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23/00 UTC Eta 6-hour forecast cross-section of frontogenesis, relative humidity and EPV, taken across eastern New England at 23/06 UTC.
In contrast to the cross-section shown earlier in this presentation, this cross-section shows a large area of negative EPV collocated with relatively deep saturation above a pronounced area of frontogenesis. Recall that the cross-section taken 6 hours previously, over central NY, was associated with a narrow band of negative EPV in a region of relative humidity mainly between 60 and 80 percent. This cross-section is the type of cross-section typically associated with CSI, and extreme snowfall rates (note that snowfall totals over portions of eastern Massachusetts exceeded 30 inches).