This time of year can bring tornadoes, even ‘thundersnow’

With the exception of maybe the three months of hot, dry summer, you can’t really say that the weather is boring in this part of the country. Wild weather over the past couple of weeks has proven that Mother Nature can throw this region all sorts of curve balls. On Jan. 10, a tornado struck the Vancouver area in southwest Washington. Before that, Walla Walla endured a ferocious wind storm with winds gusting to near 80 mph resulting in more than $2 million worth of damage. Most recently, the Palouse got slammed again with snow, blowing snow and even “thundersnow.” Granted, the Panhandle was not caught in the midst of these latest storms, but their occurrence just goes to prove that no place is immune from extreme weather.

The Vancouver tornado was an unusual event, not only because it occurred in a state that only averages two tornadoes per year (Idaho averages only three), but also because it occurred during the winter. The tornado struck around noon, with multiple touchdowns over the course of about 30 minutes, and a damage path of nearly 10 miles. On a damage scale of EF-1 to EF-5, this tornado ranked a mere EF-1, considered weak. For comparison, the tornado that wiped out the town of Greensburg, Kan., last May, and the one that flattened the town of Moore, Okla., in 1999 were given the highest rating, an EF-5. That being said, the Vancouver tornado knocked down more than 200 trees, damaged 30 to 40 homes, snapped off 19 power poles, tipped over a semi trailer, and then some. Winds were estimated to be between 90 to 110 mph.

Farther east in Walla Walla, strong winds not associated with any tornado or even thunderstorm caused widespread damage and knocked out power to a quarter of the town. The cause of the winds was a powerful low pressure system offshore which actually resulted in a record breaking low (mean sea level) barometric pressure reading of 28.93 inches of mercury at the Walla Walla airport. What was also unusual about the strongest winds was they were not confined to the higher elevations around the city. Normally, wind speeds increase with height due to a reduction in friction from the ground. This is definitely noticeable at ski resorts where sometimes chair lifts have to be shut down due to the gusty winds higher up in the mountains. In the case of the Walla Walla storm, however, wind gusts up to 80 mph were recorded at the airport elevation of 1,204 feet. Only slightly stronger, were wind gusts of 85 mph reported in Joseph, Ore., elevation of 3,984 feet and gusts of 80 mph reported at a weather station nine miles west of Tollgate, Ore., elevation of 3,581 feet. Meteorologists at the Pendleton National Weather Service office believe that local terrain effects (i.e. winds accelerating down a mountainside) played a large part in creating such strong winds at the lower elevations.

Finally, I received an e-mail at from a person who could not believe his eyes when he saw a lightning flash while driving through nearly blinding snow south of Pullman off highway 195 this past week. He wasn’t seeing things, and there is a term for it – “thundersnow.” It is essentially a thunderstorm with snow instead of rain. It is not a common occurrence, and like a thunderstorm which can produce heavy rains in a short period of time, this particular thundersnow event produced 2 inches of snow in less than one hour. Winds created whiteout conditions and knocked out power to more than 3,000 people in Moscow. Thundersnow events are usually quite localized, producing heavy snow bursts, but only across a limited area.