'Hurricane’ Schwartz: El Nino returns

We've been waiting for its return for months, if not longer. It's called "El Nino," and it affects the weather worldwide -- sometimes for more than a year.  (for a weekend forecast, go here)

Background: What it Is

El Nino is the warming of the Tropical Pacific Ocean that can cover thousands of miles and many degrees of temperatures. The energy involved in warming an area that big that much is incredible. No wonder it has such far-reaching effects. Here's an illustration of the most recent ocean temperature changes -- the reddish band near the middle represents the El Nino:

The degrees are in Celsius, so it is showing anomalies of 1 to 3 degrees. An anomaly is the difference between the current reading and the long-term average (or normal). You'll notice that area extends from the coast of South America all the way to the Philippines.  That's more than 5,000 miles wide.

And the water temperatures under the ocean surface show even warmer water ready to move up to the surface, strengthening El Nino even more:

Some of that water is more than six degrees Celsius above normal -- that's a big increase, and spread over thousands of miles. If even some of that warm water makes it to the surface, this El Nino will become a pretty strong one.

And the forecast for the upcoming months is indeed for El Nino to strengthen.

The numbers on the left represent the El Nino index. When the ocean temperature anomalies over a large area reach 0.5, we have an El Nino. If the number gets to 1, it's considered a moderate El Nino. And if it goes above 1.5, it's considered strong. The computer model shown above suggests a number closer to 2, or even higher, which would clearly be a strong El Nino.

The strongest El Ninos ever recorded were …

1997-98 2.4

1982-83 2.2

1972-73 2.1

What a Strong El Nino Would Do

Since El Nino happens in the Pacific, the parts of the U.S. closest to it experience the major effects. That means California. It is in the midst of its worst drought ever recorded:

But the weather pattern changes triggered by El Nino will help tremendously. Why should we care? A lot of fruits and vegetables come from the "exceptional drought" area, so it has caused prices to go way up. But a strong El Nino sometimes brings too much rain to that area, with flooding as a result.

El Nino also affects the Atlantic hurricane season. The very warm Pacific leads to stronger winds high in the atmosphere. Those winds move over the Caribbean and Atlantic, leading to too much "wind shear," which either weakens tropical storms or doesn't let them form at all. Many strong El Nino years resulted in quiet hurricane seasons in the Atlantic. The 1997 and 1982 seasons were not active ones. This is why so many forecasts are for a relatively quiet Atlantic hurricane season this year (of course, all it takes is one to make it a bad season for some).

Worldwide, there is so much heat coming up from the sub-surface ocean that it affects overall temperatures on earth. It is no coincidence that 1988 was the warmest year, by far, up until recent years. A strong El Nino is likely to make 2015 the warmest year on record, perhaps by quite a bit. Let's see how that forecast turns out.

But What About Us?

The most important impact a strong El Nino would have on this area (aside from a lower hurricane risk) is a higher chance of much less snow than recent winters. That is, IF the El Nino is still strong by winter.

The three strongest El Nino years, mentioned earlier, gave us very little snow. Here are the numbers:

1998 0.8"

1988 11.2"

1972 Trace

That means the two least snowy winters ever recorded in Philadelphia just happened to be strong El Nino years.

We actually had a winter with no measurable snow? Yes -- that's not a typo. I actually started doing winter forecasts in 1997 because of the strong El Nino, and figured we'd have another winter with very little snow. I was right, and winter forecasting in Philadelphia began. No future years were that easy.

So, if you want a winter without much snow, and want lower prices for fruits and vegetables, root for El Nino to strengthen even more -- and to stay strong through winter.

Glenn "Hurricane" Schwartz

Chief Meteorologist

NBC10 Philadelphia