Spring across the Higher Summits

2017-03-26 17:30:59.000 – Adam Gill, Weather Observer/IT Specialist

 

Spring at high elevations will always come at a later time than in the valleys. The summit of Mount Washington will still have snow on it after many of the plants in the valley have started to green up. There are several factors as to why that is!

First of all, being at a higher elevation, the temperature in the atmosphere cools with height. This is known as a lapse rate and the average lapse rate is 6.5°C per kilometer or about 3.5°F per 1,000 feet, and can be as much as 5°F per 1,000 feet! The summit sits about 5,000 feet above the base of the autoroad and almost 6000 feet above North Conway so we will usually be between 15-30°F colder than the valleys! As you can imagine, this cooling with elevation will cause us to see an early winter and a late start to spring and summer. So when it is 60°F in the valley, make sure to check out the summit conditions page to make sure that you are properly prepared for all the weather you will encounter.

Another reason is because warming in the upper atmosphere is delayed and takes a little bit for the warming surface to mix to higher elevations. Below are a few charts depicting the annual temperatures at 925mb(~1,500 feet), 850mb(~5,000 feet), and 700mb(~11,000 feet). In February, the average temperature begins to increase at 925mb because it is closest to the ground and will be influenced by solar heating first. At 850mb, it does not see a significant increase in temperature until late in February into early March. Finally, at 700mb, the warm up does not really get going until mid-March.

 

 

 

Adam Gill, Weather Observer/IT Specialist