Ever hear of a 'snownado?'

We’ve all heard about tornadoes and the devastation they can cause. In fact, more than 100 structures were damaged in the Houston, Texas, region Nov. 24 when at least one twister touched down. Several confirmed tornadoes were reported in Texas, with one in Mississippi. Wind gusts in the region were up to 115 miles per hour, according to the National Weather Service.

One phenomenon that is very rare is “snownados,” or “snow tornadoes.” This event is so unusual that fewer than a dozen photos have been taken. The snow tornadoes that have been captured will show a twisting white column that is spiralling across a frozen landscape. They are also known as snow devils, ice spouts, ice devils and snow spouts. Earlier this year, there were reports of snow tornadoes over Lake Michigan. Most of the known photos have been taken in Ontario, Canada.

Snow tornadoes can form over frozen lakes or other icy bodies of water and may be classified as a winter waterspout. A waterspout is a spinning column of air and water that forms over bodies of water. This will resemble a tornado over water. Waterspouts, including snow tornadoes, are usually very weak, but there have been instances of winter waterspouts reaching an intensity of EF1 that has resulted in some damage.

Snow devils, like dust devils, are a phenomenon that is closely linked to a snow tornado. These can occur on clear days as segments of the ground can heat up enough to warm a small layer near the surface. If there is light, powdery snow on the ground, the rising air from the warmer ground can lead to some minor air rotation. As a result, the snow can be lifted and provide the observer with a brief show of a spiralling column of snow.

Despite the snow tornado name, scientists say that the phenomenon is not driven by the same atmospheric mechanisms that produce the bigger tornadoes during the warmer seasons. A true tornado forms when warm, moist, unstable air interacts with strong vertical wind shear, often within a supercell thunderstorm. These conditions allow a rotating updraft, known as a mesocyclone, to tighten and extend to the ground.

Snowstorms, by contrast, will form in areas that are typically too cold, stable and lack the type of energy required to sustain such a rotating column. During a heavy snow event, the air is generally uniform in temperature, moisture and density, leaving little contrast to drive the violent ascent necessary for tornado production. For this reason, scientists do not classify any wintertime rotating vortices as true tornadoes, even though some may visually resemble or mimic them.

The closest the atmosphere ever comes to producing a true cold-season tornado occurs when a strong winter storm has sharp temperature contrasts. In rare situations, a tornado can develop within the warm sector of the storm while nearby areas experience snow. This can lead to misleading reports of a snow tornado, even though the tornado itself formed in a warmer air portion of the system that is separated from the snowfall.

Speaking of snowfall, the higher mountains have been receiving measurable snowfall since the weather pattern changed in November. Some of the ski resorts, such as Silver Mountain, are reporting snow depths of 9-14 inches. Lookout Pass has around a foot of snow at its summit. For the season to date, total snow has been around 20 to 60 inches in the higher mountains.

While some stations in the Spokane and Coeur d’Alene regions have reported some measurable snowfalls, very little, if any, snowfall has been measured in downtown Coeur d’Alene in November. However, 0.8 inches fell at the Spokane International Airport last week.

Moisture totals across the Inland Northwest were higher than average in Spokane as the airport received 2.61 inches, compared to the normal of about two inches. In Coeur d’Alene, rainfall totals were a little under the 3.07-inch normal, as 2.61 inches was reported. With the air masses from recent storms being too warm, snowfall averages in the lower elevations have been much below normal levels for November.

The overall weather pattern this month is still indicating a colder northwesterly flow from the Gulf of Alaska. Over the next several weeks, the long-range computer models are showing periods of rain and snow across the Inland Northwest with more snow in the mountains.

As we get closer to the new moon lunar phase Dec. 19, the long-range forecast models are still showing an increasing chance of colder and wetter conditions across the region. Assuming this pattern develops and continues through the end of the month, the chances for a White Christmas in the Spokane and Coeur d’Alene region are better than 50/50. Since 1895, there has been a White Christmas in Coeur d’Alene about 70% of the time, while the Spokane International Airport sees a White Christmas around 50% of the time.

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Contact Randy Mann at [email protected].