There are many places in the world where clouds are scarce and if you see a lot of them there’s a good chance it’s going to rain. But where I live, there are a lot of clouds all the time. How dark the clouds are (indicating thickness) is a half-decent indicator of whether it might rain. But not really a very good indicator. A lot of the time with dark clouds it doesn’t rain, and it can also rain when the clouds aren’t dark.
What prompted this question is I was a movie and somebody predicted that there was going to be a rainstorm in a minute give or take a few seconds and it happened. It was one of those short but very heavy tropical rainstorms. Is it actually possible to predict it that accurately just by looking at the clouds? Or are there other environmental indicators (they were in a thick forest)?
There are times when it’s possible to predict with pretty high accuracy. I spend a lot of time on the coast. The prevailing winds cause weather to move pretty steadily from west to east. The coast is on a northwest/southeast line, facing northeast. If I see a long line of rain (not just clouds, but clouds with vertical streaks of gray below) in the north, I can be pretty certain it’s coming my way. It might peter out before then, but depending on how socked in it is, I can make a pretty good estimate.
I remember one time on Isle Royal in Lake Superior, on the north side of the island, on a nice sandy beach, sunny & warm. We saw a huge thunderhead to the west, apparently coming right at us. But just before it arrived, it seemed to swerve north and around us. We watched as the rain and lightning fell on the water a few miles out. It continued and then seemed to swerve back southward, to continue its course eastward. Possibly just an illusion of perspective, or possibly the result of higher altitude effects of “shore breeze”. Either way, it was awesome.
When it’s a minute away, around here, anyone can predict it. There are dark clouds overhead, more dark clouds right next to those, the dark clouds right next to the ones overhead have rain visible beneath them, and the wind is blowing hard. That’s easy.
What’s more difficult, and less reliable, is predicting it a few hours in advance.
At certain times of the year we get locked into a daily cycle. (Colorado, Front Range.)
If it’s hot enough, it rains at 2pm, for 30-45 minutes, every day for a month.
Other times, you can see/feel the weather coming hours in advance, snow storms are like that a few times a year.
You can feel it, everybody knows it, but it hovers and waits.
There is also a smell and skin feeling to impending rain or snow. Not sure how to explain it, but it comes with knowing the area you live in. Though snow has a definite smell to it when it is on its way.
I have also felt something on my skin when rain is coming. It feels… Cool but not chilling? Damp? Maybe “soft” is the right word? I’ve often wondered just what physical characteristic I’m picking up on-- I’m guessing it’s either barometric pressure or humidity.
There are some species of plants that will turn their leaves over when rain is pending. For me, I know when a storm is coming because my thumbs hurt like a bitch.
Opposite problem happens when mountaineering sometimes, you can be above the bad weather.
So it’s sunny and warm until you get to the top of the ridgeline or summit, and suddenly there’s a fierce thunderstorm with hail and lightning.
So you run all the way back down the side of a mountain with this giant cold storm pouring down past you out of nowhere.
I think it’s a thing you can train. Certainly there are people who are naturally more (or less) sensitive to it, but I’m guessing most people can do it with practice. I’m not great at it, but I have been able to smell/feel the rain coming sometimes.
Where I live, the arrival of a rain-shower is often closely preceded by squally wind and a sudden drop in temperature. This allows me to predict with reasonable accuracy that it’s about to rain (within a minute or so). The birds notice it too and get all chirpy or fly away.
I’m from Tornado Alley. Some fronts announce themselves with a drop in pressure and temperature, a “rain coming” smell, and wind. Some rains don’t. It depends on the existing conditions. Some clouds say they’re gonna rain, and maybe they do but it all evaporates tens of meters before it hits the ground.
(Around here, it’s actually pretty normal–not common, but not unheard of–to have rain evaporate just after it hits pavement. Effective virga!)