On Wednesday, June 29, 2005, a weak tornado briefly touched down in southern Newaygo County. The tornado touched down in an open field in the vicinity of 120th and Spruce roads, about six miles southeast of the community of Newaygo, at around 5:20 PM. The tornado was on the ground for approximately five minutes and several eyewitnesses were able to confirm the tornado touchdown. The tornado caused no structural damage and was rated at F0 (wind between 40 and 72 MPH) on the Fujita scale. The tornado was unusual in that it occurred with a relatively innocuous towering cumulus cloud.
This write-up will briefly review the development and dissipation of the Newaygo County tornado. The tornado that developed in Newaygo County on June 29th is what is referred to as a landspout tornado. Landspouts are named as such because of their resemblance to the rope-like appearance associated with waterspouts (Figure 1). Landspouts are particularly common in the High Plains and along Front Range of the Rocky Mountains, but can occur anywhere that the appropriate ingredients come together.
The formation mechanism for landspouts is very different from that of the most destructive tornadoes. Landspouts develop as a thunderstorm, or even a towering cumulus cloud, rapidly develops above a surface boundary such as a lake breeze or wind shift. Surface boundaries such as lake breezes have small scale circulations along their long axis that can play an important role in the development of landspout tornadoes. To help visualize these circulations imagine two hoses facing each where the water flowing out of the hoses represents the wind on either side of a wind shift. If you were to set the hoses several feet apart and offset just a bit (i.e., not flowing directly into each other) you would see small circulations develop as the two streams of water which are flowing in opposite directions interact with each other. You could also mimic this effect if you lit a candle or incense and then moved your hand slowly downward alongside the smoke that is rising from the incense. As two air streams on opposite sides of a front or wind shift interact small eddies or circulations form along the interface of the two airstreams.
These surface circulations are critical to the development of landspout tornadoes. As a thunderstorm, or towering cumulus cloud, rapidly develops above one of these circulations the developing storm is able to stretch the low level circulation into a weak short-lived tornado on rare occasions. The process of tightening and intensifying the circulation below the storm’s updraft can be readily visualized. If you watch an ice skater spinning with his/her arms out they will rotate slowly. However, when they raise their arms above their head to make the axis of rotation more narrow they will spin much more quickly. Something very similar occurs when a landspout develops. In the case of a landspout as an innocuous low-level circulation is stretched vertically into the developing storm's updraft, the axis of rotation contracts substantially and correspondingly begins to rotate more rapidly.
Landspouts are most likely to occur when the following conditions are met:
Typically land spouts develop very quickly after updraft initiation. They are extremely difficult to warn for as they often develop from innocuous towering cumulus and can occur very rapidly after the initiation of the updraft.
Even at close ranges there is very little circulation evident in the towering cumulus or thunderstorm, even with the most powerful and sensitive of radars (such as the NWS WSR-88D), as the landspout tornado is not associated with a rotating storm, but instead is stretched from the surface to cloud base.
With these basic concepts in mind let’s look at the evolution of the Newaygo County landspout. The visible satellite imagery (Figure 2) clearly defines the lake breeze boundary by the line of cumulus clouds that are developing along its axis. To the west of the lake breeze there are no cumulus clouds as stable marine air advected off of Lake Michigan prevents low level cloud formation. Note that the lake breeze front stretches through south central Newaygo County.
Figure 3 is a radar image from the NWS Grand Rapids WSR-88D, taken at 5:13 PM. The lake breeze is clearly visible stretching from southern Newaygo County through western Kent County and is highlighted by the yellow line in the image. The image also indicates the developing updraft (inside the red circle). It is important to note that the western edge of this updraft is located directly over the lake breeze boundary.
The radar image at 517 PM (Figure 4) shows the developing storm still located on the lake breeze boundary.
The landspout tornado is on the ground by 520 PM and a radar image at 522 PM (Figure 5) shows further intensification of the developing storm. Note there are stronger cells to the south across Kent County at this time. The updraft with the Newaygo County cell is still so shallow (even with a tornado on the ground) that it is not yet producing lightning.
By 526 PM the landspout has dissipated as cool outflow from rain-cooled air beneath the developing storm undercuts the landspout.
In the radar image at 526 PM (Figure 6) the outflow begins to appear as a ‘bulge’ in the reflectivity on the west side of the storm. Even though the storm continues to strengthen the landspout tornado has dissipated. By 535 PM the storm is finally generating cloud-to-ground lightning and eventually it produces three-quarter inch hail in southern Newaygo County.
The radar image at 547 PM (Figure 7) shows a now mature thunderstorm still located above the lake breeze. The cool outflow is more evident at this time as the rain-cooled air has completely undercut the storm.
In many ways this was a classic example of landspout development with a rapidly developing updraft co-located with a low level circulation along a nearly stationary boundary. As is typically the case with landspout tornadoes the tornado was weak and short-lived. However, all tornadoes are dangerous to those in the vicinity and fortunately this tornado remained in open country for its entire life-cycle.