Porto Weather Records (PO000008546)

The annual mean temperature here has risen by 0.1 C (0.1 to 0.2) per decade over 1941 to 2010. In Fahrenheit: 0.2 F (0.1 to 0.3) per decade. The slope is a straight line fitted to 70 complete years; the brackets give its 95 percent interval.

Across 27 years with a frost, the median last spring frost at Porto falls on 14 February and the median first autumn frost on 17 December, which leaves a median of 305 days between them.

Fitted over all years, the growing season changes by -0.2 days per decade at this station.

A day with at least 59.0 mm (2.3 in) of rain is expected about once in 2 years. A day with at least 105.4 mm (4.1 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, 70 years of values from 1941 to 2010.

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: 106.1 mm (4.2 in) in 1986; 101.2 mm (4.0 in) in 1953; 99.0 mm (3.9 in) in 1965.

2 changes were suspected in the annual mean temperature of Porto, at 1989 and 2006. Each is measured against neighbouring stations.

• Relative to 5 neighbouring stations, the station's annual mean temperature from 1989 ran 0.3 C (0.5 F) lower than in the years before (possible change).
• Relative to 5 neighbouring stations, the station's annual mean temperature from 2006 ran 0.3 C (0.6 F) higher than in the years before (possible change).