Mount Washington: Breaker of Storms
2018-09-08 09:27:36.000 – Sarah Schulte, Museum Attendant
Each season brings with it new meteorological wonders for weather nerds to anticipate, and summer is certainly no exception. While the winters on Mount Washington are great for rime ice events, torrential snowfall and fierce winds, the summer season is a prime time for thunderstorms. Whenever the potential for a nice line of cells crops up in the models, everyone begins to cross their fingers in anticipation for a natural light show…
…only to have their shoulders slump in disappointment when the cells sputter and die upon approach of the mountain. The weather is taunting us!
Unfortunately, this aggravating behavior can’t be blamed on Mother Nature’s malevolence. Mount Washington has a tendency to either make or break a thunderstorm, and in either case, the thunderstorm isn’t usually happening directly at the summit. This isn’t to say that we never see a storm at the summit; as the tallest metal object around, our tower and deck make an attractive lightning rod. In fact, thunderstorms are the only conditions in which the weather observers won’t venture outside for their hourly observations. However, this does mean that getting extremely hopeful at the sight of every approaching system can be a good setup for disappointment.
So, why does Mount Washington have this power?
Making (and Breaking) a Thunderstorm
Mount Washington isn’t special when it comes to generating and destroying storms. The cause of thunderstorm formation at the approach of a mountain is orographic lifting. Orographic lifting is the ascent of an air parcel due to terrain. As air is pushed up against the side of the mountain, it’s forced to rise. The air parcel cools as it rises, which means a moisture-laden air parcel will condense and create precipitation. In the case of Mount Washington, the elevation is high enough that the storms are often drained of energy by the time they reach the summit. Thunderstorms essentially get wrung out like sponges as they climb mountains (just like people!), and while they might still have precipitation to give when they crest, they tend to lack the energy necessary to light things up like they did upon approach.
Some taller mountain ranges, such as the Rockies in the Western US or the Himalayas in Asia, drain clouds to the point where their precipitation reserves are completely spent by the time they reach the peaks. When this happens, the mountain range can create a rain shadow, which is a dry region to the east of the peaks. Because the mountains inhibit the passage of clouds, the areas to the east receive very little rain, hence the many deserts to the east of the Rockies and the Tibetan Plateau east and north of the Himalayan Mountains.
This thunderstorm making/breaking ability is another reason why checking the weather before a hike is very important. One of the ingredients of a thunderstorm recipe is warm, rising air, and in the summertime, the White Mountains absorb enough heat and cause enough lifting on their windward sides to brew up some dangerous weather. And since the elevation of the White Mountains isn’t staggering, these storms won’t necessarily peter out as they crest, especially on some of the lower slopes.
For the weather nerds working up here, this phenomenon can lead to some incredible sights, such as an afternoon several weeks ago where the summit was in the clear, and there were thunderstorms brewing all around us. On the other hand, it can also lead to very anticlimactic storm events, or frustrating moments when the cell reorganizes after it passes over the mountain. As of now, I still haven’t learned my lesson, and I know I’ll continue to get excited whenever the possibility of a good show rises up our windward slope!
Sarah Schulte, Museum Attendant