Dr Jacobs' weather observations, June 25th through July 4th 1863

I've often wondered how the weather influenced various battles during the CW. It had to have an impact, as the article you posted indicates.

"It is, however, for military men to determine what effect the atmospheric conditions had upon the conflict, and to conjecture what result might have followed had we had that year an average July, not to say one of such extreme heat as that through which we have just passed".

I hope there are more contributions to this thread as it's an interesting topic from my perspective. Thanks for sharing.
 
For those unfamiliar with Pennsylvania summers, the humidity can be draining. I've been on 21st century exercises where it can be 115 degrees Fahrenheit in the sun at noon on a July day, and any exertion leaves successive high-tide salt stains on one's uniform.

Now imagine that 1) a poor diet with 2) limited water after 3) a long march in 4) a wool uniform with a 10lb weapon plus gear, while facing the stress of 5) an impending battle.

It was 87 degrees at 2pm on the afternoon of July 3rd, 1863, when Pickett started his men moving.
 
Pretty mild temps for July and lots of cloud cover I would have to think the temps weren't a factor although with the on and off rain I bet the humidity was high. There was a very interesting episode of Battlefield Detectives on the History Channel about the Rev. War battle of Monmouth NJ. where the extreme heat was a big factor in the battle. They had two current military men dress in British and Colonial uniforms and do exercises and run on a treadmill in similar heat and had doctors monitoring the effects of the heat and heavy uniforms. They also found chewed musket balls that they would chew to try to produce spit to quench their thirst. Guess there was no worry of lead poisoning in those days. Anyway it was a very interesting episode that dealt with the weather I'm sure could be found online if interested.
 
A lot of people assume that it was unusually hot during the battle because of the reports from the soldiers. However, as you can see, the temperatures were in the normal range for Gettysburg during that time of year. It also appears that they were below average on July 1 and 2. Also, we don't know the humidity. It's not always humid if the temperatures are in the 70s in the afternoon. However, as others have said, if you take into account the wool uniforms and gear, it would feel extremely oppressive.
 
From his vantage point, Professor Michael Jacobs missed a few weather events in the area, based on soldier accounts.

July 1: A light drizzle occurred near Marsh Creek around 6 a.m., and also near Uniontown, Maryland. There was a heavy shower on South Mountain at mid-morning. Humidity was very high; consequently soldiers fell out from the Union First, Third and Twelfth Corps. There was a slight westerly breeze at Gettysburg later in the day. In the late afternoon, a heavy shower passed a half mile east of town.

July 2: Early morning showers were recorded about three miles southeast of Gettysburg. A ground fog appeared in spots near Gettysburg owing to the high humidity and dead calm, which had dissipated by mid-morning.

July 3: Patchy fog and smoke from campfires obstructed the view from Little Round Top at 8:15 a.m., but the sky was bright by 11 a.m. The heat was oppressive in the afternoon, and many who were lying in the sun (like most of Pickett's men) endured temperatures up to 15 degrees higher than the 87 degrees in the shade reported by Jacobs. By 9:20 p.m. a bright moon was up in the eastern sky (the moon was full two days previous).

July 4: The sun broke briefly on the horizon (sunrise at 4:36 a.m.) before becoming enveloped by a foreboding overcast sky.
 
temperatures up to 15 degrees higher than the 87 degrees in the shade reported by Jacobs. .

Not that I doubt you, but what's the source for 1) Jacobs taking his readings in the shade and 2) 15 degrees higher?
 
Interesting thread. I have never spent much time in researching weathers impact on CW battles. Just a short list of weather related questions that came to mind.

1) Was weather forecasting based on a simple report on nearby towns weather? I.E., if it was raining in Pittsburgh, did someone telegraph that so people east of Pittsburgh knew rain was coming? Maybe it was simple as looking at the clouds.

2) How hard of a rain would be necessary before battle operations would have to cease due to the fear of wet gun powder?

3) How much of a factor was wind in aiming small arms or artillery shells?

4) Did humidity affect shell fuse burn times?

I can't imagine the amount of water needed to supply 150,000 men, thousands of horses and mules fighting during the summer in wool uniforms.
 
1) Was weather forecasting based on a simple report on nearby towns weather? I.E., if it was raining in Pittsburgh, did someone telegraph that so people east of Pittsburgh knew rain was coming? Maybe it was simple as looking at the clouds.

Good question for both Federal and Confederate specifics. In general, weather patterns had been known since Benjamin Franklin was printing the Farmers' Almanac.

From 1861 to 1865, Joseph Henry's meteorological program was severely disrupted by the Civil War. Weather data took a back seat to other important business requiring telegraph lines, and secession prevented southern observers from using the postal service7 to mail their registers. Many observers joined the war effort.8 Others wrote to say their weather instruments had been confiscated or destroyed.9 The strained finances of the Smithsonian, which depended in part on annual Congressional appropriations, made it unable to comply with observer requests10 for barometers, rain gauges, or other such items.
https://siarchives.si.edu/history/exhibits/henry/meteorology

The prevailing winds push north and east, so looking south and west at what's happening in WV is a better barometer than Pittsburgh.
See current day https://radar.weather.gov/radar.php?rid=lwx&product=N0R&overlay=11101111&loop=no
 
Not that I doubt you, but what's the source for 1) Jacobs taking his readings in the shade and 2) 15 degrees higher?

A lot of people don't realize that those who keep temperature records almost always take readings in the shade. That's so that you are measuring the actual temperature of the air and not the temperature of materials affected by the absorption of the direct rays of the sun. It's really not valid to measure temperature in the sun because 1) the thermometer would be adding the heat from its own absorption of sunlight and 2) the absorbed heat of the surfaces that are near the thermometer. That's why, even today, official thermometers are placed in the shade, high off the ground, so that the heat from the ground does not affect the reading.
 
A lot of people don't realize that those who keep temperature records almost always take readings in the shade. .

Gotcha, having suffered through Pennsylvania summers in direct sunlight & the rest would make sense. Still, do you have a link for mid-19th century standards on that?

Jacobs had been maintaining a Meteorological Station at Gettysburg since 1849 & was corresponding with the Smithsonian Institute, so presumably he'd have been adhering to period standards.
See p.81 http://www.biodiversitylibrary.org/page/7798652#page/89/mode/1up
 
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A lot of people don't realize that those who keep temperature records almost always take readings in the shade. That's so that you are measuring the actual temperature of the air and not the temperature of materials affected by the absorption of the direct rays of the sun. It's really not valid to measure temperature in the sun because 1) the thermometer would be adding the heat from its own absorption of sunlight and 2) the absorbed heat of the surfaces that are near the thermometer. That's why, even today, official thermometers are placed in the shade, high off the ground, so that the heat from the ground does not affect the reading.
That's really interesting...I had no idea! Makes sense though.
 
Interesting thread. I have never spent much time in researching weathers impact on CW battles.

That's why the first thing briefed in a 20th/21st century Operations Order is the weather, by the Intelligence Officer (who starts the briefing).
 
3) How much of a factor was wind in aiming small arms or artillery shells?

That's compensated for by calculating windage (speed and direction of wind versus direction of aim, powder charge, distance and type of projectile). There were myriad charts for artillery pieces and if one is familiar enough with a rifle, 'Kentucky Windage' applies.

See also https://civilwartalk.com/threads/cannon-fire-and-rain.9780/

Our high school physics professor use to give problems like this -
TUB8CPx.gif
 
2) How hard of a rain would be necessary before battle operations would have to cease due to the fear of wet gun powder?
"That depends" http://www.weatherbook.com/early.html

It was now three o'clock in the afternoon, and raining. For fifteen hours we had been wet to the skin. Chilled, sleepy, hungry and disappointed--profoundly disgusted with the inglorious part to which they had been condemned--the men of my regiment did everything doggedly. The spirit had gone quite out of them. Blue sheets of powder smoke, drifting amongst the trees, settling against the hillsides and beaten into nothingness by the falling rain, filled the air with their peculiar pungent odor, but it no longer stimulated. For miles on either hand could be heard the hoarse murmur of the battle, breaking out nearby with frightful distinctness, or sinking to a murmur in the distance; and the one sound aroused no more attention than the other.

- 'What I Saw of Shiloh', Ambrose Bierce
http://www.online-literature.com/bierce/2037/
 
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Gotcha, having suffered through Pennsylvania summers in direct sunlight & the rest would make sense. Still, do you have a link for mid-19th century standards on that?

Great question. I don't have a link, but I base my reasoning on this: People have been measuring temperatures for centuries. Anyone who is scientifically inclined and taking regular temperature readings would have eventually realized that temperatures taken in the shade are pretty consistent, whether your thermometer is in the front yard or back yard. Otherwise, your readings would vary wildly, depending on whether you placed your thermometer in partial sunshine or total sunshine. Also, the observer would have noticed that on a day that the sun peaks in and out of the clouds, an exposed thermometer would suddenly jump each time the sun would shine on it and then go back down when a cloud brought shade.
 
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