During the days before a major thunderstorm hits, emergency room visits for seniors who suffer from asthma and chronic obstructive pulmonary disease (COPD) rose significantly, according to a research letter published Monday in JAMA Internal Medicine.

Although the study used Medicare data for those 65 years and older, the danger is just as real for younger people with severe respiratory illnesses, said study author Dr.

All levels, however, did drop after the storms ended.

"Prior studies suggest that rapid temperature increases can precipitate respiratory problems, and we observed changes in temperature in the days prior to thunderstorms," he added.

"The last thing to note is that this was a study of thousands of thunderstorms occurring across the US, matched to high-frequency data on environmental parameters and hospitalizations, which makes these findings potentially more generalizable than previous studies on this topic," Jena said.

Day before storm is more dangerous

The study analyzed Medicare insurance claims for emergency room visits tied to acute respiratory distress between January 1999 and December 2012, comparing the data to atmospheric and lightning data from the US National Oceanic and Atmospheric Administration for every US county.

"We found ER visits rose in the days leading up to the thunderstorm when temperature is rising and the amount of particulate matter in the air begins to rise," said Jena.

Particulate matter is a mixture of solid and liquid matter found in the air.

Using those numbers, the study estimated an additional 52,000 emergency room visits over the 14-year period due to respiratory distress in the three or more days surrounding major storms.

"If you know a thunderstorm is coming, be mindful just as you would when pollen counts are high, and take a little extra care," Jena advised.