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500-300 mb Div Q and 850-700 mb Fn divergence (February 13, 18 UTC 00-24 hr NAM forecast)
Notes:
The data on this loop is similar to the data on the previous slide, except that Fn vector convergence is indicated by the shading, instead of frontogenesis. Fn vector convergence is the forcing for upward motion due to the frontogenesis. The main point of this slide is that the Fn vector convergence intensified when it became juxtaposed with upper-level Q-vector convergence during the afternoon on the 14th. The heaviest snow fell during the afternoon on the 14th.