Response from NWS in Burlington, Vt.
They aren't even sure what happened.
Dave,
You're observations are spot on, and to be honest, that is part of what made the event rather unique. In all honesty, we still aren't totally sure about all the specific details that resulted in what happened -- it's something we hope to figure out sometime in the near future.
What we do know ---
During the afternoon we had a band of 50-65 mph winds between 3000-5000ft move northward across Vermont. This is not uncommon. The winds were blowing from southeast to northwest, and when they interacted with the steep terrain of the Green Mountains, they created mountain waves (analogous to ripples in a river as they move over rocks). The mountain waves act to bring stronger winds closer to the ground. However, most of the afternoon, even with the mountain waves, the strongest winds still remained well above the ground or restricted to the highest elevations in the mountains. Down at low elevations, such as in Rutland, we typically see a breezy conditions with gusts of 20-30 mph from the east in these situations. This is what we had in our forecast.
The short period of rain that moved into the Rutland area in the late afternoon were the remnants of heavier showers and some thunderstorms that occurred earlier in the afternoon across northern NJ. Our belief is that as the decaying showers interacted with the mountain waves already occurring, the environment changed such that the mountain wave turning into a breaking wave (analogous to ocean waves as they turn into breakers when reaching the beach). These breaking waves are more violent, and brought these strong winds right down to the ground. Just like waves on a beach that surge back and forth, these breaking waves will result in surges of wind. I'm guessing that is what you may have observed as well. Based on the observations we had, the period of damaging winds only lasted about 45 minutes.
Hopefully this makes sense. Although we expected those stronger winds above the ground to occur, we did not expect the exact conditions to come into play as they did to result in the winds making it to the ground. It ended up being a rather localized event that was likely due to just the right combination of factors that are very difficult to forecast in advance. Thus our desire to do additional research on this particular event so we can do a better job next time.
If you have any questions, please feel free to email me.