Chatham Weather Records (CA008100990)

The fitted trend in annual mean temperature here over 1873 to 1946 is 0.06 C (-0.02 to 0.15) per decade. The interval includes zero, so the trend is not clearly different from zero. In Fahrenheit: 0.12 F (-0.03 to 0.26) per decade. The slope is a straight line fitted to 73 complete years; the brackets give its 95 percent interval.

Across 73 years with a frost, the median last spring frost at Chatham falls on 19 May and the median first autumn frost on 27 September, which leaves a median of 132 days between them.

In 1916 to 1946 the median growing season was 126 days. That is 8 days fewer than in 1873 to 1902.

Fitted over all years, the growing season changes by -1.4 days per decade at this station.

A day with at least 49.2 mm (1.9 in) of rain is expected about once in 2 years. A day with at least 97.6 mm (3.8 in) of rain is expected about once in 100 years.

The levels come from a generalised extreme value (GEV) distribution fitted by L-moments to the wettest-day total of each year, 74 years of values from 1873 to 1946.

A return level is an estimate. It is least reliable for the long periods, 50 and 100 years, and for any period longer than the record behind the fit, where the fit has to reach past the largest day actually observed. It is not a forecast.

The largest wettest-day totals in the fit: 85.9 mm (3.4 in) in 1879; 85.9 mm (3.4 in) in 1933; 84.6 mm (3.3 in) in 1909.

3 changes were suspected in the annual mean temperature of Chatham, at 1899, 1904 and 1923. Each is measured against neighbouring stations.

• Relative to 5 neighbouring stations, the station's annual mean temperature from 1899 ran 0.4 C (0.7 F) lower than in the years before (likely change).
• Relative to 5 neighbouring stations, the station's annual mean temperature from 1904 ran 0.6 C (1.2 F) higher than in the years before (likely change).
• Relative to 5 neighbouring stations, the station's annual mean temperature from 1923 ran 0.5 C (1.0 F) lower than in the years before (likely change).