Lowest unofficial low

[Tony Perkins]

I overheard some strangers walking by who were discussing an unoffical low of -140F on Mt. McKinley. All I heard was that there was a recording device up there that was forgotten about, that didn't record any time stamps. It was then forgotten about.... When it was rediscovered, it showed that a low of -140F had occured at some point.

This sounds a bit like a story that got exaggerated over time or may have been elsewhere, as I could not find any reference to it on the web. I did however read that Mt McKinley is one of the coldest mountains in the world, so maybe it isn't so far fetched.

Has anyone heard this tale before and have details on it?

 

[Tim Vasquez]

I call BS on it. Extreme low temperatures of -40F and below tend to require a shallow inversion-capped layer close to the ground, strongly influenced by radiational cooling, insulated by snow cover, and calm winds to minimize turbulent flow; I have serious doubts this could develop on a mountain even in the best conditions. And as far as the synoptic-scale flow, I think -50 to -55C is about the lowest 500 mb (15-20Kft) temperature that would typically be seen on the maps, -60 to -65 would be pushing it. And that would require the mountain to be in a large-scale polar vortex of some sort with really low heights, so the winds aren't going to be calm, and there won't be localized temperatures getting any lower than that.

I think the claims of -140F come from the same crockpot where tall tales of -100 pseudo-wind chill temperatures in North Dakota come out every winter.

Tim

 

[B Ozanne]

There's a book called "Minus 148" by Art Davidson that chronicles the first winter ascent of Denali. It's called Minus 148 because that is how could the windchill was while they were climbing, it had nothing to do with the actual air temperature.

Tim is right though. Mountains are cold on average, but when it comes to extreme cold they just don't compare to the valleys. Dig up some soundings of polar air over Canada right now and you'll quickly understand how shallow those cold air masses are.

One exception that doesn't seem to fit is Mount Washington in New Hampshire. They hold the record low for the state at -47F. In the winter they hover just below the 800mb level.

Edit: That book title was dreamed up before the revised windchill chart was released a few years ago.