FORECASTING PRINCIPLES. The following empirical relationships and rules should be taken into account when you use the steering technique: . Warm, unoccluded lows are steered by the current at the level to which the closed low does not extend. When so steered, lows tend to move slightly to the left of the steering current.

. 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.

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