Droughts
can be quite nasty with it comes to rainfall.
However, droughts can be a good thing when it comes to severe
weather. The U.S. is currently
experiencing such a drought for tornadoes.
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| The monthly number of tornadoes for 2013 compared to the 1981-2010 average. Click on the image for a larger version. Image Credit: Climate Central. |
The
year started off looking above normal, but that quickly turned in
February. Significantly fewer tornadoes
were observed in March and April. May is
normally the peak of tornado season for much of the country. The drought has continued and will likely
continue into the middle of May. It is
hard to say if it will continue beyond that, but it is likely.
The
second busiest year on record for tornadoes was 2011. The weather pattern that year was coming off
of a strong La Nina. The map below shows
the path for many of the tornadoes nationwide as well as the intensity. Compare that with 2012 which like this year
showed a low number of tornadoes.
 |
| The top chart shows all of the observed tornadoes for 2011. The bottom chart is for 2012. Click on either map for a larger version. Image Credit: NOAA/SPC. |
A
major rainfall drought hit much of the tornado belt in 2012. The lack of moisture yielded fewer
thunderstorms which are required for tornado development. While the rainfall drought has continued this
year it has eased for much of the tornado belt.
This year it has been the unseasonably cool spring that has reduced tornado
development. The thunderstorms needed to
produce tornadoes need heat and moisture.
South
Carolina is not in the tornado belt of the central U.S., but there has been a
tornado drought here as well. The chart
below shows that only one tornado has been observed so far and that was near
Ridgeway in Fairfield County. The peak
month for tornadoes in this state is May.
There is a secondary peak in August associated with tropical activity.
 |
| The tornado drought in South Carolina for January-April, 2013. Click on the image for a larger version. Image Credit: Climate Central. |
While
there is a tornado drought in progress, it is always best to be prepared for
any severe weather. The National Weather
Service has published an excellent guide explaining much of the severe weather
for South Carolina. There is a great
deal of useful information in this short guide.
What’s more you can get it online here.
In
2011 there was talk of climate change affecting tornadoes because of the large
number. How can we reconcile the current
drought of tornadoes which is the lowest in about 60 years?
Tornadoes
are weather events. Global warming is
changing the climate and hence weather patterns. This may at times impact the production of
tornadoes. However, the scientific
literature does not answer how climate change will alter the number or
placement of tornadoes. It is reasonable
to expect that as the earth warms tornadoes may expand their range northward in
Canada. Last year was a very busy year
for tornadoes in central Canada.
It
is less clear how this will play out in the central U.S. Tornadoes are complicated beasts, affected
not only by moisture and temperature but also by wind shear and other factors.
So far, there’s simply not enough information to say anything definitive about
the future of tornadoes under global warming.
