Climate Normals

A climatological summary of the historical meteorological series of the Palermo Astronomical Observatory, including 30-year normals, temperatures, precipitation and typical-year charts.

Technical report: F. Bocchino & F. Damiani, INAF-OAPa, September 2025

Introduction

This section presents the climate normals of the historical meteorological series of the Palermo Astronomical Observatory "G.S. Vaiana", at the Palazzo Reale site. Values are computed according to World Meteorological Organization (WMO) standards over consecutive 30-year periods, from the 1871–1900 period to the current reference 1991–2020.

The historical series spans more than 150 years of observations and is one of the longest urban meteorological records in Italy.

Methodology

Climate normals are averages of meteorological variables computed over 30 consecutive years. WMO validity criteria are applied to each parameter: a month is included only if it has sufficiently complete data (for temperatures: at most 5 missing days total and no more than 3 consecutive; for precipitation: complete monthly series). A monthly normal is calculated only if at least 80% of the years in the period are available (24 out of 30).

Parameters calculated: minimum temperature (Tmin), mean temperature (Tavg = (Tmin+Tmax)/2), maximum temperature (Tmax), total precipitation (mm), rainy days (precipitation > 1 mm/day), heavy rain days (> 10 mm/day), mean rain intensity (mm per rainy day).

Methodology in accordance with: WMO, "Calculation of Monthly and Annual 30-Year Standard Normals", WCDP-10, 1989.

Monthly normals

The following charts show the evolution of monthly normals across the 14 available 30-year periods (1871–2030), with statistical distributions of annual values within each period.

Monthly minimum temperature

Open image Download CSV

Monthly mean temperature

Open image Download CSV

Monthly maximum temperature

Open image Download CSV

Monthly precipitation

Open image Download CSV

Monthly rainy days

Open image Download CSV

Heavy rain days (>10 mm)

Open image Download CSV

Monthly rain intensity

Open image Download CSV

Annual normals

The annual chart summarises all parameters for each 30-year period.

Annual normals summary by period

Period	Tmin (°C)	Tavg (°C)	Tmax (°C)	Rain (mm)	Rainy days	Days >10 mm	Intensity (mm/day)
1871-1900	14,4	17,8	21,2	582,3	78,3	16,9	6,47
1881-1910	13,9	—	21,0	574,5	79,6	16,6	6,52
1891-1920	13,7	17,2	20,7	561,8	74,9	16,6	6,61
1901-1930	—	—	—	520,2	68,0	15,9	6,66
1911-1940	14,4	17,7	21,0	539,8	64,7	15,6	6,93
1921-1950	14,5	18,1	21,7	526,2	65,0	15,2	6,86
1931-1960	14,4	18,3	22,2	525,1	66,6	14,1	6,65
1941-1970	14,2	18,3	22,3	474,5	65,0	12,8	6,31
1951-1980	13,8	18,0	22,2	460,2	65,3	12,2	6,12
1961-1990	14,0	18,0	22,1	451,2	64,7	12,1	6,14
1971-2000	14,4	18,2	22,0	491,1	64,9	13,4	6,76
1981-2010	15,4	18,7	22,1	551,8	68,0	15,4	7,06
1991-2020	15,8	19,1	22,4	614,6	71,8	17,8	7,70
2001-2030	—	—	—	—	—	—	—

Download CSV — Full annual normals (all parameters)

Temperature

Temperatures are represented as the average of daily minimum, mean and maximum temperature for each month and 30-year period.

Monthly minimum temperature

Open image Download CSV

Monthly mean temperature

Open image Download CSV

Monthly maximum temperature

Open image Download CSV

Precipitation

Precipitation includes the monthly total (mm), days with rainfall above 1 mm, heavy rain days (> 10 mm) and the mean rain intensity in mm per rainy day.

Monthly precipitation

Open image Download CSV

Monthly rainy days

Open image Download CSV

Heavy rain days (>10 mm)

Open image Download CSV

Monthly rain intensity

Open image Download CSV

Typical year

The typical year summarizes the average daily behaviour of temperature and precipitation across the annual cycle.

Typical year 1871–present: daily evolution of minimum and maximum temperature and precipitation. — Typical year data 1871–present (CSV)

Typical year for the 1991–2020 reference period. — Typical year data 1991–2020 (CSV)

Data download

All climatological data are available for download in CSV format.

Full annual normals (all parameters) Download

Minimum temperature — monthly normals by period Download

Mean temperature — monthly normals by period Download

Maximum temperature — monthly normals by period Download

Precipitation — monthly normals by period Download

Rainy days — monthly normals by period Download

Heavy rain days — monthly normals by period Download

Rain intensity — monthly normals by period Download

Typical year (daily) 1871–present Download

Typical year (daily) 1991–2020 Download

Technical notes

The data and charts published in this section derive from climatological products already processed and documented in the technical report.
Station coordinates: 38.1115° N, 13.3532° E — Elevation: 75 m — Site: Palazzo Reale, Palermo
WMO Region: VI — Europe. WMO Block/Index: not yet assigned.
Full technical report (PDF)