omega block
 n.— «Northern California has been sitting under what meteorologists commonly refer to as an “omega” block—so named because of its distinctive shape—which features troughs of low pressure both to the west and east of a large bubble-like ridge of high pressure situated directly over the top of us and extending well north into British Columbia. This is a very stable pattern which is difficult to break once established, and it tends to lead to a prolonged spell of calm, dry weather as systems ride up and over the top of the ridge into Canada before plunging southward towards the United States into the upper Midwest, bearing frigid arctic air pooled up over the frozen tundra of our neighbors to the north.» —“Fair weather expected as ‘omega’ block continues” by Jeff Popick St. Helena Star (California) Jan. 17, 2008. (source: Double-Tongued Dictionary)

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