TheWeatherStation's Blog

There are two key factors that will continue to affect our weather over the next couple of months. It’s the NAO and La Nina. The winter storms we’ve experienced so far this winter have been typical of these conditions, snow changing over to ice and rain. The good news is that we expect this trend to continue for the rest of the winter.

WATCH THE SPRING OUTLOOK VIDEO

First factor, the NAO (North Atlantic Oscillation) is an atmospheric indicator helping us to determine how much snow we get or don’t get. When the NAO is negative, we get more snow. An example would be the winter of 1995-96. Philadelphia hit an all time snow record of 65.5” of snow. When the NAO is positive, the snowfall tends to be below average. This year, so far we stand at 6.2” of snow which is well below the average.

The second factor: La Nina is characterized by unusually cold ocean temperatures in the Equatorial Pacific. This results in generally a milder winter with brief episodes of arctic air.

With the combination of these two factors to continue into March. The outlook remains the same with a trend towards less snow and more in the way of ice. As we head into spring, La Nina should keep you guessing on what to wear. A typical La Nina spring can bring rollercoaster conditions with periods of cool & wet interrupted by warm and dry spells. Overall the temperatures should average slightly above normal.

You may be eager to use the parks around Philadelphia. But don't put your coats away just yet. It could be well into April before the temperatures will be mild enough to enjoy the outdoors on regular basis. I have always used Tax Day (April 15th) as the official end to winter. This is especially true during a La Nina spring as cool, rainy bouts tend to put a damper on any spring flings.

May gives us a taste of what's ahead for the summer. And if this La Nina year follows others in years past... the summer could produce an active more intense hurricane season -- one that may bring high winds to the now calm New Jersey shore.

One of those La Nina years was in 1999 when Hurricane Floyd moved through the Atlantic Ocean -- up from the Bahamas -- then paralleled the northeast coast.

Flooding and high winds: just some of the devastating effects Floyd left behind in the Lehigh and Delaware Valleys.

La Nina allows the hurricane intensification process to be uninhibited -- leading to more intense hurricanes.

1985: Gloria - Cat. 4 with 145 mph winds

1988: Gilbert - Cat. 5 with 185 mph winds

1995: Opal - Cat. 4 with 150 mph winds

1999: Floyd - Cat. 4 with 155 mph winds

Here are some of those intense storms from past La Nina years:

In 1985... There were three major storms... Including Gloria -- a Cat Four.

Three years later... Three major storms... Including Gilbert -- a Cat Five hurricane.

In 1995... Hurricane Opal was among the four major storms.

Then most recently Floyd in 1999.

You've probably heard of El Nino -- the opposite of La Nina.

El Nino stifles the hurricane intensification --- that's why we generally see fewer storms during El Nino years.