Pennsylvania College (now Gettysburg College) Prof. Michael Jacobs' weather notes from the Battle of Gettysburg were mentioned in a June 27 Hanover Evening Sun article.
From the Evening Sun:
While future weather cannot be predicted, past weather cannot be disputed.
That is thanks to Dr. Michael Jacobs, a 55-year-old math and science professor at Pennsylvania (now Gettysburg) College about 150 years ago, who began recording local weather data two weeks before the battle.
While spectators might marvel at the heavy wool uniforms worn by re-enactors, Jacobs ' logs reveal the temperature during the actual battle was cooler overall than at most modern re-enactments.
The highest temperature of the three-day battle, 87 degrees, was recorded about the time of the battle 's best known clash, known as Pickett's Charge.
The temperature started as low as 51 degrees at 2 p.m. on June 25 and slowly increased until 2 p.m., July 3. The average temperature for the first three days in July is about 85 degrees, according to the National Weather Service.
After the charging Confederates were driven back to their positions along Seminary Ridge, a strong thunderstorm rolled through the area.
"The thunder seemed tame after the artillery firing of the afternoon," Jacobs wrote in his records, later published as "Notes on the Rebel Invasion of Maryland and Pennsylvania, and the Battle of Gettysburg."
Heavy rains rolled through the area in the days following the battle, turning roads into quagmires and hampering Union efforts to pursue the retreating Confederates. The temperature dropped to the low 70s.
"The low temperature was undoubtedly a great blessing to the wounded, as well as to all in both armies, in protecting them, in their forced marches, from dangers as fatal as bullets," wrote Jacobs. "The frequent rains cleansed the fields of much that would have caused disease."