[Physics] Rain system movements and highways

Question

In my free time I sometimes enjoy watching the weather or radar and trying to predict how a rain system will move. Pretty often I notice that a small rain system or even a large one will congregate or follow a large interstate highway. I wonder if this is just a coincidence or has physical validity. Possibly it has something to do with heat convection from the road as it will usually be hotter than the surrounding ground? Anyways seeing if anyone could pose some viable physical reasoning or explanation or refutation.

Answer 1

Pretty often I notice that a small rain system or even a large one will congregate or follow a large interstate highway

It is like urban pollution. A storm releases rain over cities:

City pollution may also impact cloud formation and rainfall. “Water vapor doesn’t ordinarily spontaneously condense into drops to form clouds,” says climate scientist Tom Bell, from NASA Goddard Space Flight Center. “It needs dirt to form around. All rain needs aerosols to form.” In the natural world, cloud-forming aerosols are things like sea salt, dust, and pollen, all of which are large particles. But pollution aerosols are usually smaller and more numerous than natural aerosols. With lots of particles to collect on, water coalesces into many tiny droplets instead of larger rain-sized drops. The impact on rain, says Bell, varies depending on where the clouds form. In some cases, urban aerosols suppress rain, but in others they increase it.

So it must be that given a saturated system passing over land, where large highways with lots of polluting cars are, a corresponding pollution corridor will be over the highway. The combination of the higher heat from the concrete/asphalt and the heat exhausts of cars could tip the point towards precipitation in this scenario:

What causes the difference? Scientists are still working on that question, but Bell and others believe that the temperature difference between the air near the ground and the atmosphere above may be one key difference. “Bubbles of hot air form over land and rise like a bubble in a pot of boiling water,” says Bell. The rising air cools, and many tiny droplets form around urban aerosols. These small drops are not large enough to fall, so the storm tends not to produce rain.

More rain can occur when the bubble of heated air forms over a very warm area, however. “The bubble of heated air rises faster and climbs higher in the atmosphere,” says Bell. Because of urban pollution, “droplets that would normally fall out at a lower elevation are smaller and go higher.” Now high in the atmosphere, the tiny water droplets turn to ice. To make the transition from liquid to solid, the water molecules have to release heat. “The added heat kicks in an ‘afterburner,’ and the bubble of air is pushed up higher and faster,” Bell explains.

“The extra boost makes the storm act like a vacuum cleaner,” says Bell. “Something needs to replace the rising air, so more moist air is sucked up.” This vacuum-cleaner effect allows the storm to pull in more material to work with than it would have without the urban aerosols, and more rain results. “The effect only happens when fast-rising air would form a thunderstorm anyway, and when the air near the surface is moist,” Bell adds.

Chances are, the urban heat island, city structures, and pollution all interact to alter rain storms around cities. “The real question is which combination of those is the most important factor,” says Shepherd. “Which of those takes the most precedence at the beginning? Is there one of those that takes more precedence at the end, once rainfall gets started? That’s what we’re trying to study right now.”

Actually if this observation of yours is verified statistically it might help the modelers on deciding on a model for rain from pollution. It is like a contained experiment.