At least in the northeast, we often experience storms that move along certain highways. For example, the New Jersey Turnpike is often shown as the dividing line of where it might snow vs. where it may rain.
Similarly, there is often distinct differences in weather one one side of the Hudson vs. the other. Sometimes I can be in midtown Manhattan and see that the weather is completely different in the Bronx.
I acknowledge there may be some “chicken-egg” answers to these questions, which is why I put it in IMHO.
I’ve noticed the same thing in my state. US Interstate 90 roughly cuts Montana into north and south, at least on the western side, and weather is often very different just a few miles north or south of Hwy 90. I always assumed it was a coincidence and had nothing to do with the highway, but now I’m not so sure.
I live within walking distance of the Columbia River, and I have noticed that clouds coming from the north tend to go west a bit once they get near the river.
In Lorain County, Ohio there are numerous roads named as “ridge” roads. North Ridge, Middle Ridge, Center Ridge, West Ridge, Murray Ridge, Sugar Ridge etc.The east-west ridge roads are shorelines of various iterations of Lake Erie over the ages. Each one is really a ridge that slopes sharply down to the north. I can’t tell you how many times I have seen rain on one side of the ridge and not the other. I guess the surface air is being deflected upwards enough to influence rainfall in some cases.
Another observation point. For many years I lived on the south shore of Long Island, NY on a barrier island. My view was of the main island. Many times I have seen things like heavy rain on the main island that didn’t come across the bay/channel, though I have seen it come across the channel as well, sometimes in very dramatic fashion. It could appear that the water somehow acted like some sort of barrier. It was also great to be outside, sometimes in the sun looking at the heavy rain across it. It didn’t seem to work the other way, or at least not often enough to be noticeable. This also applied to snow fall totals, we rarely got as much snow as the main island, though I think that one was more of the ocean and bay warming the land as well as the breeze being warmed by the ocean/bay during winter, and perhaps even the salt air coating the ground causing an additional snowmelt.
The roads are where they are for a reason; and some of the reason is generally historical – which means that the roads follow the line of geological features that suited old travel methods, and those may affect the weather.
Around here it’s Routes 5&20. These follow, fairly closely, an ancient Native trail that runs along a line across the north end of the larger Finger Lakes. And yes the weather’s different when you’re actually in the area between the Finger Lakes than when you’re going along between them and the Lake Ontario – but that’s not because of the road, the weather patterns were there long before the road. The road is there because the land’s relatively level and also because ground travel can’t get across the Finger Lakes and that’s the furthest point south that allows travelling directly east or west along the line just north of them.
Interstate 95 through eastern New England (Rhode Island and Massachusetts, New Hampshire, and southern Maine) is often the rain/snow line or the line where coastal storm impacts drop off sharply. It’s also the line where the coastal plain generally ends and the elevation starts to rise as you move inland.
Interstate 90 (the Mass Pike) is also often another rain/snow line. I’d like to say that one is also likely elevation related, but there is roughly equal terrain/elevation on both sides of the pike. Maybe the storms don’t want to pay the toll.
I have always lived within a few miles of the Mississippi River, either on the Missouri side or the Illinois side. This may simply be confirmation bias or coincidence, but tornados coming from the west seem to hop when they cross the river, rarely doing much damage within a few miles of the eastern bank.
I’m quite confident that roads are too small to effect weather, and would wager the same holds true for rivers. Around Chicago, they often talk about weather differing north and south of I80, and east or west of I 65 in Indiana. But those roads just delineate the lake effect of Lake Michigan, depending on whether the wind is westerly or northerly.
Yeah, and I guess that’s the real question that needs to be resolved. Is there even any actual measurable difference between weather on one side of a river or highway vs. the other, or is it just confirmation bias based on weather forecasters conveniently choosing a known highway or geographic feature as a dividing line.
A very quick google “Do roads affect weather” yields many results saying roads are used by meteorologists simply as a convenient descriptor. When other descriptors, such as mountains, are used, they DO affect weather systems. Also mention the incidental effect roads have in contribting to heat islands, but that is not what you are asking.
A few years ago, I was in Lebanon, NH. It had been snowing the day before, when we left Vermont, but things were just slushy when we crossed into NH - the border is the Connecticut River. When we went back to Vermont the next morning, it was slushy in NH and no active precipitation. The minute we crossed the river, however, it turned into light snow again, and no slush. IIRC, the terrain is somewhat hillier on the Vermont side of the river right there.
My assumption is that the terrain difference was responsible, and the river was there because of the terrain.
I’d never seen nor experienced such a gradient in temperature / weather until then.
A few years back, there was a tornado in northern Virginia, that basically tracked northward along I-395. I think that was coincidence, and as others have said, just a convenient way of describing a path. I drove that highway just a few minutes after the tornado had gone by, and saw no evidence that it did any damage there.
Riding home at night cross country on my motorcycle, and being too stupid to take a jacket with me (because it’s warm during the day) really showed me temperature differences between the tops and bottoms of hills. Maybe a big enough river could affect weather by being a lot water in the lowest geographical location, often in a valley.
My regular golf course is along a very small river (DuPage). The valley is not dramatic or huge. But quite often when I golf early in the morning it will be clear at home but foggy at the course. I didn’t think that was what the OP meant in terms of “affect weather.”
I’d say this is the most plausible answer. Transportation follows rivers and valleys, especially in hillier terrain. Weather is more likely to follow those same corridors.
There’s a subtle but noticeable change in weather on either side of the Ohio River. It’s not immediate, but within 20-30 miles it gets noticeably colder and windier north of the river. Dayton Ohio for instance is several degrees colder on average (more so in winter) and significantly drier than Cincinnati. The thing is, other than occasional calm morning fog, I don’t think the river itself can really have that big of an impact on the weather beyond maybe a mile or so.
More importantly, the Ohio River is where it is because that’s as far south as the last several rounds of glaciers were able to push it. The prehistoric Ohio River was made up of different more northward-flowing rivers that were gradually pushed south and rerouted to flow west. Kentucky was simply too warm for the glaciers to advance any further, so the Ohio River marks the dividing line of a preexisting climate boundary. It’s the result, not the cause. That may explain why it tends to be windier north of the river too. The glaciers scraped much of the terrain flat, so winds are unimpeded. Kentucky’s deeply eroded hills tend to deflect the wind up away from the surface.
A river is easy to identify as a line of change in the weather but many large rivers are at the bottom of a large valley and it will be the valley that affects the weather more so than the just the river.
Yeah, there have been a few times I’ve been flying into my hometown of Cleveland, and seen a solid bank of clouds over all the land, ending sharply right above the shoreline.