Why do we have weather that comes from different directions?

Factual Questions
1

(I am in Wisconsin, USA)

When looking at the weather channel, storm systems ALWAYS come towards us in a southeastern direction. I assumed this was either because of the Earth’s rotation or the jet stream.

However, all of these hurricanes that happen in the southern US, tend to follow a East to West direction, with some actually heading North once it reaches the mainland.

So what causes weather direction? Jet Stream, rotation? Or do storms sort of act independent of what is happening on the ground?

2

I’m sure someone will come up with a more detailed scientific answer. But the short answer is that all weather is basically warm parts of the Earth trying to reach equilibrium with cold parts. Since the Earth both rotates and tilts on it’s axis, those warm parts change at various times. Other factors like the Coriolis effect, geography and placement of land and water masses effect things as well. For example, hurricanes always form in the warm part of the Atlantic north of the equator and tend to move west and north. The equator itself tends to be very calm (see “Doldrums”). Heavier cold air tends to push down from the poles. So on and so forth.

3

The atmosphere is pretty complicated, but for an oversimplification, the air at the equator tends to move east to west, the air at higher latitudes tends to move west to east, and the air at the poles tends to circulate to the west. At the same time, the air at the equator tends to rise due to heating, where air at higher latitudes tends to fall due to cooling. So you’ve got a lot of complex circulation going on. It’s even more complex than that as air can rise from higher latitudes as well, so you end up with loops of circulating air at various latitudes.

Hurricanes start out in the tropics, and as such they start out following the prevailing east to west air currents, which are also going a bit northward. As the storms get pushed north, they follow the circulating air currents and curve around northward, then northeast, then west to east as they reach higher latitudes where the air is moving mostly west to east.

The air currents aren’t nice and even. There’s more than one jet stream, and they tend to meander quite a bit. There’s a polar jet and a subtropical jet in both the northern and southern hemispheres.

See this pic:

So you’ve got those basic movement patterns (east to west, then west to east, then east to west again depending on latitude), but the whole thing is pretty chaotic, as that picture of the meandering jet streams shows. It’s even more complex than that, because things like land masses which hold heat and oceanic currents which distribute heat in various patterns also all come into play.

In general, weather across the US tends to follow a west-to-east pattern, but there’s a lot of variation. The variance in the meandering jet streams can bring tropical air up from the south or cold polar air down from the north. In the eastern US, it’s also fairly common for storms to circulate around the Atlantic, following the same sorts of patterns that you see in hurricanes, first moving west, then curving north and east. Often this brings heavy rains or snows up the eastern coast of the US.

I don’t know much about the weather in Wisconsin, but I’d expect the jet stream to bring you some cold weather from the North at times, depending on which way it happens to be meandering.

4

This is a cool website.
http://https://earth.nullschool.net/#current/wind/surface/level/orthographic=-107.91,50.17,3000/loc=-114.091,51.060

You can see the air movements at different altitudes using the menu. You’ll notice how the movement often follows ocean currents and along some mountain ranges too, depending on altitude.

5

Exactly so. In the winter, Wisconsin will regularly be affected by “Alberta Clipper” storms, which come down from the northwest.

6

One note: “Earth’s rotation or the jet stream” is a false dichotomy. Jet streams form as they do because of the Earth’s rotation, as well as the heat differential between poles and equator.

7

One very important aspect of the circulation of the atmosphere is the existence of circulation cells, which consist of the Hadley Cells near the equator, carrying heat away from the equator, and the Polar Cell, carrying cold air away from the poles. In between is the zone of mixing, which is where most of us live and experience the sometimes chaotic effects.

The jet streams are associated with these vast rotating cells, and the interaction between the Jet Stream and the three atmospheric zones are what cause a very large fraction of our weather. Of course topgraphic effects have a large influence too, especially in the Gulf of Mexico, along the Andes and Rockies, and around the Eurasian massifs; but these effects are modifying the basic circulation, rather than the cause of it.

8

As a weather watcher and fellow Wisconsinite, storm systems do not always come from the southeast. The majority roll in from the west (with various components of north or south vectors added in), but every autumn we get a fair number out of the northeast too. The Gales of November are particularly wicked, if you live near Lake Michigan.

9

Cyclones spin counter-clockwise … if the largish cyclone (moving west-to-east) is sitting to the southwest of Wisconsin, then the surface winds will be blowing from the southeast … the storm is coming from the west, but due to the circulation, the winds come from the southeast is all … if there’s a warm or cold front then the surface wind direction is even more confusing …

10

Hence, the famous term in New England coastal areas, the “Nor’ Easter”, which does not mean that the storm moves from north-east to south-west, but rather that, as the storm moves eastward (usually to the north-east), the direction of the wind circulating around the low comes out of the north-east, along with the rain/snow bands.

In Wisconsin, almost all fronts approach from the west, or the north-west. Sometimes, the front will come up from the south-west. It would be rare in the extreme for a front to move into Wisconsin from anything other than a westerly direction.

11

One simple thing to do to better understand weather patterns, is to ZOOM OUT to the national picture.

A lot of the time, the reason why a weather effect SEEMS to be going “against the grain,” is because it’s part of a much larger system that is rotating in some places. If all you look at is the local picture, you wont realize that actually the edge piece that’s sweeping in from the south, is actually just a tiny part of an overall system that is moving TO the south.

12

But does Michigan give up her dead when those Gales of November come early?