Lightning and heavy rain slammed the greater Philadelphia region Tuesday leading to power outages across the area.

Flash Flood and Severe Thunderstorm warnings were issued for parts of the area. Fire officials say lightning started a fire at a school in Bellmawr, New Jersey. Witnesses also say lightning may have started a large fire at an apartment complex in Edgewater Park, New Jersey.

The storms caused widespread outages. PECO reported 37,406 customers without power shortly before 10:30 p.m. The number of outages was down to 6,000 by 9:15 a.m. Wednesday.

The storms and outages added to the already treacherous heat that swamped the Delaware Valley and southern New Jersey for the last few days. An NBC10 First Alert remained in effect for Philadelphia through Wednesday as humid, hot temperatures were expected throughout much of the Wawa Welcome America celebration on July 4th.

The "urban heat island" makes the city much hotter than other areas and doesn't allow it to cool as fast as the suburbs.

Afternoon temperatures Tuesday soared into the mid 90s, but it felt like it was in the triple digits with high-humidity levels.

In response to the soaring temperatures, Philadelphia issued a heat health emergency warning that will last through Wednesday evening.

The declaration of a heat emergency activates the city’s heat programs, including the Philadelphia Corporation for Aging’s Heatline, extended hours at select Free Library locations that have been designated as Cooling Centers, home visits by special field teams, enhanced daytime outreach for the homeless, and an annual reminder to the public to look in on older friends, relatives, and neighbors.

Conditions are dangerous for anyone, but particularly for the elderly, infants and those with health issues. Limit your activity outdoors during the peak heating of the day and hydrate with non-alcoholic liquids frequently.

Parents should avoid leaving their kids inside the car without air conditioning. An average of 27 children die each year after being left unattended in a vehicle, according to safety advocacy group Kids and Cars.

As the heat wave reaches its peak, experts are stressing their advice on staying safe in the dangerous heat. Experts recommend to drink even when you’re not thirsty to stay hydrated, reapply sunblock, limit your hours outdoors and much more.

The Tredyffrin Township Police Department is giving out free stickers to help parents avoid that kind of tragedy.

According to @KidsAndCars, an average of 37 children die each year after being left unattended or forgotten in hot cars.



Even one is too many.



Designed by our Officers, these reminder stickers are now available FREE OF CHARGE; more > https://t.co/BM6DJAhX99 pic.twitter.com/sdIfFTdTC8 — Tredyffrin Township Police (@The_TTPD) June 18, 2018

The cause behind the heat is a huge high pressure system that has been delivering intense heat to the south and southwestern United States. This "heat dome" will shift east and cover most of the East Coast, including our area into the work week.

It’s the balance transfer that went bad. Our viewer says his attempt to save money, left him owing hundreds of dollars. He contacted Harry Hairston and NBC10 Responds.

With feels-like temperatures around or above 100 degrees, outdoor activities may be dangerous. Particularly, elderly, children and those with respiratory problems (since air quality degrades in high heat) should be cautious outside. Everyone should limit time outdoors, especially in the afternoon.

A suspect surrendered to Philadelphia Police after a deadly stabbing inside an Olney home.

Visiting shopping centers or public buildings with air-conditioning are good ideas. The Delaware beaches & Jersey Shore will have a cooling sea breeze during the hottest afternoon hours, which will bring major relief to those areas. Ocean water temperatures have climbed into the lower 70s, making the water extra inviting.

Independence day will be hazy, hot, and humid, but not quite as hot or humid as early in the week. Still, highs in the low 90s plus high humidity will make it feel like mid to upper 90s, especially in Philadelphia.

Increasing clouds Friday with showers and thunderstorms will keep us from warming into the 90s, bringing an end to the heat wave. Over the weekend, it will be warm and sunny with highs in the 80s.