Even the cloud bands have largely dissipated. The weakening as occurred even as the temperatures have fallen at mid levels (e.g., ~500 mb) and as wind direction, temperature, and dewpoint on Promontory Point have barely changed.
So what gives? It appears that unresolved (by our data network) mesoscale processes or "don't know squared" is in operation (i.e., it is what we don't know we don't know that makes this problem so perplexing - tip of the hat to Michael Schlesinger for coming up with that one).
So, what could be contributing to the lake-effect decay? One possibility are changes to the lake temperature, which we unfortunately don't know because there are no real-time lake temperature observations. Another possibility are boundary layer processes. Although conditions were very steady at Promontory Point, there were major changes in the low-level kinematics during this period. For example, check out the how the wind direction at Gunnison Island veers steadily from 1345-1500 UTC from W to NE, then backs back to WNW.
Is this cause/effect or a red herring? I don't know, but this occurred at several sites, including those on the east shore that were not near the band. We've seen these sorts of transient wind shifts during lake-effect events, but they are difficult to trace. What is their origin and what role do they play in lake-effect evolution? With some supporting upper-air observations and detailed mesonet observations, this could be a good event to study for an undergraduate capstone project.
Perhaps just a little warming by the sun of the surrounding terrain was all it took to kill the convergence band? In several camera images you can see some cumulus development begin over surrounding land areas around 10 am.
ReplyDeleteThat's certainly playing a role now, but the initial weakening discussed above occurred before the land began to warm significantly. It will be interesting to dig into this and see what we can find numerically.
ReplyDeleteI wondered if that was the case... maybe I didn't look close enough at the timing. Also noticed in the WV/IR loops there was a moist band in the trough core region, extending from northern Utah back into eastern Nevada. The passage of this band around 12-14Z seems to coincide pretty well with development of the lake effect. Perhaps there was an area of subsidence behind it... will be interesting to see what you find.
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