Weather Watch: Downsloping and a Temporary Bristol Desert
On the day before Thanksgiving, I awoke to see about what I expected to see outside - a couple of inches of wet snow.
The accumulation in East Middlebury was a bit less than forecast, but not surprisingly so. As we set off to drive to Connecticut to visit family, slushy snow was falling, with about two inches of accumulation. Along the Route 7 corridor, all the way to Rutland, snow accumulation ranged from a trace to three inches. Ludlow, a snowy town in the heart of the Green Mountains, had picked up near a foot of snow. As we headed east and dropped in elevation, I expected that snowfall totals would decrease. Instead, they remained quite high - all the way along Route 103 into Rockingham, there was at least 6 inches of snow accumulation. Even more surprising, I learned from a friend that Orwell and other parts of western Addison County also picked up about 6 inches of snow. East Middlebury seems to bear the brunt of most storms, but this time we were mostly skipped. What happened?
In this part of the world, storms tend to move from west to east. This means that everything from summer thunderstorms to chilly October cold fronts to midwinter Alberta Clippers tend to slam the west-facing slopes of the Green Mountains with heavy rain or snow. Precipitation on the side of the mountains facing the wind tends to be much higher than in the Champlain Valley. Nor’easters follow a different pattern as they move into Vermont from the southeast, but often include a period of wind from the north that can funnel rain or snow right into the Champlain Valley. It seems that every storm crossing the continent finds its way to our little town.
Last week’s storm was a bit different. It brought winds straight out of the east. As the air descended out of the Green Mountains into the Champlain Valley, in a process called downsloping, the normally-stormy western slopes of the Green Mountains became warmer and drier than their surroundings. During this particular storm we were in a ‘rain shadow’. It was almost as if Bristol, East Middlebury, and Brandon were in a temporary, localized desert. The least snowy spot in the region was actually Underhill - in this case Mount Mansfield actually sheltered its western slopes from the storm.
Wind rarely comes straight from the east during storms, so our region’s temporary desert usually doesn’t show up. The rains of this week certainly did not avoid East Middlebury. Rain and snow forecast for the next seven days don’t look like they will be blown in on an east wind either, so I’m not sure when we’ll see the return of our temporary localized desert climate.
Click here to see a more detailed version of the snow totals map posted above.
Charlie Hohn is a recent graduate of the UVM Field Naturalist graduate program. He has been closely watching the weather ever since he was a child in southern California. Charlie will be posting occasional blog posts here about Addison County weather. He also maintains a blog about water at slowwatermovement.blogspot.com.