Heat Waves

Why is it that the heat waves seem to have a greater affect on the people on the East coast or in the Midwest than here in Utah? If I am using the Heat Index tables correctly, then New York should experience a heat index of 120-130 in the next few days. The tables don't get down to lower humidity, but St George could easily reach a heat index on 130 on a really hot day, say 109 degrees. And Phoenix or Las Vegas should reach that high for even more days throughout the year. But you rarely hear about how bad the heat is in Phoenix, Nevada, or Utah. Why not? Does it really feel hotter in the east?

John T.

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John's question is a great point, why do we hear so much about heat waves in Chicago or Boston, it gets to 100 here every summer. Are the people there just in worse shape to handle the heat?

A few answers to this question. Cities like Boston or anywhere in New England and even a place like Chicago, these places aren't that warm every summer, so many residents and buildings don't have A/C. Boston, a very old city, has very old homes, not a lot of A/C going on there, and it's not cost effective in some of those towns nearby either. Being from New England, my parents often don't even put the A/C unit in their bedroom in the summers because it's just not worth the trouble for the rare usage. Some people still have cars without A/C since you don't need it that often. They only really need to use the air a few times a year in the homes so why would you buy one then? That's part of the problem.

When we talk heat index, we are looking at how hot it actually feels when you combine the humidity with the temperature. In the west, our climate is not nearly as humid as the east coast. It's that absence of humidity that makes dealing with 100 degree heat much more bearable. When temperatures reach 100 on the east coast, you can beat it's going to be humid and uncomfortable.

Using a heat index chart, let's look at the observation from Boston earlier this week. On August 2nd, at 3 pm, Boston hit 98 degrees, the dewpoint was 73!! The Relative Humidity is 45%. Using the heat index chart, it felt like 104 in Boston! Boston's normal high temperature is around 82, so 104 is crazy for the people there.

Unlike us, they don't experience 100 degree heat regularly, and the lack of A/C is a big deal, there's not as many places for people to go who might be sensitive to the heat. People who are not used to the heat can be unprepared as well, they aren't used to having to drink so much water or take it easy, this is part of the reason for so many unfortunate injuries or fatalities.

For St. George or Pheonix to hit a 45% humidity is pretty incredible. Unless it's raining, usually our humidity isn't that high. On July 16th in St. George, the high temperature was 111 degrees, but the RH was 10%! That on the heat index chart actually makes it feel like 105 degrees outside.

Average humidity levels in St. George is around 9% during the summer months. This low humidity means that sweat can evaporate readily, and that cools us off. When humidity gets really high up, we have clouds and rain and it's usually not as hot.

In Phoenix, on the 21st of July it reached a scorching 118 degrees. However at that hour, the RH was around 10% so the heat index was not a big issue. When the humidity begain to rise and thunderstorms were near, the air temperature actually dropped a bit.

Does it feel hotter in the east? Well, we just saw the two different days in St. George and Boston, both days "felt" like 104 or 105 degrees. Yes, it feels hotter because of the higher humidity. When the humidity is higher, it's harder to cool off your body because your sweat doesn't evaporate as fast. So that would make a person feel hotter. 105 here in Utah is feels a lot different than 105 with high humidity elsewhere.

Answered by KSL Meteorologist Dina Freedman.