Barrier jet

There is strong evidence here that a barrier jet was enhanced by the north-south gap along highway 108 in the area of the Beaudoin farm. Barrier jets occur when strong westerly flow interacts with North-South mountain ranges to generate strong southerly winds to the west of this terrain. This would have been further enhanced by the storm outflow associated with the approaching hook echo and mesocyclone. This interaction could explain the exceptional winds generatd by the storm as it crossed Highway 108.

Damage on the Beaudouin farm

The Beaudouin farm sustained what is perhaps the most devastating damage, losing several cows, a new barn roof, and severe damage to a small old barn. Fortunately, there were no serious human injuries.

Eyewitnesses reported severe southerly winds during the most frightening times. These winds blew a farmhand within the small barn inside the building. These winds also blew this tractor attachment (about 100 lbs) about 10 feet northward along the ground.

Damage on easterm side of gap

The damage pattern on the eastern side of the gap shows a different story. This picture taken from the Beaudouin farm shows that the trees at the bottom of the gap did not escape damage, with most falling towards the north (left on the page). This indicates strong southerly winds acting to uproot these trees.

Higher along the ridge, some trees also have fallen paralell to the gap (northward), but others are leaning away from the camera and to the right, indicating that both westerly and southerly winds damaged this area.

Eyewitnesses from the Beaudouin farm confirmed that pieces of the roof from the barn (a tarp-type roof) were found 1/2 to 1 mile away in this direction, indicating strong westerly winds aloft.

Damage on western side of gap

This image shows the most obvious damage looking west across highway 108. The Beaudoin farm is to the left of the image. Notice that the trees on top of the ridge are sheared off on the middle and have fallen towards the camera (eastward), indicating damaging westerly winds. Trees in the lee of this ridge are not damaged. This indicates that a gust of strong westerly winds shot over the ridge, damaging the trees on top, while leaving trees below unscathed.

Storm track and topography

The survey of the NWS Office in Burlington Vermont has prepared a map showing the damage path associated with the July 18 storm. Lighter shading indicates damage consistent with winds in excess of 50 to 60 mph, whereas darker shading indicates damage consitent with winds between 70 and 90 mph with possible gusts up to 100 mph. The yellow "T" mark the position of possible EF0 and EF1 tornado damage along North Cambridge Road and Highway 108, respectively. The damage path runs 6-7 miles long. The worst damage occured in the hollows and valleys running perpendicular to the storms path. This implies strongly that topography had a significant impact on the dynamics of the storm.

Locator Map

On Wednesday 30 July 2008, I visited the vicinity of the Beaudoin Farm along Highway 108, as well as the site of wind damage along North Cambridge road. The Google Earth depiction below shows the terrain features of the site as viewed from the north, including the Beaudoin farm and location on North Cambridge Rd. where the video of the storm was recorded through an east facing window (facing left on the image) . Both locations are in north-south valleys separated by a ridge that rises 140-270' (40-80m) above valley floors.

Introduction and References

On July 18, 2008, a severe thunderstorm with estimated winds in excess of 100 mph (160 km/hr) touched down in North Cambridge, Vermont. It uprooted and snapped numerous trees and caused extensive damage to a small farm along Highway 108.

Eyewitness accounts indicate that high winds lasted about 5 minutes and were characterized by strong southerly winds followed by an abrupt shift of damaging winds to the northwest. The wind shift was documented in cell phone video.

On July 28, 2008 the National Weather Service, after field investigations declared that and EF1 tornado touched down twice between 3:27 and 3:35 PM EDT (19:27 and 19:35 UTC) and on July 18th as its path crossed North Cambridge Road and Highway 108.


View Larger Map

Power Point Presentation
Storm overview

Local News Reports:
WPTZ (NBC)

WCAX (CBS)
Video of Storm Passage (8MB avi)

National Weather Service
Storm Prediction Center Summary
Storm Report from Burlinton, VT


Storm Prediction Center
Convective Outlook
Mesoscale Discussion (18UTC)
Mesoscale Discussion Graphic (18UTC)

COMET Modules
Barrier Jets
Gap flows