Severe Weather Outbreak Aardvark has brought death and destruction to parts of the eastern United States on Sunday and Monday. But he’s not finished. Tuesday will be another stormy day over the deep south, with more tornadoes almost a certainty. And there’s also action in the Pacific Ocean.
Aardvark’s rabid rampage through Arkansas and Missouri on Sunday left at least 16 people dead in the wake of tornadoes with winds up to 200 miles per hour. The normally docile animal continued his destructive behavior on Monday, causing at least 11 deaths and making rubble out of homes and businesses in Mississippi, Alabama, and Tennessee.
Aardvark is expected to throw another tantrum Tuesday, probably in many of the same places as Monday; and even Wednesday could see tornadoes in much of the south.
Precise forecasting of tornado locations more than a few minutes in advance is impossible. Instability occurs rapidly, especially during afternoons when daytime heating tips the atmosphere into a chaotic state. Aardvark contains all the ingredients needed for tornado production: a deep layer of warm, humid air near the surface; dry winds at higher levels; wind shear (a change of direction of the wind) with height. Daytime heating begins the process, creating updrafts which lead to thunderstorms. The twisting produced by the vertical wind shear can turn a dangerous thunderstorm into a deadly tornado.
El Niño Southern Oscillation (ENSO)
Signs continue to accumulate that an El Niño event, a warming of the tropical eastern Pacific Ocean, will take place this summer. Water temperatures in the central Pacific are now above normal for the first time since 2010. A cold upwelling is still in evidence right along the coast of South America, but the warm water is creeping eastward. This will be the first El Niño in four years, and, if it is a major one, the first such in 16 years.
What Does El Niño Do?
El Niño has wide-ranging effects including reduction in anchovy catches in Peru and reduced monsoon rain and a subsequent poor harvest in India. In the United States, El Niño are associated with mild hurricane seasons, wet weather in the southwest, and warm winters over the midwest and northeast. All of these would be welcome if they occur.
Southern California will experience a Santa Ana wind for most of this week. This phenomenon, known elsewhere as Chinook or Föhn, is a result of winds blowing down a mountain. As the air descends, it warms; since all the moisture has condensed and precipitated in the mountains. the air is also very dry. Los Angeles will have high temperatures in the 90s all week — about 20 degrees above normal — with humidities in the single digits and accompanying high fire danger.
Coastal Southern California normally has a marine climate, with cool winds blowing off the Pacific. Occasionally high pressure settles in to the north and drives winds down the slopes of the Coastal Range. Santa Ana winds are most common in the fall, but can occur in any season.
Santa Ana winds are exacerbated by the canyons on the west slopes of the Coastal Range. As air is squeezed into the canyons, the speed increases, occasionally to hurricane force, and the wind can rapidly spread fires.
Severe Weather, Looking Ahead
In the United States, March came in like a lion and went out the same way. April has been dominated by storms, culminating in Aardvark. Maybe in May all the animals will rest — but don’t bet on it. Though typical seasonal changes are taking place, the jet stream and polar vortex are still quite strong and displaced to the south.
Aardvark is an errant eddy that broke off from the core of the jet stream; these eddies, known as cutoff lows, move very slowly and produce persistent patterns of cold, heat, dry, and wet weather. They seem to be more common lately. Is it because of Global Warming? A pretty good possibility.
May is typically the climax of the tornado season in the U.S. We’re hoping for a mild May, but just in case, Decoded Science has selected a name for the next severe weather outbreak: Beaver.