2:20 PM | 2014 tornadoes near historic lows across the US thanks in large part to the persistent cold air outbreaks
While the middle of this week will likely bring the threat for tornadoes into the central part of the country, there is nothing but good news so far this year on the tornado front and a large part of the thanks can go to the persistent cold air outbreaks that we have experienced during the spring in much of the eastern half of the nation with the primary focus across the Great Lakes and Upper Midwest. In fact, the number of tornadoes reported to NOAA’s Storm Prediction Center (SPC) through April 20th is 109 (above) and this is one of the slowest starts in years to the tornado season - perhaps even as long as a century - which continues a downward trend that began a few years ago. The average number of tornadoes for this time of year is 413 based on the period from 2005-2013. The yearly nationwide tornado totals for the last two years (943 in 2013, 1119 in 2012) were the lowest annual amounts of any of the past ten years according to NOAA’s SPC. One other favorable bit of news on the tornado front is the fact that we have not had an EF-3 or stronger tornado in the last 152 days which is the 4th longest span in the past 60 years without that type of strong tornado (below).
The overriding reason for the low number of tornadoes so far this year - as well as for much of last spring - has to do with the fact that the persistent cold weather pattern in much of the central and eastern U.S. has greatly reduced the chance for severe weather by inhibiting moisture-laden warm air from the Gulf of Mexico to flow northward into the southern U.S. This is an important, and generally necessary, ingredient for severe weather and the generation of tornadoes. Indeed, this same persistent cold weather pattern has contributed to the record high ice cover extent across the Great Lakes – still continuing at this late date – and more cold air masses are in sight for this region of the country through at least next week and the beginning of May.