Undercast at Sunset

2013-07-29 15:44:06.000 – Luke Davis,  Summit Intern

Ocean of Clouds

It’s been another eventful week on the rockpile. Arriving at the base last Wednesday, at 8 A.M. and after 5 hours of driving, I was as tired as ever. We were socked in by the time we reached the summit, and it seemed like another dull, drizzly day was in store. But one thing I’ve learned here is to always be prepared for the unexpected, and to know that the dullest days can turn into the most extraordinary in an instant. In this case, a thick fog we anticipated to last through most of the night broke up just before sunset, unveiling one of the most incredible sights I’ve ever laid eyes on. I had always dreamed of seeing it, and there it was — an expansive, unbroken undercast. We were the only point above the clouds for dozens of miles.

Undercast, or solid cloud-cover beneath the point of observation (analogous to an overcast, which indicates cloud cover above the point of observation), is more common during the winter months, but can occur in the summer given the right synoptic conditions. A few elements are at play — plenty of atmospheric moisture near the surface must be coupled with a strong temperature inversion and dry air aloft. Temperature inversions are situations in which temperatures rise, rather than fall, as one gains height through the atmosphere, and have the effect of ‘trapping’ whatever particles are below them — such as water droplets.

This time, a unique series of events allowed for this very setup. A low pressure system had just passed the region, its warm front delivering plenty of showers and bringing high humidity levels to the valleys. However, the cold front associated with this system, packing very cold, dry air, began to overtake the ‘warm sector’ behind the warm front, with the warm front entirely dissipating. Having a higher density, this cold air bulldozed underneath the warmer air we had just seen, sending it aloft. The cold air became bunched up against the leading edge of the front to create a ‘bubble’ of particularly chilly air rising well above the summits, causing temperatures here to drop toward 37 before sunset. Low-level moisture began to condense, creating low clouds, due to the cooler air present, and low-level temperatures would continue to drop through the night — however farther behind the leading edge of the front, the cold air layer was far shallower, and the overriding warm air, whose moisture had been entirely precipitated out, began to extend deeper. Droplets near the top of the cloud layer evaporate upon meeting this boundary — the inversion boundary — which dropped below the summit just before sunset. At the time, we saw a temperature spike of 10 degrees in 15 minutes, and finally emerged from the fog.

When we noticed the undercast, everyone ran outside. Buffeted by 40 mile per hour winds and temperatures still well into the 40s, we put dinner on hold to run around the summit and take pictures. Watching the sun slowly set over an ocean of clouds was like standing on top of the world, and is something I’ll never forget. It’s my second to last shift, and I can’t wait to see what other surprises may be in store.

Luke Davis,  Summit Intern