Heat wave sweeps across the US

Unhealthy levels of heat and humidity are encompassing much of the eastern half of the U.S., according to NOAA's National Weather Service, as a persistent heat wave continues its grip on the central U.S. while expanding into the East.

According to NOAA's National Weather Service, approximately 132 million people in the United States are under a heat alert (Excessive Heat Warning or Watch or Heat Advisory) as of Friday morning.

Temperatures in the 90s to near 100 degrees will feel as hot as 115 degrees or higher when factoring in the high humidity. Record high temperatures are likely to be set in some locations — adding to the more than 1000 records that have been set or tied so far this month.

The massive heat wave that has been gripping nearly half of the nation this week is certainly taking its toll. There have been as many as 22 heat-related deaths as of Thursday, according to CNN. Hospitals have been filling up with thousands of patients suffering from heat-related illnesses. In addition to being strenuous on people, the heat wave's effects have been far-reaching.

Many of the all-time high temperature records in the Northeast were set during the Dust Bowl era with several occurring on dates during the blistering summer of 1936. In a number of other locations, the nasty heat waves during July 1966 and August 1918 set the marks to beat. Elsewhere, the all-time list is scattered about various decades through the past century.

AccuWeather.com RealFeel® temperatures will be significantly higher than the actual temperatures. In some cases, the RealFeel will top 110 degrees. While similar to the apparent temperature and heat index, the RealFeel temperature incorporates a half-dozen or so additional variables and gives a more accurate "how it really feels" temperature.

Relief is coming to the Northeast in a gradual sense over the weekend into next week. However, no real relief is in sight for the South Central states. (…)

Daily U.S. Extremes past 24 hours

High humidity along with hot temperatures is making this week's heat wave in the central and eastern U.S. especially unhealthy. The dew point temperature is a measure of how much moisture is in the air. With dew points in the 60s, the air may be considered uncomfortable and in the 70s it becomes oppressive by diminishing a body's ability to sweat. In only rare cases will the dew points reach the 80s in the U.S. This movie shows average daily dew point data from the NAM model from July 18 through July 24, 2011.

A shroud of high pressure has taken a foot-hold over the U.S. from the Plains to the Northeast, and with it has brought temperatures well into the 90's and 100's for half of the country. This animation shows the predicted daily high temperatures from NOAA's high resolution North American Model (NAM) from July 13-21, 2011.