Nor'easter jetstream vs. clipper?

[Ice Man]

So, I've been feeling like a confused noob as of late. Each time I saw the jetstream map last week, the kid in me jumped a little and said, "Hey, that's a nor'easter jetstream." For a moment I'm excited, waiting for a low to start circulating in the Gulf of Mexico, and then they cut to the news about the near-endless stream of Alberta Clippers. What is confusing me is the jetstream looked exactly like what I remembered seeing at times where Nor'easters were common. But any low pressure following the initial jetstream failed to travel south, and instead 'jumped' the trough, shooting across the Great Lakes. This was happening even when the trough dipped as far south as Alabama. From what I remember of "Clipper" jetstream patterns, the trough is subtle, dipping only slightly below the lakes.. which more like what we're seeing this week.

So, what crucial Nor'easter ingredient is it that I'm forgetting about?

[phw115wvwx]

Alberta Clippers follow the polar jet stream but are starved of moisture as a result.  They are following along the periphery of the polar low currently over the Hudson Bay.  However, the upper level trough associated with this polar low is pushed so far south in the eastern United States that the subtropical jet stream (yes, there are actually two of them) is shunted way to the south.  Thus, the Gulf of Mexico is essentially shut off from being tapped into any systems, and the polar jet stream is dominating the pattern over the Eastern United States.  Thus, the Alberta Clippers cannot make a good Nor'easter, but they are quite common.

For a Nor'easter, you need to have a low pressure system that eventually phases together energy from the polar and the subtropical jet streams.  There needs to be ample moisture from the Gulf of Mexico and/or the Atlantic Ocean.  You cannot solely rely on where the jet streams are located.  You need upper level disturbances riding along them to come together with ample moisture to intensify in a favored environment for your Nor'easter to develop.  It's just not that simple, which is why they are rare.

[Ice Man]

Ah, that's it, the presence of the Pacific and/or Subtropical jet. Now that you mentioned that, I can vaguely remember the maps often showing two jet streams any time a Nor'easter was coming. Thanks for the refresher course.