Why do ULL often retrograde in movement?

[micktooth]

Hi all, I was wondering if you can help me. I was wondering why many ULL move from East to West in when most of the weather in the Northern Hemisphere moves from West to East? Is it due to the same spinning that moves tropical systems West to East? Thanks for all of your help.

[weatherwindow]

ULL level lows tend to move with the broad current of air in which they are embedded. at this time of year, the ULLs south of roughly 30deg N, in most cases, are embedded in a deep easterly flow hence they tend to move from E to W. there are, of course, exceptions due to the turbulent nature of upper air flow. earlier and later in the year, the westerlies sink further south which results in the typical W to E motion typical of ULL embedded in that current. again turbulence will result in many exceptions in both directions...hope that made sense.....rich