United States

As summer officially begins, dangerous heat is blasting the East.

A ridge of high pressure took shape across the Great Lakes region on Tuesday, the last full day of spring. Afternoon highs soared into the low to middle 90s in Milwaukee, Chicago, Detroit, Indianapolis and Louisville. On Wednesday, the East coast joined the sauna.

The heat is nothing new in this part of the country. All of the aforementioned cities have recorded at least two 90-degree readings so far in 2012, while Detroit has reached the mark six times.

According to Expert Senior Meteorologist Alex Sosnowski, "As of Wednesday, Chicago has hit the 90-degree 13 times times with St. Louis reaching the mark 18 times so far in 2012."

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Interestingly, Atlanta, Ga. has had only 4 days of 90-degree temperatures thus far.

As the ridge shifts eastward, places much less accustomed to these high thermometer readings in the coastal Northeast will swelter into Friday.

Beachgoers flock to the water at Coney Island during a heat wave, Wednesday, Aug. 2, 2006, in the Brooklyn borough of New York. (AP Photo/Jason DeCrow)

Cities as far north as Boston and Syracuse are forecast to break the 90-degree mark through Thursday. Pittsburgh, New York City, Philadelphia and Baltimore among others along the I-95 corridor are also expected to receive a harsh welcome to summer.

Wednesday featured the first 90-degree reading of the year for many cities. The swelter brings a noticeable change from the cool, overcast days that have dominated the last quarter of spring for much of the East.

Unfortunately, the high temperatures in the mid-Atlantic and Northeast will also be accompanied by high humidity (dew point temperatures in the upper 60s and lower 70s). This cocktail, combined with sunshine, wind speed and other factors will result in AccuWeather.com RealFeel® temperatures at or above 100 degrees during the afternoon.

Due to the high electricity demand with air conditioners running, the New York Power Authority has activated the Peak Reduction Program to lower electricity use in New York City. According to the NYPA, the program "involves commitments by the City of New York and other NYPA governmental customers to lower electricity use at more than 80 locations in the five boroughs, such as subway stations, public schools, City University of New York buildings and police facilities."

According to the Associated Press, several people had symptoms of heat exhaustion at the North Bergen High School graduation ceremony on Wednesday.

Some relief will be found in the form of pop-up afternoon and evening thunderstorms, as well as local waterway breezes. However, any storms will be spotty and isolated. Any sea, bay or lake breeze will wane in the evening hours.

Cooler, less humid air is coming, but not until Friday evening along the I-95 corridor. The end of the heat may be marked by powerful thunderstorms.

In the wake of a cool front, the heat has broken in Chicago and St. Louis Thursday.