The Grey Index
How grey is your winter? We compared sunshine and cloudy days across the cities where grey is a way of life, using official weather service data.
Seattle averages 226 cloudy days a year, more than Buffalo (208) or Pittsburgh (203). In December it gets about a fifth of Phoenix's sunshine.
| City | Latitude | Sunshine hours a year | December sunshine hours |
|---|---|---|---|
| Glasgow | 55.8°N | 1280 | 34 |
| Manchester | 53.4°N | 1411 | 48 |
| Dublin | 53.4°N | 1485 | 57 |
| London | 51.5°N | 1675 | 55 |
| Vancouver | 49.2°N | 1938 | 57 |
| Pittsburgh | 40.5°N | 2021 | 74 |
| Seattle | 47.4°N | 2170 | 53 |
| Buffalo | 42.9°N | 2207 | 69 |
| Portland | 45.6°N | 2341 | 64 |
| Los Angeles | 34.1°N | 3254 | 219 |
| Phoenix | 33.4°N | 3872 | 245 |
When the sun stops making vitamin D
Research from Boston (42°N) found skin made no vitamin D from sunlight from November through February, and at 52°N from October through March (Webb, Kline and Holick, 1988). The NHS advises everyone in the UK to consider vitamin D from October to March (NHS). Every Grey Index city sits between 40°N and 56°N.
Read our guide to vitamin D in Pacific Northwest winters.
Ray™'s take
You cannot change the forecast. You can bring your own weather.
Methodology and sources
Each city uses one official airport or weather station. US sunshine hours are NOAA averages for 1961 to 1990, the latest period NOAA published before its sunshine sensors were retired. Cloudy-day counts are NOAA Comparative Climatic Data averages over each station's period of record. UK figures are Met Office averages for 1991 to 2020, Dublin figures are Met Éireann averages for 1991 to 2020, and Vancouver figures are Environment and Climate Change Canada averages for 1981 to 2010. Countries measure over different periods, so small differences between cities should be read with care.
Sources: NOAA Comparative Climatic Data, Met Office UK climate averages, Met Éireann 1991 to 2020 averages, Environment and Climate Change Canada.