The Year Without Summer by William K. Klingaman, Nicholas P. Klingaman

Geneva was
     lower than in England.
    Their journey by coach from Paris to Geneva took them across the Jura Mountains; Shelley,
     like Mary, did not regret leaving France and the “discontent and sullenness” of Frenchmen.
     The weather in the middle of May was far worse than Mary expected. “The spring, as
     the inhabitants informed us, was unusually late,” she wrote to a friend, “and indeed
     the cold was excessive; as we ascended the mountains the same clouds which rained
     on us in the valleys poured forth large flakes of snow thick and fast.” Initially
     the snow stuck only to the overhanging rocks, but as the coach climbed higher it started
     to freeze on the road.
    Evening fell; the party pressed on, snow pelting against the carriage windows as darkness
     descended. Then Mary could see Lake Geneva and, far in the distance, the Alps. “Never
     was scene more awfully desolate,” she noted. “The trees in these regions are incredibly
     large, and stand in scattered clumps over the white wilderness; the vast expanse of
     snow was chequered only by these gigantic pines, and the poles that marked our road.”
    They settled in a secluded villa known as the Maison Chapuis, a pleasant if humble
     two-story cottage on the south edge of the lake, facing what Mary termed the “dark
     frowning” Jura range. On the infrequent evenings that were pleasant and clear, they
     would sail upon the lake. “Unfortunately,” complained Mary in early June, “an almost
     perpetual rain confines us principally to the house.… The thunderstorms that visit
     us are grander and more terrific than I have ever seen before.” One night a brilliant
     streak of lightning lit up the lake, “the pines on Jura made visible, and all the
     scene illuminated for an instant, when a pitchy blackness succeeded, and the thunder
     came in frightful bursts over our heads amid the darkness.”
    *   *   *
    A S a member of a consortium of New England college professors who regularly made weather
     observations, Professor Chester Dewey of Williams College kept a thermometer suspended
     on the north side of his house, well protected from the sun. Three times a day (7 A.M. , 2 P.M. , and 9 P.M. ), Dewey noted and recorded the temperatures, deducing the mean temperature each day
     from his observations. In the first few days of June, Dewey noticed the temperatures
     fluctuating wildly, as if on a roller coaster. June 1 and 2 were quite warm; the following
     two days were much cooler. June 5 brought sweltering heat: At noon Dewey’s thermometer
     soared to 83 degrees.
    It was not an isolated reading. Montreal reported “hot and sultry” weather on June
     5. To the east, Boston experienced a high of 86 degrees; at Waltham, the mercury reached
     90 degrees; and at Salem, 92 degrees. The Vermont Mirror reported from Middlebury that June 5 was “the warmest day that has here been experienced
     during the season,” and the Rutland Herald noted “the intense summer’s heat.”
    “The mild influence of the sun,” wrote a newspaper editor in eastern Massachusetts,
     “gave us fond anticipations (tho’ our seeds were but just springing out of the ground,)
     of a plentiful harvest.” A wave of thunderstorms passed through in the afternoon,
     cooling the region briefly before unusually high temperatures returned. At ten o’clock
     that evening, Albany recorded a temperature of 72 degrees, 15 degrees warmer than
     the normal overnight low temperature. A reporter in Danville, Vermont, could see heat
     lightning in the distance. “The night was so warm,” noted a resident of Bangor, Maine,
     “that one blanket was sufficient to keep a person comfortable.” Overnight, a steady
     rain developed.
    The warm, humid air and rain in New England preceded a strong low-pressure system
     that was making its way across the Great Lakes on June 5. In the Northern Hemisphere,
     the winds around low-pressure systems spiral counterclockwise; as lows move from