Firefighters were concerned Sunday about the possibility of fire spreading under trees and a warming forecast later in the week.

By Friday morning, Seattle will have a 90% chance of rain, the weather service said, and the probability of rainfall rises to 100% by Friday night. The Seattle area could see up to 1.25 inches of rain on Friday alone, according to the forecast. Chances of rain drop to 70% on Saturday, when less than a 10th of an inch of rain is expected to fall.

The process of creating a pyrocumulus cloud (pyro- meaning “fire) is almost identical to how an actual thunderstorm is produced, by rising warm air currents into a colder environment aloft. And sometimes,