"Weak" Cold Front Turned Into A Thundery Vermont Powerhouse Thursday

A rainbow appeared as a line of surprisingly strong
rain and snow showers, some with lightning, approached
Alburgh,Vermont Thursday morning. 

Here in Vermont yesterday, we woke up to quite a benign weather forecast: A slight chance of a light morning shower as a lame pair of cold fronts arrived.

Temperatures would start out mild in the 40s and fall into the 30s Maybe there'd be a mountain snow flurry.  

The temperature trend forecast was spot on, but boy those showers had some oomph to them.

I was working outdoors along Lake Champlain in Alburgh when the "light showers" arrived. It didn't rain particularly hard, but those clouds were tall and dark and the gust front with this was impressive. And was that thunder I heard in the distance?

Sure was. Some of the showers with the cold front had lightning strikes within them. And it abruptly turned colder as the showers arrived, turning the precipitation to snow in some areas. So a few Vermonters - like those in Craftsbury Common - were treated to relatively rare thundersnow, which is always cool.

Why was this cold front so impressive? After all, it wasn't the strongest cold front ever, in terms of temperature change. It got colder after that and another weaker cold front went by Thursday, but it was nothing extreme.

This was another of those "shortwaves" I talked about in recent posts, fast moving, small storms that don't have a lot of moisture with them and don't spread rough weather or heavy rain or snow over wide areas. But some of these shortwaves can have a punch.

Every time a cold front or other weather system comes through, the air is rising, which encourages clouds and precipitation to form. But for a variety of reasons, sometimes this lift is stronger than usual. Such was the case on Thursday.

One area of this shortwave had stronger updrafts than is typical for this time of year.  Stronger updrafts can help showers grow into thunderstorms. And that relatively small area of stronger updrafts happened to pass right over northern Vermont.

Stronger updrafts mean stronger storms, so this one was able to trigger some rare Vermont November thunderstorms.

This was the second time this month that Vermont experience thunderstorms. There were some loud thunderstorms as a cold front passed on the the night of November 9-10. Two thundery days in one Vermont November is pretty rare.