. Warm lows (unoccluded) are steered with the upper
flow if a well-defined jet is over the surface center or
if there is no appreciable fanning of the contours aloft.
. Low-pressure systems, especially when large, tend to move
slightly to the left of the steering current.
. Rises and falls follow downstream along the 500-hPa
contours; the speed is roughly half of the 500-hPa
gradient. The 3-hour pressure rises and pressure
falls seem to move in the direction of the 700-hPa
flow; while 24-hour pressure rises and pressure falls
move with the 500-hPa flow.
. Cold lows, with newly vertical axes, are steered with
the upper low (in the direction of upper height falls),
parallel to the strongest winds in the upper low, and
toward the weakest contour gradient.
. Occluded lows, the axes of which are not vertical, are
steered partly in the direction of the warm air advection
area.
. A surface low that is becoming associated with a cyclone
aloft will slow down, become more regular, and follow
a strongly cyclonic trajectory.
. Surface lows are steered by jet maximums above
them,
and deviate to the left as they are so steered. They move
at a slower rate than the jet maximum, and are soon
left behind as the jet progresses.
. During periods of northwesterly flow at 700 hPa from
Western Canada to the Eastern United States, surface
lows move rapidly from the northwest to the southeast,
bringing cold air outbreaks east of the Continental
Divide.
. If the upper height fall center (24 hour) is found in
the direction in which the surface cyclone will move, the
cyclone will move into the region or just west of it in
24 hours.
