Some Hazards of Weather When Painting Outdoors
Other arguments against painting outdoors involve the hazards of unpredictable weather.
1.Rain. Just a light shower may ruin a watercolour but oil paintings are vulnerable too. Although works in oil on canvas are extremely durable, as evidenced by the 500-year-old paintings in art museums around the world, moisture on a canvas in progress can lead to a condition called 'bloom.' This results in a whitish appearance across the work, similar to the 'bloom' on the skin of a grape.
2.Wind. A light breeze will shake a canvas on stretchers, causing a 'bounce' that makes precision work harder for the artist. Painting on a rigid panel such as MDF board overcomes this problem but raises a worse one for the future of the painting created on its acidic surface. The watercolour artist isn't bothered by ruffling of his paper but if the sheet was soaked and stretched in the proper way, drying-out is a worry.
3.Glare. The intense light from the sky on a sunny day can cause the artist to make errors in judging the colour mixtures she is making on the palette.
My most compelling objection is the last: your paintings are never likely to be seen in daylight.