Weather question

[coriolis]

From the meager amount of weather knowledge I've accumulated, I understand that the jet stream generally follows the boundary between the warm air to the south and the cool air to the north. In the current situation we have the big Low sitting over northern michigan with an occluded front all the way over to Lake Ontario. From there, a little warm front down to New Jersey, and the trailing cold front extending all the way down to texas. I can imagine the jet stream running along this cold front all the way to Lake ontario. But does the jet stream bypass that low (because of the occluded front) and continue along the warm front in a more easterly direction? In a related question, I understand that the jet stream continues all the way around the earth. But why do the weather systems seem more limited? wouldn't there be a frontal boundary extending all around the earth. Or do the weather maps just show bits and pieces as they apply to our location.
I've got lots more questions, but I'll leave it at that for now.

[ColdFront77]

Hello Ed. I will try to answer your questions.

This is my attempt at your first question: The jet stream steers weather systems, so the low pressure currently over the Michigan area isn't really related to the "west to east" and "southwest to northeast" flow.


Now on to you second issue: Say the temperature ahead of the northernmost portion of a cold front near Chicago, Illinois is 82 degrees and very humid. The frontal boundary stretches south-southwestward to just west of San Antonio, Texas; where the temperature is 97 degrees and again (obviously) very humid. The temperature behind the front is 65 at Pierre, South Dakota and 67 in Abilene, Texas. This cold front would be approximately 1,050 miles long.

Now lets take another example; say the temperature in Gillette, Wyoming and Albuquerque, New Mexico are warmer and more humid than Boise, Idaho and Carson City, Nevada... the cold front in this case would only be approximately 650 miles long, with the warm and humid air ahead of the front and the cool, drier air behind the front.

A frontal boundary ends when the temperature and/or humidity difference is closer to each other. Take Chicago, Illinois and Pierre, South Dakota... where the temperature difference is 25 degrees, with this same boundary the temperature between Brownsville, Texas and El Paso, Texas are nearly the same, that means that the cold front cannot be "drawn" further south than I indicated above.

Now lets take my second example..... north of Boise, Idaho, in Helena, Montana, the temperature is similar than it is in Spokane, Washington... thus the cold front is not any further north than Cheyenne, Wyoming.

If you have any follow up questions, let me know and I will try to answer them for you.

[coriolis]

OK Tom, thanks. I understand that the cold front can only be drawn as far as differences (boundaries) exist between air masses. But where is the jet stream coming from even further to the west. Or, in this example, maybe the jet stream isn't running along this particular boundary. Is this what is known as "zonal flow?"

[ColdFront77]

You're welcome, Ed. You knew the answer to your first question... Knowing that fronal systems end because the difference between air masses at two locations south of the southern portion of a boundary than you can see why cold fronts aren't continous.

The "zonal flow" is the flow of air along a latitudinal component of existing flow, normally from west to east.