'unexpected weather' is correct and usable in written English.
You can use it to describe a change in the weather that is not normal or expected for a particular time of year. For example: "We had an unexpected cold front move through yesterday, bringing unusually chilly temperatures for mid-July."
Unexpected weather battering a retailer's numbers.
Basic travel insurance typically covers hurricanes or other unexpected weather events.
As tens of thousands people suffered through a flooded and powerless Christmas in Britain, 5,000 miles away unexpected weather was also unleashing havoc on the Caribbean.
Q. Has the summer's unexpected weather -- the lasting heat and droughts in the West, the cool, rainy weather in the Northeast -- been good or bad for business?
Overproduction of food is often tied to unexpected weather patterns and waste is made worse by supermarkets cancelling orders and applying cosmetic standards to produce.
To which I find myself responding: "I worked so hard on setting up that train wreck, introducing surprises on the track, unexpected weather, insufficient trust and unacknowledged emotions.
Alternatively the least weathered samples may actually have some unexpected weathering.
Autonomous Unmanned Aerial Vehicles (UAVs) operate under uncertain environmental conditions and can have to face unexpected obstacles, weather changes and sensor or hardware/software component failures.
"All that unexpected cold weather and rain set back the fabricating of the steel by at least five weeks," said Edmund Florimont, the park's owner.
Decades of allegations about the mob's influence over Italian politics, some real, others imagined, have numbed Italians to the point where newspapers here give more coverage to unexpected bad weather.
With a small crew that included the television journalist Charles Kuralt, Mr. Plaisted made his first attempt to reach the pole in 1967, but the trip had to be aborted far short of the goal, when unexpected warm weather in April caused the ice to begin breaking up.
