Normally considered a realist, but he also painted many watercolours and some oils in far looser style which I think can be considered to have significant impressionist tendencies. He seldom achieved the high chromas more characteristic of European impressionism, and many of these works were painted quite briskly as studies. However many also bear signatures which imply that they were not solely intended for personal use

See if these examples convince you.

Winslow Homer (1836-1910)

Born in Boston, Massachusetts, in 1836, his mother was a skilled botanical painter in watercolours and his first teacher. He moved to the leafy suburbs of Cambridge at the age of six. He was apprenticed to a commercial lithographer in Boston for two years, but set up as a freelance illustrator in 1857. He supplied illustrations of life in Boston and the countryside around to Harper’s Weekly and other magazines, in a rapidly growing market. In 1859 he moved his studio to New York, where he took classes at the National Academy of Design and learned fine art painting too. He first read Chevreul’s colour theories in 1860.

He was sent to the American Civil War from 1861-5, where he made three trips to the front, sketching military life and battle scenes. His painting Home, Sweet Home (1863) was exhibited at the National Academy and well received, and he spent a year in France in 1867. There he concentrated on landscapes and rural life, and illustrations for Harper’s Weekly showing life in Paris. He was influenced more by the Barbizon School, Breton, Corot, and Millet, than Manet or Courbet. On his return to the US he painted more rural and coastal scenes, and started to show signs in them of his brushwork loosening up.

During the 1870s he stopped work as an illustrator, and concentrated more on watercolours, which became his preferred medium from 1873, when staying in Gloucester, MA, during that summer. At that time, Gloucester was the busiest seaport in the US. Some of these were studies which he then painted in oils, but increasingly he found greater expression in watercolour.

Perhaps as a result of his visit to France, many of his paintings during the 1870s showed very loose brushwork, and greater emphasis on markmaking than previously. At first the critics were disparaging of his watercolours, but they were popular and sold well. He also developed and frequently used a wide range of techniques to enhance his watercolours. These included the use of both transparent and opaque watercolour, thin layered washes, scraping, texture, resist, splattering, and even abrasive paper.

From 1877 he exhibited regularly at the Boston Art Club, where his watercolours achieved recognition. He also met other leading painters of the day, including William Merritt Chase.

In the late 1870s he became more reclusive, living in Gloucester, MA, and at one time in Eastern Point Lighthouse. He spent 1881-2 in the coastal village of Cullercoats, Tyne and Wear, in the north-east of England. There his subjects were the people in the local community and their lives in relationship with the sea, including the local industry of fishing. He painted them almost exclusively in watercolour.

His watercolours from Cullercoats were well received on his return to the US at the end of 1882, with critics welcoming his change of style and vision.

In 1883 he moved to Prouts Neck, Maine, just a stone’s throw from the Atlantic Ocean, where he painted many major works depicting the sea. Unfortunately these did not sell well, but his family supported him. He was able to spend the winters of 1884-5 in Florida, Cuba, and the Bahamas, where he continued his watercolour painting.

He eventually achieved better financial stability in 1900, enabling him to travel more, still painting largely in watercolour. Between 1873 and 1905, he had painted over 700 works in watercolour. He died in 1910.

Winslow Homer never aspired to be an impressionist, but painted many works plein air, with loose brushwork, and conveying impressions. As such, from about 1873 until he went to Cullercoats in 1881, he had an impressionist style, and established himself as America’s foremost watercolour painter.

References

Wikipedia
WikiArt
National Gallery of Art virtual exhibition from 2005.

Tedeschi M and others (2008) Watercolors by Winslow Homer. The Color of Light, Yale UP. ISBN 978 0 300 11945 9. (A unique exploration of his watercolours, examining his techniques and many glorious paintings.)