unseasonable weather is not the type of weather that you expect in a particular season
Origin and usage
The adjective unseasonable is formed from the adjective ‘seasonable’ and the prefix ‘un-‘. It was first used in the 16th century.
As the British Isles were swept by gales and heavy rain for the second week in a row, people spoke of unseasonable weather, which is any kind of weather that is not typical of the season in which it occurs, but especially bad weather when you expect good. Frequent collocates of unseasonable, along with ‘weather’, are warmth and cold, as well as more specific terms such as heatwave, blizzard, snowstorm, frost and chill. Adjectives that often occur alongside unseasonable include unpredictable, crazy and extreme, reinforcing the idea that things are not as they should be. The related adverb is unseasonably and typical collocates include warm, hot, mild, balmy, cold, chilly and frigid, as well as wet and dry. The base adjective seasonable means suitable or normal for a particular time of year. It is sometimes used as a synonym for ‘seasonal’, a use that some find objectionable.
“It is still unseasonably warm here right now, melting a lot of our early snow.”
“… the unseasonable seasons drove, With alternating shafts of frost and fire
(Shelley, Prometheus Unbound)
“The true wisdom is to be always seasonable, and to change with a good grace in changing circumstances.”
(Robert Louis Stevenson)
foul, harsh, inclement, severe