PHILADELPHIA (CBS) — Heat and a warm feeling may depend on who you ask and when you ask. Are we talking about relatively high temperatures in winter or hot summer temperatures?
The unique nature of how people experience heat makes it difficult to pin down an exact definition of a heat wave, but here’s a rough breakdown with a little more detail when it comes to warnings issued when temperatures rise and could become dangerous to the general population. population.
What is a heat wave?
A heat wave is broadly defined as a period of abnormally warm weather that typically lasts more than two days. Although this definition is quite broad, this must be because communities in different parts of the country or world can tolerate heat in different ways.
Regions more accustomed to 90-degree temperatures, such as Florida and the desert Southwest, may not consider a week in the summer with temperatures in the mid-90s to be a heat wave. While these temperatures are arguably hot, they are close to the temperatures they typically experience during the summer months.
If the same temperatures were experienced in the Northeast or parts of the Midwest, it would certainly be considered a heat wave. The normal high temperature in the Philadelphia area peaks at 88 degrees in mid-July. For this reason, it can be considered a heat wave if temperatures remain above 90 degrees for more than two days.
That said, heat waves can occur with or without humidity, which ultimately affects heat index values and how the temperature actually feels.
For this reason, the National Weather Service issues heat warnings based on what the heat index is expected to be, rather than what the actual temperature will be.
Heat advice
Just as different regions define heat waves differently, the criteria for some weather warnings, especially temperature-related warnings, also vary. Even here in the broader Delaware Valley, the criteria for issuing a heat advisory depends on location.
A heat advisory means that people can suffer from heat if no precautions are taken. Issuing a heat advisory is important to make the public aware that these precautions must be taken. Heat advisories are also used to trigger other actions and regulations, such as no evictions, no power shutoffs, changing outdoor work requirements, etc.
Covering much of Philadelphia’s urban corridor, covering New Castle County in Delaware, eastern Chester County, Delaware County, Lower Montgomery County, Philadelphia, Lower Bucks County in Pennsylvania and Mercer County, northern Burlington County, Camden County and Gloucester Counties in New Jersey will be issued a heat advisory when the heat index is expected to be between 96 degrees and 104 degrees for two consecutive hours through June 30. After June 30, the criteria for a heat advisory for that same area is when the heat index is expected to be between 100 degrees and 104 degrees.
For the Lehigh Valley, including Lehigh, Northampton Counties and Carbon and Monroe Counties in the Poconos, as well as the southern half of Burlington County in New Jersey, a heat advisory will be issued when the heat index is expected to be between 100 degrees and 104 degrees lie. two consecutive hours, at any time of the year.
Atlantic, Cape May, Cumberland and Salem Counties, New Jersey, as well as Kent and Sussex counties in Delaware will be under a heat advisory when the heat index is between 105 degrees and 109 degrees.
Excessive heat watches and warnings
When conditions are forecast to be warmer than the above criteria, the next level of heat alerts will be activated: Excessive Heat Warnings and Warnings.
An excessive heat warning means that some people could be seriously affected by heat if precautions are not taken. According to the National Weather Service, studies in Canada, Europe and the U.S. have shown that mortality begins to increase exponentially as heat increases or remains above a heat index of 104 degrees.
In addition to increasing public awareness, issuing an excessive heat alert will alert hospitals and officials to take certain actions to prepare for and respond to an increase in emergency calls and activate programs to help the elderly and to control housebound people.
In some cases, cooling centers may be open or designated and donation programs for fans and air conditioners may be activated. As in the case of an advisory, certain rules may change, such as turning off people’s electricity, evictions and external work requirements.
The criteria for an excessive heat warning for most of Philadelphia, including the Lehigh Valley and the Poconos, is when the heat index is expected to be 105 degrees or higher for two hours or more. Atlantic, Cape May, Cumberland and Salem Counties, New Jersey, as well as Kent and Sussex counties in Delaware will be under an excessive heat warning when the heat index is forecast to be 110 degrees or higher.
An Excessive Heat Warning will be issued when Excessive Heat Warning Criteria are expected within the next 48 hours.
