Data / data

How Summer is changing in the Northeast.

Hotter nights and more rain define the long term trends from DC to Boston.

By Blizzardgeek ·June 26, 2026 ·3 min read

Daily weather records for Boston, New York, Philadelphia and Washington — with New York’s Central Park reaching all the way back to 1869 — tell a remarkably consistent story about how summer in the Northeast has changed. The clearest signals are after dark, and in the rain.

The long view — Central Park, 1869–2025

Records at Central Park go back to the 1860s, providing a clear view of how more warm nights in the summer is the defining long term trend.

Warm summer nights · Central Park 10-yr avg trend

Central Park · hover a year · nights ≥ 70°F per summer

Central Park summer nights at or above 70°F — toggle 75°F — for every year since 1869. The orange line is the 10-year average and the dashed line the long-run trend; most of the rise lands after 1970.

Nights vs. days · Central Park, since 1940

Central Park · anomaly vs 1951–80 · low +0.36°F/decade, high +0.01°F/decade

Mean overnight low versus mean daytime high each summer, as a departure from the 1951–1980 average (5-year smoothed). Since mid-century the low has pulled away from the high — nights are warming, daytime highs much less so.

How has the character of summers changed?

Looking at the distribution of daily high and nightly low temperatures across meteorological summer shows how pronounced the trend is across all four major cities, with comparable records going back to the 1940s. Anyone living in the Northeast instinctively knows that September increasingly feels more like summer and indeed, the long term trends show the near disappearance of cool nights. Notably, DC and Philly do show a trend towards hotter daytime highs that is absent in NYC and Boston.

Daytime highs by decade · NYC

June

July

August

September

1940s

11%

28%

42%

16%

15%

61%

23%

30%

51%

15%

14%

42%

37%

1950s

12%

30%

45%

12%

14%

61%

22%

28%

57%

14%

19%

43%

33%

1960s

30%

47%

15%

17%

58%

22%

21%

65%

12%

19%

41%

32%

1970s

13%

35%

45%

14%

65%

18%

21%

61%

18%

20%

47%

27%

1980s

10%

31%

47%

11%

15%

57%

27%

21%

61%

17%

47%

30%

1990s

30%

49%

12%

16%

55%

26%

20%

62%

16%

19%

49%

28%

2000s

13%

33%

46%

26%

61%

12%

22%

60%

15%

19%

48%

30%

2010s

37%

49%

11%

60%

27%

21%

63%

16%

11%

47%

35%

2020s

41%

12%

68%

26%

24%

61%

16%

56%

26%

100s90s80s70s60s50s40s

Share of each month's daily highs in each 10° band, by decade; use the buttons to switch cities. Hover a segment for its exact share.

Overnight lows by decade · NYC

June

July

August

September

1940s

33%

47%

18%

55%

41%

12%

62%

26%

39%

43%

1950s

37%

49%

13%

57%

40%

65%

29%

38%

43%

11%

1960s

29%

58%

12%

68%

30%

13%

59%

28%

40%

43%

1970s

27%

61%

11%

52%

43%

54%

39%

41%

40%

14%

1980s

26%

59%

14%

50%

47%

43%

40%

44%

11%

1990s

23%

63%

13%

52%

44%

62%

34%

42%

2000s

28%

51%

21%

60%

37%

52%

43%

32%

58%

2010s

22%

58%

20%

36%

60%

51%

47%

32%

51%

17%

2020s

15%

60%

23%

25%

73%

47%

50%

26%

62%

10%

80s70s60s50s40s30s

The same layout, for nightly lows — where the shift is starker: the warm 70s-and-up bands swell through July and August and begin to color June and September.

Are heavy precipitation events more frequent?

With a warming atmosphere that holds more moisture, days of heavy rain are becoming more frequent across all four cities.

Rainy days by intensity · NYC

left: daily inches · right: rainy days / summer

1,703 days shown · frequency trend +0.39 days/decade · daily amount +0.01″/decade

Every summer rainy day (≥0.1″), plotted by amount on the left axis. Filter the intensity ranges and the right-axis frequency line and trend re-fit to just those days; switch cities to compare.

Summer rainfall anomaly · Central Park

Central Park · summer rainfall vs 1951–80 · hover a year

Central Park June–August rainfall as a departure from the 1951–1980 average. The 10-year line drifts slightly wetter, but the larger change is the rising frequency of the heaviest days, above.

Method notes

Daily highs, lows and rainfall come from NOAA’s Global Historical Climatology Network–Daily, in standard units (°F and inches). Stations: NY City Central Park (from 1869), Boston Logan (1936), Philadelphia International (1940) and Washington Reagan National (reliable values from 1942). “Summer” is meteorological summer, June through August, except the distribution grids, which extend through September. Daily mean and anomalies are computed against each station’s 1951–1980 average.

These are raw, unhomogenized observations: they carry the imprint of station moves, instrument and observing-time changes, the growing urban heat island around Central Park and expanding tarmac at the airport sites. That makes the trend within any one station trustworthy, while absolute differences between cities — for instance why Washington’s warm-night count sits so high — partly reflect local siting rather than climate alone.

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