On the same day, a high temperature of 91 degrees was recorded in Topeka, Kansas, and a heat warning I was issued.
Yes, but each National Weather Service (NWS) office has different criteria for heat warnings and excessive heat warnings that take into account the topography, weather, and possible effects of a region’s urban heat islands.
For example, Miami was very hot on Tuesday, but did not meet the technical requirements for a heat warning or warning.
To receive a heat notice, Miami must have a heat index of 108 degrees or higher for at least two hours. For an excessive heat warning, the heat index must reach 113 degrees or higher for at least two hours.
Florida winds
Tyler Mauldin, a CNN meteorologist who worked in Florida for almost 10 years, explains that the sea breeze plays a key role in temperature variability across the sun state.
“Florida’s climate is strongly influenced by the direction of the wind,” he said. “An offshore wind is a very hot wind for Miami, which is exactly what we had in place. It blocks the entry of the coldest air in the Atlantic. Add some dry air with dew points in the 1960s, and that’s a recipe for dangerous temperatures. “
Miami has not had just one hot day this year, but weeks and weeks of intense heat. In fact, seven of the 10 hottest weeks on record have occurred this year, and Miami’s high temperatures traditionally don’t peak until early August.
Excessive heat criteria vary
Again, it all comes down to different criteria. In Columbia, the heat index must reach at least 100 degrees to have a heat warning. In Minneapolis, a heat warning is issued when the heat index reaches 95 degrees.
Another criterion used by some offices of the National Weather Services, such as that of Minneapolis, is a measurement called a wet bulb globe thermometer.
The military has used this tool for decades. The wet bulb globe thermometer takes into account more details like the angle of the sun, the cloud cover and the wind speed. This is especially important to know if you are outside doing some kind of rigorous work, exercising, or monitoring youth sports events.
In Minneapolis, the criteria for a heat warning is a heat index value of 95 degrees or a wet bulb balloon reading of 86 degrees.
Philadelphia has its own heat bubble
Philadelphia has its own guidelines called Kalkstein Procedures.
Simply put, their research concluded that heat and humidity levels below the criteria that triggered a warning caused adverse effects in urban locations due to the presence of widespread asphalt and population density.
The NWS Philadelphia office not only uses different criteria for urban and rural locations, but also breaks them down separately for the time of year.
Why? Well, people may not be used to a 90 degree day on April 1, but they probably will be on July 20.
For the urban areas of Philadelphia, Trenton and Wilmington, the following criteria are used:
From May 1 to June 15, heat rates of 96 to 104 degrees are expected.
From June 16 to June 30, heat rates of 98 to 104 degrees are expected.
From July 1 to September 30, heat rates of 100 to 104 degrees are expected.
In the Delmarva and southern New Jersey areas, the threshold is a heat index reading of 105 degrees or higher for at least two hours. Across Philadelphia, the threshold is 100 degrees or more for at least two hours.
Dry heat is different.
The criteria changes again in the desert of the southwest.
As it is very hot for much of the year in the desert, NWS offices in the southwest do not issue heat warnings, only warnings of excessive heat.
The NWS Las Vegas office reports the weather for the highest elevation point and lowest elevation point in the contiguous United States – Mount Whitney and Badwater Basin in Death Valley, respectively, says Jenn Varian, a meteorologist at that office.
“Death Valley regularly exceeds 115 degrees in the summer, but areas like Mount Whitney do not,” Varian said. “So elevation, terrain type in the west, and even the time of year play a big role in how we issue these excessive heat warnings.”
Some offices in the Southwest Southwest also take into account the number of tourists coming to the city and the transitory population that is not used to the extreme heat of the desert.
Safety is the key
It all comes down to the best way to protect the public from various heat-related illnesses, including heat cramps, exhaustion, and stroke. These warnings and advisories serve as a guide to reflect the likelihood of certain heat-related illnesses and even possible deaths from heat exhaustion.
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