2015-09-07 15:03:31.000 – Mike Carmon, Co-Director of Summit Operations


Happy Labor Day to all!

It’s also our first weekly #MWOMetMonday!

Here’s our first question, courtesy of Jackie Keating, who posted the following on the Mount Washington Observatory’s Facebook page:


Pictured here is an anvil-shaped top of a passing thunderstorm. It’s clearly evident from this image that the location at which the picture was taken was not experiencing stormy conditions (like she mentions in the post, it’s a “clear sunny day”). However, intense thunderstorms can grow very large in size and vertical height, allowing their tops to be seen from many miles away.

The top of a thunderstorm gets its characteristic anvil shape because of the intense rising motion of air (or updraft) that develops within the storm. The clouds grow so tall that they can strike the top of the troposphere, which is the lowest layer of the atmosphere in which all of the weather we experience occurs. Here at the top of the troposphere, there exists a temperature inversion, which acts as an effective lid on the atmosphere. So, when this intense rising air hits this temperature inversion, the air is forced to spread out horizontally, forming the characteristic anvil shape seen in the image.

You can also tell from this picture that the thunderstorm is in a weakening phase, as it is seemingly “pinched” in the center. This is a sign of strong and cold downdrafts (or sinking air) overtaking the previously-mentioned updrafts, which inevitably causes the storm to die out.

The second question of the day comes from Tom @Patsfantk on twitter:

The El Niño Southern Oscillation (ENSO), or “El Niño” for short, is a pattern observed in the sea surface temperatures (SSTs) of the equatorial region of the Pacific Ocean. During a so-called El Niño year, warmer-than-average SSTs are observed in these waters due to natural changes in ocean temperatures below the surface. These warmer-than-average SSTs can trigger a series of domino effects that have a major impact on the weather around the world, including North America.

This year’s El Niño is forecasted to be a significantly strong event. Generally speaking, a strong El Niño year will result in wetter and cooler winters across the western and southern United States, while the Pacific Northwest and Midwestern states typically experience drier and milder winters.

Up in the Northeast United States, the effects of an El Niño year have historically varied. Temperatures are generally near-average to slightly above-average across New England. As far as precipitation is concerned, trends have generally been towards higher-than-average precipitation totals during El Niño years, largely due to the increased frequency of storm systems passing through New England as a result of the position of the northern branch of the jet stream.

It’s important to remember that we’re speaking in terms of climatological trends, so nothing is set in stone for this winter. Especially if the ENSO begins to weaken, which could buck wintertime trends back towards normal.

Thanks again for your questions, Jackie and Tom!

We’re looking forward to next week’s #MWOMetMonday!


Mike Carmon, Co-Director of Summit Operations

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