"dreary day" is a correct and usable expression in written English.
It can be used to describe a day that is dull, cloudy or rainy. For example: "I looked out the window and saw the dreary day outside."
First, on a dreary day, he blithely commented, "Rain is the cloud's pee," then several days later remarked, "Ketchup is my bright light," as he was enjoying his lunch.
It was a dreary day under gloomy skies on a treacherous track.
The agent did not want to ask Rivera to recap a dreary day.
This year the contestants' bright bathing caps and support boats provided splashes of color on an otherwise dreary day.
Got anything better to do with your time on that dreary day than sit on the phone?
PARIS — With the matches turning into mismatches on a clammy, dreary day at the French Open, the consolation was the future.
On a cold and dreary day last winter, I met Roubini over lunch in the TriBeCa neighborhood of New York City.
Fifty years ago, Arnold Palmer flung open his curtains in his room at Rusacks Hotel beside the 18th fairway and looked out on a dreary day of rain.
For example in August 1950 Williams was understudying for Richard Burton in The Seagull: "Dreary day spent watching the lousiest production of 'Seagull' in rehearsal.
For fans, it was just one of nine races on a dreary day at the Queens race track, paying $4.60 on a $2 bet.
When Ramirez punctuated the day with his long home run, Yankee Stadium seemed unusually loud on a dreary day for the home team.
