|Slide 7 of 44|
NAM 700 mb frontogenesis and 600-500 negative EPV valid 10/25 12z
Looking now at the frontal-scale forcing during the daylight hours on the 25th: The NAM model was forecasting a distinct maxima of 700 mb frontogenesis across central New York at 12z on the 25th. Instability to slantwise and possibly vertical displacements is indicated by the negative saturation geostrophic equivalent potential vorticity (EPV), which is shaded on these and subsequent slides. The frontogenesis and instability appear to be co-located across eastern Pennsylvania, indicating good potential for banded precipitation in that area. (Note: negative EPV only implies instability to slantwise motions if the atmosphere is near saturation; in this case the atmosphere was near saturation through a deep layer (not shown)).