Wednesday, December 3, 2014

Simulated Lake Effect Nov 18

Below is an animated gif of the NSSL-WRF forecast from Nov 18, 2014 at 0000 UTC of the 0-3km Updraft helicity (hourly max) during the Lake effect snow event. 
Numerous vortices were shown on radar animations over Lake Erie which dumped a bunch of snow on Buffalo and points further south. So I wanted to see if 0-3km UH could resolve anything associated with the vortices. As you can see below it appears the band over Lake Erie did not have any features but the band over Lake Ontario did. Granted the values are very small, below 6 m^2s^-2, but given how small the bands were I am surprised anything showed up. This is another example of effective resolution. If the bands are too small, below 7 delta x, then it is likely the model filters are damping the circulations. This is not the fault of the model per se, it just means the model is not capable of predicting such fine scale features at this particular grid spacing. As for the bands that are present, they are 3-5 dx in width in the along wind direction. They are probably being partially resolved because they are features that are big.
The event in question for the tughill plateau resulted in 6 (south) -18 (north) inches of snow. You can see the 0-3km UH transition from focused north and into the Tughill and then later drift southward and reorient. I will update later with a reflectivity animation and discuss this more (and probably swap out color tables - too many meetings this week).