Nasty weather on the way, is El Nino at work?
As expected, a fall season featuring El Niño has been active in the Southern United States. So far, record breaking rain events have grabbed headlines, but severe storms may be the next act.
One week after damaging winds and white-out wintry weather in the Midwest, a similar set up shifts farther south—minus the white stuff.
Forecast models indicate that a significant trough will soon slice through the southern third of the United States. East of the trough, where cool air displaces warm, is where forecasters look to as a potential alarm for severe weather. The deeper the trough, the louder the siren; and this one is ringing.
A strong mid-latitude cyclone will develop and mature across Texas on Monday. In Oklahoma, Texas, Arkansas and Louisiana, ample moisture will pool with a moisture field almost 200% of average. A strong low level southerly jet will veer to a powerful westerly flow aloft, creating the wind shear necessary for rotating storms. Instability won’t be overly impressive, but look no further than Halloween to find an example of nasty storms without ideal instability.
Precipitation may become scattered as early as Monday. The storm system itself will be slow to move with an accompanying cold front not kicking through the Central Gulf Coast until Wednesday. Thus, there will be an extended window for heavy rain and this setup certainly needs monitored for severe weather—all modes, including tornadoes, are on the table right now.
Unnerving maybe, but the “T-word” should not be surprising to Central Gulf Coast residents during the fall season.
Certainly, the spring surge of tropical moisture clashing with winter leftovers in the Midwest and Gulf South makes March to May peak tornado season. Not to be underestimated though, is the arrival of cold air displacing lingering summer humidity southward. Indeed, October to December offers a fair smattering of spin ups as well. The Baton Rouge area may recall a Christmas Day outbreak in 2012 or the Amite tornado on December 23, 2014—the latter of which was the strongest to occur in the WBRZ forecast area over the last 5 years.
Over the last 30 years, there have been 160 confirmed tornadoes in the WBRZ forecast area resulting in 5 deaths, 149 injuries and $32.5 million in damage.
40% of those tornadoes unsurprisingly occurred during the “textbook” severe weather season of March to May. However, 27% of the twisters in that 30-year period happened in the months of October, November and December. Combined, that accounts for 96 of the 160 events. The remaining 33% happened in no discernable cluster over the other 6 months of the year.
Perhaps the most telling stat comes from a closer look at tornado strength in those 20 years. The fall season produced barely fewer (35) EF1 or stronger tornadoes than the spring season (40). No tornado at any time of year should be taken lightly and the number proves that destructive twisters aren’t just reserved for spring.
A deeper look at tornado statistics for the Alabama, Louisiana and Mississippi confirms that severe weather in the fall season is quite common—but perhaps even more so with El Niño in full swing.
Over the last 25 years, times of warmer ocean temperatures in the Southwestern Pacific, the root cause of El Niño, have translated into more active fall tornado seasons for the Central Gulf Coast. This is due to a more active low-level jet stream, the river of air aloft that controls weather patterns.
The trend is particularly evident in Louisiana, where a deep and rich moisture field is more prevalent later into the fall season.
During the 2002 El Niño autumn, a November 11 F3 tornado killed 7 people and injured more than 40 in Townley, Alabama. On that same day, another F3 hurt 55 folks in Artesia, Mississippi. The 1997 El Niño fall found a strong F2 twister in Covington, Louisiana injuring 47.
Despite those notable fall tornadoes over the last 25 years, fortunately, there are no trends to suggest the chances of an EF2+ tornado increase during an El Niño autumn. Actually, a greater percentage of strong tornadoes since 1989 have occurred in non El Niño years along the Central Gulf Coast.
And not all El Niño autumns mean an active tornado season for Alabama, Louisiana and Mississippi. There have been relentless years like 2002 and 2004 where tornado counts were chart topping. In other instances, 1991, 1994 and 1997—which is considered by many as the landmark El Niño event—the tornado count was considerably low.
Is the fall tornado season likely to be more active along the Central Gulf Coast during an El Niño autumn? Yes. Does this come to fruition in every instance? No. Will this year be one of the more active fall tornado seasons? Only time will tell.
Away from the trends and back to the present—the latest threat is real. Experts at the Storm Prediction Center have tapped into their experimental 4+ day outlook to underscore the severe weather potential. Residents from Dallas to Houston, Baton Rouge to Shreveport should note the possibility of more heavy rain, damaging wind and a tornado.
Stay connected with our team as we monitor the latest forecast.
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