• Motion due to continuously evolving pattern of forcing
  • topography can cause motion accross ht contours: (recall section 9.2: low slides south along east side of Rockies even though 500 mb flow is westerly.)
  • developing storm moves in direction of greatest QG thickness advection (recall eqn. 7.3). From relation between thickness advection => vertical motion => surface convergence, this is similar location as region of greatest surface convergence. Either way, system follows h contours.
  • development may be geographically enhanced => low appears to move to where it is deepening most rapidly. Recall these 3 situations:
    1. low static stability argument (section 9.2 over TX) makes vertical motion easier, hence a given forcing results in greater vertical motions => greater energy growth of storm, etc.
    2. over western boundary currents (WBCs) => source of heat to reduce static stability, moisture source to enhance storm energy.
    3. on lee side of mountain range. => lee side trough.

• Empirical rule: developing surface lows tend to move in direction similar to 500 mb flow at about 1/2 the geostrophic 500 mb wind.

• Mature low hardly moves because max surface convergence migrates to cold air and quite close to current location of surface low center.

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