Patrol weather question of the day.

What is a closed low?

When you read that a "low pressure system" is...  It is referring to a closed low.  A closed low is a region of low pressure distinguished by a center of counterclockwise circulation (in the Northern Hemisphere), and is surrounded by one or more isobars or height contours. Closed lows aloft (i.e., above the surface) may become disconnected from the primary westerly flow and thus progress eastward more slowly. It is important to note that a cutoff low is a closed low, but it gets cut off from the main low pressure system.   This is a frequent occurance with PNW winter weather patterns.