Weather Patterns, April 17-20, 1775
The weather on the day of the battle has been described by historians in contradictory ways. Hudson writes, “All accounts agree that the day was unusually warm for that season of the year” (Lexington, 197). Murdock disagrees. “Contrary to general belief,” he writes, “the 19th of April seems to have been a cold, windy day, with a bright sun … evidently the wind was east” (The Nineteenth of April, 1775, 55). Both of these statements are incorrect.
The New England weather was typically volatile in this period. The 18th of April was wet through the day, followed by rapid clearing at night. Winds were variable, veering from the northeast to the south. The following diary entries were recorded for this day:“rain” by Nathaniel Ames, Dedham; a “fine rain” by Jonas Clarke in Lexington; “rainy most of the day” by Joseph Andrews; “rain a.m. fair towards night by Ebenezer Gay of Suffield, Conn. An anonymous Concord weather diary records “rain” in the morning and “showers” in the afternoon, with a south wind. Jeremy Belknap in Dover, N.H., described the 17th of April as “fair” and “warm,” with small showers in the afternoon and rain with a northeasterly wind at night, and the 18th as “warm rain pm cloudy.”
In the evening and night of April 18 (when the British expedition set off for Concord, and Paul Revere made his midnight ride) clearing followed rapidly. Revere remembered in his letter to Jeremy Belknap that the night was “very pleasant.” Sanderson described it as “a pleasant evening” (Phinney, Lexington 23).
For the 19th of April, the primary evidence of twelve diaries is highly consistent. In Cambridge, Harvard professor John Winthrop took two readings of his thermometer that day. At six o’clock in the morning, he noted that the temperature was 46 degrees, the barometer 29.56 inches and rising, the sky fair, and light winds from the west. At one o’clock in the afternoon, the temperature had risen to 52 degrees, the sky was fair with clouds, and the west wind had freshened. At that point he noted, “battle of Concord will put a stop to observing.” He and his wife Hannah fled for their lives.
Other diarists described the weather that day in the same way. Lexington’s minister Jonas Clarke found a moment to note that the day was “clear.” In Boston, Dr. John Jeffries wrote, “clear and fair, fresh wind at W.” The Rev. William Marrett in Burlington thought the day was “fair, windy and cold.” Paul Litchfield of Scituate described it as “somewhat blustery and cool.” Elizabeth Stiles in Newport, R. L., recorded a temperature of 53 degrees at 11 am, fair skies and the wind from west. Jeremy Belknap, in Dover, N. H., called it “fair, windy, cool, w[est wind].” Ebenezer Gay, in Suffield, Conn., thought the day was “fair, cold.” Dr. Nathaniel Ames, in Dedham described it as “clear.” William Clark in the same town described the day as “fair” with a “strong chilly west wind.” An anonymous weather diary, now in the Concord Free Public Library, described the 19th as “fair with a westerly wind.”
The best secondary account is David Ludlum, “The Weather of Independence,” in The Country Journal New England Weather Book (Boston, 1976), 126-28. Ludlum, editor of the American Meteorological Society’s journal Weatherwise, concludes that “these records indicate that a cold front passed through eastern Massachusetts about noon on April 18, bringing an end to the showery conditions, a shift of wind to the west, a rising barometer, and a rather rapid postfrontal clearing. Visibility was good late in the evening when the signal lamps were hung.” This is by far the most accurate judgment, but requires amendment in one detail. Some diaries reported showers persisting into the late afternoon of the 18th. After two days of rain, the ground, normally wet in mid-April, was very soft—as one of Paul Revere’s pursuers discovered by experience. The streams were high, as Smith’s British infantry learned the hard way. By all accounts, the day of the battle was crisp, cool, and fair, with a rising westerly wind and fluffy cumulus clouds scudding across bright blue skies.
Late in the day, another storm system moved rapidly through the area, with a red sunset, and later a cold rain that made a miserable night for both the American militia who were “lying on their arms” at Cambridge, and the British Regulars who were sleeping in the open on Bunker Hill.
SOURCES: The Nathaniel Ames Diary and William Clark Diary, Dedham Historical Society; an anonymous weather diary, CFPL; the Winthrop weather diary, Harvard Archives; Jonas Clarke Diary, MHS; diaries of Jeremy Belknap, Ebenezer Gay, Joseph Andrews, and Paul Litchfield, all in MHS. The Marrett Diary is quoted in Frothingham, Siege of Boston, 59, 84n; the Stiles Diary and Jeffries Diary, in Ludlum, The Country Journal New England Weather Book, 127.