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NAM frontogenesis and EPV
The data on this slide shows NAM forecast 850 mb frontogenesis (green contours) and 500 to 300 mb EPV (negative values shaded blue, weakly positive values (< 0.1 PVU) shaded purple) valid at 18 UTC on the 2nd. The data on this slide shows a large area of weakly positive EPV located above and on the warm side of a low-level (850 mb) frontogenesis maximum. That configuration is favorable for an enhanced frontogenetical circulation, and heavy precipitation on the warm side of the frontogenesis maximum (in this case, the warm side of the frontogenesis would be over eastern Pennsylvania).