One of the benefits of life in an arctic air mass is you might see things you just don't see anywhere else. That happened Saturday over Lake Superior, when relatively rare "winter waterspouts" danced across the big lake.
Jordan Deters was looking out over Superior near Knife River, Minn., Saturday when he noticed what looked like small tornadoes forming out over the lake. The video he captured next was a family of fairly rare winter waterspouts that formed offshore.
Thanks to Jordan for sending me the video link and some questions about what he saw.
I thought I'd share some video with you that I captured this past Saturday along the North shore of Lake Superior. We were parked along Old Hwy 61, just South of Knife River when we recorded this I believe I captured "winter waterspouts" over the lake. This is, of course, based on Internet research, rather than an educated meteorologist's interpretation.
There was definitely rotation occurring in these columns, as you should be able to see in the HD video link below. There was an abundance of "sea smoke" as well. The outside air temperature was approx -5° to -10° F. A quick search of Lake Superior surface water temps showed an average temp of +40° F. I read that winter waterspouts will occur when there is a 19° C temperature delta between the water and air, conditions that were present at the time.
I'm interested to hear your interpretation of what we saw, and if they were indeed winter waterspouts. We saw ~20 of these form and dissipate over the course of 15-20 minutes.
Best Regards, Jordan Deters
Well Jordan you pretty much hit the (video) jackpot, and nailed the explanation. Winter waterspouts are relatively rare, and not always well captured on video.
Anatomy of a winter waterspout
Winter waterspouts occur when meteorological conditions are just right. You need a bitter arctic air mass passing over relatively warm lake water, and just enough light, low level wind shear to get the rapidly rising air currents spinning nicely.
Saturday's contrast between bitter arctic air (air temp was about -7 degrees at Two Harbors nearby) and relatively warmer lake water (offshore surface water temps were around 40 degrees) create an "enhanced lapse rate" as temps cooled rapidly with height above the water. That produces rising air, and the lift needed to generate strong updrafts. Slight wind shear gets the air spinning, and small vortexes can form into waterspouts over the lake.
Here are the surface observations from Two Harbors Saturday around 4 p.m. when the waterspouts were observed.
By contrast, the water temp over Lake Superior was 42 degrees just offshore. That set up about a 50 degree contrast between the lake and the frigid air mass above.
Here's a closer look at water temps in western Lake Superior a few days before the event.
The meteorological bottom line? Conditions were perfect for offshore winter waterspouts over Lake Superior Saturday.
Winter Waterspouts over Lake Champlain in 2009
A remarkable display of winter waterspouts occurred over Lake Champlain under similar atmospheric conditions in January, 2009.
Here's a great explanation on winter waterspouts, steam devils and arctic sea smoke from the Burlington, Vermont NWS from another winter waterspout event over Lake Champlain in 2009.
A waterspout (Figure III-1) is a narrow, rotating column of air that forms over water, and appears as a condensation funnel which extends from the water surface to a cumuliform cloud above.
Formation typical requires a surface convergence line over the water, with some source of low-level rotation along the line that can be stretched vertically and strengthened by the convective cloud updraft itself. Waterspouts are generally of lesser intensity than a tornado, and similar to the strength of a dust devil. The formation mechanism is also thought to be similar to a class of weaker tornadoes observed over land referred to as landspouts.
Waterspouts are most common in tropical environs (e.g., near the Florida Keys), but have been documented in arctic air masses. Unlike tornadoes - which typically develop with supercell thunderstorms - waterspouts are commonly observed from just modest lines of cumulus congestus clouds, as occurred over Lake Champlain on 15 January 2009.
Arctic Sea Smoke or Steam Fog develops when very cold (arctic) air moves across relatively warm, open water. Strong upward fluxes of latent heat from the water surface result in water vapor quickly condensing as it is mixed and cooled with the adjacent cold air.
Since the air adjacent to the water surface is also convectively unstable, the arctic sea smoke or steam fog will be seen rising in turbulent plumes associated with shallow convective overturning of the very unstable air over the water (Lake Champlain in this case).
Upon further upward mixing, the fog will eventually evaporate and dissipate in the dry arctic air, on the order of 10 meters above the water surface. As such, arctic sea smoke is a relatively shallow phenomenon.
A "steam devil" is similar in nature to a waterspout in arctic air. However, we might differentiate between a steam devil and waterspout by whether or not the condensation funnel is deep and strong enough to be attached to a convective cloud above.
Deeper convective motions and vertical stretching extending from the water surface to the convective cloud base would generally result in a stronger, longer-lived feature (waterspout) as compared with a shallower, shorter-lived feature (steam devil). We might expect the vertical depth of a waterspout to be on the order of hundreds of meters, while the vertical extent of a steam devil is on the order of tens of meters.
Thanks to Jordan for keeping his weather eyes open over the big lake on Saturday.
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