Modern meteorology saves lives. During summer months in humid climates, meteorologists fill our screens with forecasts for high temperatures, rising dew points, and extreme heat indices. Corresponding heat advisories from the National Weather Service warn of the life-threatening circumstances for those who fail to exercise discretion in their outdoor activities. To ensure our safety, we are cautioned to slow down, hydrate, and stay indoors. But for those who fought in the Civil War, there were no such warnings, nor were such discretions allowed to be the better part of valor. The recent discovery of certain primary-source weather data, however, allows us to reach back in time and project modern science on the human experience of those who fought in the war.
As a licensed battlefield guide at Gettysburg, one of the most frequent questions I am asked by visitors is, “How hot did it feel to the soldiers during Pickett’s Charge?” For most, this is an idle curiosity. But for historians, the question has always been, “were the actual weather conditions severe enough to play a role in the outcome of the charge?” Unfortunately, though we knew what the temperature was an hour before the charge on July 3, 1863, we did not know what the measure of atmospheric moisture was, so we could never say with certainty what the weather felt like. And without that key data, we could never engage in a meaningful conversation about the weather’s potential impact on the climactic attack.
Weather observation data faithfully recorded during the battle by Gettysburg College’s Professor Michael Jacobs, who was doing so on behalf of the Smithsonian Institution, indicated a high temperature of 87°F an hour before the charge. Historians, however, have long assumed that it must have felt much hotter. And with good reason, for in the mid-Atlantic region oppressive
