Wicked N.J. sky turns into storms

A severe thunderstorm approaches the state fair in East Rutherford in July of 2014.

(Saed Hindash)

NOTE: This story was published in June 2015.

New Jersey is potentially facing its most significant severe weather threat of the year Tuesday, just as the state enters peak thunderstorm season.

Forecasters say the atmosphere is expected to become a veritable powder keg for severe thunderstorms just in time for Tuesday afternoon's rush hour, with an unusually high amount of instability combined with abundant moisture in the atmosphere and a potent cold front expected to push through the area.

"When I see these kinds of levels ... I say 'whoa, that's a lot of energy," said Steven DiMartino, a meteorologist and owner of NJ NY PA Weather. "It's like having a lot of gasoline and one match. The more gasoline you have the larger the fire you're going to create when you light it."

Martino is referring to predicted levels of Convective Available Potential Energy, or CAPE, which is a measure of energy or instability in the atmosphere that a storm system has to feed off of. CAPE levels are predicted to be between 2,500 and 4,000 J/kg Tuesday afternoon, which is significant.

"Normally I'm looking for CAPE values around 1,000 to 1,200. When you start getting around 1,500, you're talking about the potential for a pretty widespread severe weather event," DiMartino said. "When you're talking about values over 3,000, that's the kind of thing you see in Oklahoma."

CAPE acts as the gunpowder for a severe weather event, and an approaching storm system -- in this case a powerful cold front -- acts as a match. There is also predicted to be vast amounts of moisture available for developing storms to tap into, meaning torrential rain and flash flooding are also possible.

The North American Forecast Model (NAM) predicts extremely high CAPE levels across NJ Tuesday afternoon.

The storms are expected to develop Tuesday afternoon, bringing a severe weather and flash flooding threat to the entire region.

Damaging straight-line winds are possible with these storms as well as some hail.

The possibility of a tornado cannot be ruled out, but forecasts suggest there will not be significant wind shear to be present, which helps to spin air in severe thunderstorms like a top and produce tornados.

However, the damaging wind threat could be significant, DiMartino said. When hot, moist air -- like what is predicted to be in place Tuesday -- is lifted high into the atmosphere during thunderstorm development, it cools quickly, becomes dense and rushes back to the ground. It can produce winds in excess of 60 miles per hour, which, when combined with torrential rains, can be a dangerous situation for anyone on the roadway.

DiMartino was quick to note that severe weather prediction is a tricky game. Just because the ingredients come together doesn't mean they will produce the expected outcome. Forecasters are urging state residents to pay close attention to weather outlets Tuesday, as conditions may change rapidly.

For example, storms explosively developing to the north or south of the state could suppress thunderstorm development in New Jersey. Quickly rising air ahead of thunderstorms has to sink somewhere else, and it is all a matter of where the line of storms sets up Tuesday.

New Jersey is just now entering the peak of severe weather season, which typically runs through July, according to data from the National Weather Service. While New Jersey has had plenty of rains in recent weeks, all but washing away previous drought fears, this marks the first widespread significant severe weather threat the state has faced in 2015.

The one positive to the situation -- once the cold front passes through, a return to cooler, less humid weather is expected. By the weekend, high temperatures may not escape the upper 70s across most of the state, a significant difference from the lower 90s expected prior to the thunderstorm threat Tuesday.

Stephen Stirling may be reached at sstirling@njadvancemedia.com. Follow him on Twitter @sstirling. Find him on Facebook.