Cutoff Low:
A closed upper-level low which has become completely displaced (cut
off) from basic westerly current, and moves independently of that
current. Cutoff lows may remain nearly stationary for days, or on
occasion may move westward opposite to the prevailing flow aloft
(i.e., retrogression).
"Cutoff low" and "closed low" often are used interchangeably to
describe low pressure centers aloft. However, not all closed lows are
completely removed from the influence of the basic
westerlies. Therefore, the recommended usage of the terms is to
reserve the use of "cutoff low" only to those closed lows which
clearly are detached completely from the westerlies.
