters around the globe, it often doesn't do so, meteorologists said.
Still, it could mean another snowy season in Maryland next winter. But before that, it could weaken the summer and fall hurricane season.
Unlike elsewhere in the country and world, El Nino's effects are imprecise and unpredictable in Maryland, despite the hysteria the term can incite, climate researchers said.
"It is a very strong signal, but … in our area the signal is pretty quiet." said Konstantin Vinnikov, acting state meteorologist and a senior research scientist in the University of Maryland department of atmospheric and oceanic science.
The "signal" that climate researchers watch closely is water temperatures along the Equator in the Pacific Ocean, just west of South America.
And they are rising. The latest monthly report from the U.S. Climate Prediction Center released Thursday increased the likelihood of El Nino's occurring this summer from the 50/-0 chance it called for in April.
During normal, or so-called "neutral," conditions — when there is neither an El Nino nor its counterpart, La Nina — warmer waters blown by trade winds pool off the coasts of Australia, Papua New Guinea and Indonesia. That warm water evaporates and rises to create storms and heavy rain.
But when those trade winds weaken, or even reverse, climatologists note that an El Nino may be developing. A conveyor belt of mild, moist air that normally sloshes the warm waters west instead reverses course, allowing them to flow back to the central and eastern Pacific.
Following that warmth across the ocean are the massive storm clouds that rise out of the warm waters, which is what disrupts global weather patterns. That moist air is key energy in developing weather systems.
"When you change the distribution of heat sources, you change the distribution of energy, which tends to readjust the whole system," said Raghu Murtugudde, an oceanic and atmospheric sciences professor at the University of Maryland, College Park.
The shift of that moisture can mean droughts and wildfires for parts of Southeast Asia and Oceania and winter flooding and mudslides for Peru and Ecuador. It can stir a more active tropical cyclone season in the eastern Pacific.
El Nino is known for flattening the jet stream in a way that sends it through the moist central Pacific and straight across the lower third of the United States, funneling wet weather across southern states. That can lead to drier-than-normal weather in the Northwest, extra rain for the arid Southwest, and wet, cool weather for the Southeast.
But Maryland lies somewhat on the edge of that trend, making it more difficult to draw long-term conclusions based on an El Nino forecast. The region's geography between mountains and ocean, with the Chesapeake Bay in the middle, also prevents more dramatic climate fluctuations.
"For better for worse, Maryland is in kind of a lucky spot because we get moderated," said Eric Hohman, assistant state climatologist.
It's difficult to predict climate trends in the state beyond about two weeks out, Vinnikov added.
If there is one thing Marylanders associate El Nino with, however, it's snow.
An analysis by the National Weather Service's Baltimore/Washington forecast office shows that while about 18 inches of snow falls in an average winter in Baltimore, closer to 27 inches fall in an El Nino year. When the El Nino is considered to be of moderate strength, the average surpasses 30 inches, more than under either weak or strong El Nino events.
The record-breaking 77 inches of snow that fell in winter 2009-2010, for example, came during a moderate El Nino, the last one to occur. So did the third and fourth snowiest winters, 2002-2003 and 1963-1964. But the second-snowiest Baltimore winter, 62.5 inches in 1995-1996 came during La Niña, known for mild winters here.
Heavier snow in the Mid Atlantic states frequently is driven not just by the band of moisture El Nino brings, but also by the presence of what is known as a "blocking high" over Greenland, a pressure system that steers weather systems up the East Coast in storms known as nor'easters.
But there is no proven link between El Nino and blocking highs, said Huug van den Dool, a Climate Prediction Center meteorologist. So an El Nino doesn't always mean more snow.
In the summer and fall, El Nino does reduce the chances of tropical storms and hurricanes striking the Atlantic coast as it increases wind shear, when wind speeds differ at varying altitudes. That tends to spread storms' heat energy over a larger area, making them less intense.
A hurricane season forecast from the Tropical Meteorology Project at Colorado State University released last month found a 35 percent chance of a major hurricane striking the U.S. coastline, below a 52 percent average chance over the past century.
While climatologists' forecasts show an El Nino to be a strong likelihood, there is also a chance the trends will fizzle. The globe was placed on El Nino watch in 2012, and odds climbed as high as 75 percent, but that El Nino never came to be, Climate Prediction Center meteorologist Michelle L'Heureux wrote Thursday in a commentary on RealClimate.org.
Even if the development continues, government forecasters caution that, while El Nino has become synonymous with major disasters among lay weather watchers, the disasters often don't occur.
Among a list of El Nino misconceptions on the National Oceanic and Atmospheric Administration's Climate.gov website: that El Nino has only negative impacts, causes more disasters than normal, stems from climate change and can be held directly responsible for specific storms.
Some climatologists are betting on a strong El Nino, but acknowledge that there is still much to be understood about how interrelated global climate factors influence its development.
"It may be a better event than we have seen in a couple of years, so we are all very interested to see how this is playing out," van den Dool said. "Nothing is entirely certain or nothing is playing out perfectly to scenarios we have seen before. It's always somewhat different."