Honestly don't know the specifics of how they craft those forecasts, but generally using a probabilistic approach with models/ensembles. I would hazard a guess that some comparison of QPF to flash flood guidance is used to determine areas most prone to potential flash flooding.
They taught my kids how to ID them at school so they don't touch. We were playing golf at Belgrade last weekend and he comes running over telling me he found some, and sure enough there were a bunch under the oak trees by the clubhouse.
Never seen one in my backyard, but bring the kids to school 10 min away in Falmouth and their preschool had a bunch in their oaks. So that trace to moderate from Portland to Falmouth lines up.
My in laws had a huge problem this year at the lake house. They found the cherry trees on the streets and everyone came home from their first visit with rashes all over. They had the trees removed over a week ago but the suckers were still crawling around last week trying to find a place to settle down.
If you are sensitive enough to them and inhale the hairs from a big infestation you can have breathing difficulty. So they warn you not to chuck a fan in the window at night (great news for the AC lovers out there).
There is also a difference between the visible smoke on satellite and the particulate matter that the air quality sensors are measuring. Those particles are pretty small and it may appear clear while still being poor air quality.
Something started taking our seedlings a couple years ago, so I built chicken wire cages to go on top of my beds.
I'm not even entirely convinced they were eating the plants either. It may have been squirrels digging up buried treasure and overturning my veggies.
I believe the cause in Nova Scotia was human activity like @powderfreak described. The official reporting I've seen from Quebec is that most of the fire starts have been lightning (because there aren't any humans in some of these areas).
@Damage In Tolland will be excited to hear that I switched to AC 3 weeks ago. Of course when I'm sleeping during the day on mids and the door is closed my room always sneaks up into the 73/74 degree range because we have so much southern exposure. But I shut all the other heat pumps off and switch mine to cooling.
Yeah, it was a natural feature of my lawn after we built. It honestly wouldn't be my first choice, but it does keep everything green when the south part is baking. My neighbors think it's grass before they actually walk over.