Severe Season Waking Up
Similarly to 2013, the start of 2014 has been off to a relatively slow start in terms of severe thunderstorms and tornadoes. Through the end of March, there were only 70 tornadoes reported across the U.S. That’s the lowest number in recent years, looking back to 2005. The next lowest count was 79 through March 31st in 2010. Last year featured 151, but the 2005-2013 average is 243. That number is skewed high, because some early season tornado outbreaks can be particularly severe with over 50-100+ tornadoes, while other seasons start slow and do not see an up-tick in activity until later in spring.
Climatologically speaking, the severe season really begins to ramp up in April. This is the month that sees the fastest increase in average severe activity per day, before things level out for a relative peak by late spring and early summer.
Many of the most significant tornado outbreaks have occurred in April. Simply explained, this literally has to do with the change of seasons. While cold air to the north may linger across the northern states, an increasing sun angle and a developing sub-tropical ridge result in sharply warming temperatures across the South. All it takes is one storm to develop across the Plains/Midwest and tap into these chasing air-masses.
As we move into April 2nd and 3rd of 2014, there is increasing confidence in a severe outbreak across the center of the country. While there is still some uncertainty with just how significant the outbreak could be, it’s a sign of things to come over the next few weeks. Despite stubborn troughiness and
below average temperatures across the Great Lakes, a warm, moist flow from the Gulf will inevitably lead to more severe outbreaks.
What can we expect later in April?
It looks like the overall pattern from April 4-14 will see minimal severe activity overall. It’s around mid-month that I think the season could really kick into gear. Although it’s still very early speculation, my focus shifts toward a ridge along the West Coast. A pattern with a trough in the East and a ridge in the West does not sound very exciting for severe prospects in the Plains and Midwest. However, it’s the eventual breakdown of such a pattern that concerns me. As the western Ridge advances east, eventually the trough that was over the Pacific advances into the West and allows for shortwave disturbances to dig east of the Rockies and spawn severe weather in the Plains. Some analogs, such as April 1996, featured a significant severe outbreak in mid to late April despite eastern troughing to start the month. The longer range GFS and European ensembles are showing this by mid-April of this year.
Stay tuned for more updates and I look forward to providing extensive severe weather coverage starting next week.
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