In part 2, I'll discuss the perception of a possible bust. The 12z model runs on March 20th looked really good for the second wave. Below are various snowfall plots for the the 12z 03/20 runs for various long- and short-range models. I use Kuchera when possible, and the ICON calculates its own ratios. Others are 10:1, or just qpf as snow. I show show both the total snowfall and the first 12 hours of snowfall (mostly from the first wave). The difference between these two is roughly the snow from the 2nd wave.
Most models looked really good for the 2nd wave. The Euro got a lot of attention. Even though its total snowfall number included too much from the first wave, it also generally had too much from the 2nd wave. But it wasn't alone. Of all of these runs, the ICON might have been closest to verifying. I've noticed that the ICON rarely spits out real weenie runs. I'm not sure why, but a couple of thoughts:
1. It calculates its own ratios, so we never see a 10:1 ICON map. On the other hand, we only ever see 10:1 HRDPS maps.
2. It's non-hydrostatic, so perhaps it's less prone to convective feedback issues? That's a total guess, but I'm curious if anyone here knows whether it's true.
By 00z, it was clear that 12z had been overdone. One of the things I noticed at the time was that that the RGEM trended towards its ensemble mean. Here are the 00z 3/20, 12z 3/20, and 00z 3/21 ensemble means the second wave (starting 00z 03/21) for the RGEM.
Generally a good agreement for a widespread 0.4" - 0.7" qpf as snow.
The 12z 03/20 RGEM was well above what was shown above, and it steadily trended down from 12z to 00z. (I didn't have all the right files to make these plots, so the times and amounts are slightly off, but it's close enough.)
The actual total precip for the 2nd wave was close to both the ensemble mean and the 00z RGEM. (This is total precip, but most fell as snow.)
This is the first year I've really followed the RGEM ensemble, and I had been wondering whether the RGEM would tend to trend towards its ensemble, as the global ops often do. This was a pretty good example where that appeared to happen. That's one of the reasons I wasn't too worried about this being a total bust. The RGEM ensemble had been fairly steady, and it indicated that there would be widespread 0.4"+ qpf as snow. The below maps show 12z RGEM ensemble probabilities, for just the bulk of the 2nd wave (00z 03/21 to 00z 03/22).
Even though many of the other 12z models appeared to be more generous with snow, I found the above maps useful for my own expectation-setting.