Fog – More Likely Than Not

2015-07-30 15:23:51.000 – Thailynn Munroe, Summit Intern


Wow! I can’t believe that I only have one more shift left on the summit. This internship has been challenging, mentally and physically, but it has also been more than rewarding. I really enjoy being able to practice my forecasting skills and observe whether or not I was accurate. For most of the first half of my past shift, the forecasts were relatively easy because the summits were in the fog.

The higher summits see so much fog because of orographic lifting (in essence, the lifting of air due to terrain). Air at the surface of the Earth carries some amount of water that usually exists as vapor. As you or the air travels up the side of a mountain, you are also travelling through some of the atmosphere’s mass. You will observe a decrease in pressure (roughly 20% on Mount Washington, but up to 70% on Mount Everest!) because there is less mass sitting on top of you. This in turn allows the air to expand and cool. If the air is cooled enough, specifically to the dew point temperature, the water vapor in the air will usually condense into small droplets, which forms the fog we so regularly enjoy up here. That same process is also the mechanics for lenticular clouds, which many people liken to UFOs near mountainous terrain.

Being in the fog for so long makes being days in the clear 1,000x better because you appreciate them so much more. Some days the fog is so thick you can barely see 30 feet in front of you. That makes retrieving the precipitation can challenging and sometimes pretty eerie when you can hear people talking around the summit, but you can’t see them. However, when the clouds break, lift, or drop below us (which we call “undercast”), you can literally see for over 100 miles (pending on haze). So if you visit Mount Washington when we are in the fog, try not to get too frustrated, because you are experiencing a phenomenon that the summits experience over half of the year. If you come up and we are in the clear, just know that you are lucky, and enjoy the views!


Thailynn Munroe, Summit Intern

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