Heat and severe weather are in the forecast Tuesday for the Northeast.
CNN  — 

A wide range of weather is impacting the Northeast on Tuesday, ranging from extreme heat to severe storms in the afternoon.

A severe thunderstorm watch is effect until 8 p.m. for parts of the Northeast and New England where severe weather, including damaging wind and large hail, is possible.

Heat advisories cover around 40 million people in the region, including in Philadelphia, New York and Boston, where the heat index will surpass 100 degrees.

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Hot and muggy midweek

A brief cooldown for the Northeast provided for a nice Fourth of July holiday weekend, but the heat is ramping back up.

Heat advisories are in effect through Wednesday for New York, as temperatures soar into the middle of the week. Heat indexes could be as high as 100 to 103 degrees in the area.

“A Heat Advisory is issued when the combination of heat and humidity is expected to make it feel like it is 95 to 99 degrees for two or more consecutive days, or 100 to 104 degrees for any length of time,” according to the National Weather Service in New York.

Eight states across the Northeast have heat advisories in effect at least through Tuesday, with some extended through Wednesday.

Heat advisories are in place across the Northeast.

High temperatures will be in the 90s, but combined with the high humidity, it will feel much hotter. Dew points in the high 60s make it feel muggy and elevate the risk of heat-related illness.

“When the atmospheric moisture content (i.e. relative humidity) is high, the rate of evaporation from the body decreases. In other words, the human body feels warmer in humid conditions,” the weather service says.

The heat index is directly related to temperature and relative humidity, thus making heat advisories necessary for the Northeast.

Afternoon severe storms

Heat isn’t the only weather risk, as the Storm Prediction Center has issued a slight risk for some areas of the Northeast and southern New England.

A slow-moving front will head from the Great Lakes across the Northeast over the next few days, bringing with it a threat for severe weather. A slight risk for severe weather, level 2 of 5, extends from New Jersey through much of New York and into southern New Hampshire and Vermont.

“A couple of bands of storms are likely to evolve with strong to locally severe gusts (50-60 mph) capable of wind damage,” said the Storm Prediction Center in its forecast discussion.

A slight risk has been issued by the Storm Prediction Center for Tuesday.

Daytime heating and high moisture levels will lead to the storm development midday, increasing in coverage throughout the afternoon.

“Some of the storms this (Tuesday) afternoon will likely be strong to severe with damaging wind gusts and torrential downpours,” said National Weather Service Boston/Norton, Massachusetts.

Excessive rainfall could lead to localized flooding concerns in low-lying areas and on streets across the region. The Weather Prediction Center has issued a marginal risk for excessive rainfall in the area due to the potential to see over an inch of rainfall per hour in some areas.

“This activity is likely to move over the highly urban corridor from Connecticut to New Jersey where isolated flash flooding will be possible into the early to mid-evening hours,” warns the prediction center.

A marginal risk is in place for the same region on Wednesday.

A marginal risk for severe weather has been issued for Wednesday.

“Isolated strong to severe storms capable of locally damaging wind gusts are possible on Wednesday across parts of northeast Pennsylvania into portions of the Northeast,” said the Storm Prediction Center.

Once the front makes its way farther eastward from the Great Lakes into the Atlantic by the end of the week, the severe threat for the region will diminish.