Saturday, June 18, 2016

Surprise Rogue Thunderstorm Surprised Vermont's Champlain Valley Friday Night

Web cam at the University of Vermont in Burlington, Vermont
captured lightning from a surprise thunderstorm
over Lake Champlain Friday evening.  
The weather was gorgeous in Vermont's Champlain Valley yesterday, with sunny skies, a few puffy clouds, a breeze and low humidity.

It continued a stretch of pleasant, sunny, warm weather that began Tuesday and is expected to last through the weekend.

Forecasts issued Friday afternoon did not mention any chances of rain in the evening.

Then where the hell did that evening thunderstorm come from?

The lone storm developed north of Montreal in the late afternoon and headed due south. It put on an evening light show of lightning as it moved south over Lake Champlain, passing to the west of St. Albans, and on into the Burlington area and points south.

The storm grew strong enough that the National Weather Service office in South Burlington issued a special weather statement, saying the storm would produce dangerous lightning, and wind gusts to 40 mph.

It's odd that most meteorologists didn't predict a chance of storms, but in this case, subtle atmospherics were at work to make it happen.

Remember the icky weather Sunday and Monday. Those clouds, unseasonably chilly north winds, cold rain showers and even a couple mountaintop snowflakes?

A strong storm near Nova Scotia brought on those cold north winds.

That Nova Scotia storm kept moving northeastward, away from New England, and the sunny weather moved in from the west.

But that ocean storm is still out there. That's why we've had that nice north breeze in Vermont the past couple days.

That ocean storm had just barely enough influence yesterday to add a little lift to the air. And it helped bring  a little pocket of cold air to the upper atmosphere. That created those nice puffy clouds dotting Friday afternoon's blue sky.

One of those puffy clouds grew big enough to create that shower that formed north of Montreal. The shape of Champlain Valley caused winds to converge near that shower as it headed south. Converging winds add more lift to the atmosphere, so the shower/thunderstorm grew.

On top of that, all that wonderful Friday sunshine also added energy to the atmosphere. All this combined to create that rogue Friday evening thunderstorm that disrupted a June evening on Lake Champlain.

Hat tip to WPTZ-TV meteorologist John Hickey for the help with this explanation.

That ocean storm still heading further, so it shouldn't bother us anymore. Plus, high pressure is gaining strength over us. That causes sinking air, which strongly discourages thunderstorms. So I'm pretty sure we're safe from any more atmospheric surprises in Vermont for the rest of the weekend.

Then again, you never know. There are always those subtle weather disturbances that can surprise........

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