Time-height diagram – omega and negative EPV
Notes:
This time-height diagram shows vertical motion (upward values negative (dashed), and negative EPV (shaded blue) over a forecast point at BGM. Periods of heavier snow, indicated by visibilities of less than 1 mile, are annotated at the bottom of the figure. A large area of co-located strong lift and negative EPV is indicated between 00 UTC and 08 UTC. A band of heavy snow developed during this time, with periods of heavy snow continuing after this co-located strong lift and negative EPV had diminished. A second, small region of co-located strong lift and negative EPV is indicated between 12 UTC and 15 UTC.This diagram, plus the cross-sections shown on the previous slide, indicates that heavy snow band formation occurred during a period of co-located strong lift and negative EPV, but that bands were able to maintain themselves after this favorable co-location had ended. Recent local research here at BGM has noted a similar trend in other storms, specifically that spikes in negative EPV are often observed just prior to the onset of intense banding, but not necessarily during the time of most intense banding. This is a modification of the conceptual model shown in an earlier slide, which indicates that the most negative EPV should occur through the banding period.
Slide 12