January 2010

Throughout the winter arctic air masses move in over Lake Champlain. Frequently, a layer of fog develops at the interface between air and water. At first the fog is formless, but then a few strands will be pulled upward in strings like cotton candy. The wisps of steam carry heat and moisture to the air above. Occasionally, some of these strings begin to spiral and become taller and tighter, stretching up above the fog layer. The thin tubes are typically only a few feet wide, but can get much larger. The tubes can reach up to a hundred feet into the air, like small tornados over the lake. 

The whirlwinds, usually referred to as steam devils, form via the same process that creates the little dust devils that whip across a parking lot or driveway on a summer’s day. It requires a layer of cold air sitting over a layer of warm air, and a breeze or wind. For the dust devils, the blacktop of the driveway absorbs sunlight and creates a warm layer underneath the air above it. For the steam devils, the warm lake underneath the arctic air mass provides the warmth. 

The wind creates a pressure differential between the two layers and pockets of low-pressure air sometimes develop in the upper layer. The steam flows into these pockets as the wind rotates it and the column becomes stretched. More warm air flows in at the base of the spiral continuing to fuel the steam devil. As the air rises, it cools and displaces other cool air which streams down the outside of the funnel stabilizing it and squeezing the column of rising air. The fog begins to act like an ice skater pulling her arms in during a tight spin, it rotates faster and faster. As the warm air at the base is eventually displaced by the cool air flowing downward, the system loses stability and collapses. Thus the steam devils are short-lived, few lasting longer than a few minutes.

A 1972 description of steam devils on Lake Michigan observed from aircraft noted the presence of “quasi-hexagonal cells elongated along the surface wind direction.” The largest steam devils formed at the vertices of the cells.

Lakes are not the only places steam devils form. They can also be seen in the plumes of power plants and over hot springs. Another similar phenomenon is a fire devil. These occur in the heated air above forest fires and other conflagrations.

The steam devils serve to transfer warm air and moisture to the cold air above the lake and are a first step in the formation of advective cumulus clouds often seen once the air has sat over the lake for a time. 

A water spout is a similar, but more substantial example of a steam devil. These are more common in the tropics where cold air more commonly moves over much warmer water. However, they have been observed in temperate lakes. In January 2009, Andy MacDougal of Essex, NY recorded two on Lake Champlain. Water spouts tend to be stronger and longer lived than steam devils. The critical distinction, according to the National Weather Service, is that a water spout reaches all the way to clouds that have formed above the lake as the fog rises. As a result, water spouts can be 10 times taller than steam devils. 

It is likely that steam devils and water spouts are more common on Lake Champlain than most people appreciate. The weather conditions that produce the phenomena, a combination of arctic cold and wind, prevent most people from straying outside too long.

One person who has had the opportunity to observe the spouts on numerous occasions is Gary Kjelleren. His office sits in the fourth floor of a building only a few hundred yards from Lake Champlain with windows running the length of it offering unobstructed lake views throughout the year. He sits with his back to this wall to avoid the distraction of the ever changing vista. Recently, when conditions were favorable for steam devil formation, he invited me to visit his office. Smoke from nearby stacks travelled horizontally due to the cold north winds as we watched several rise out of the steaming lake waters between the Four Brothers and Juniper Island. Gary described watching the mini-tornados make landfall and rattle the dried leaves left in shoreline trees.

As winter progresses and more of the lake freezes, steam devils become less common. However, so long as there is open water, the phenomena might be seen when the coldest weather enters the region.