reply to post by antar
Storms like these are a bit like the "Fire Triangle". In order to have Fire, you need 3 things:
Fuel, Heat, Oxygen. Remove any one of those and the fire goes out.
Storms are a lot like that. To have a strong thunder storm you need: moisture, instability and lift.
Moisture is pretty much self explanatory. The Gulf of Mexico helps provide that moisture sweeping in from there up north into the midwest and SE
Instability is the astmosphere's tendency to enhance or deter vertical motion. Unstable condistions, a lift of air will be warmer than the
surrounding air at that altitude. Because it is warmer, it is less dense and can rise more. This favors a storm's updrafts and downdrafts.
Lift provices the way for the air to rise, starting the thunderstorm process. Lift can be cold fronts, warm fronts, drylines and the flow up the
slopes of hills and mountains.
Once these storms move out over the ocean, they loose that lift. Again, like the fire triangle, you remove one of the ingredients, and the storm will
literally loose it's energy and go away.
So a line of thunderstorms along say a cold front, normally will go away once they head out over the ocean in many cases.
Weather fronts will push the storms in a west to east movement, however the storms themselves will flow along the front, from south west to north
east. If you watch the radar images from yesterday (and today), you can see that movement: IE the whole line of storms are being pushed to the east,
but the storm cells themselves are moving along the front from the SW to the NE.
Yesterday's storms are not unheard of. 1974 for example saw a very large outbreak too: 1974 Super
there were 30/40 F4/F5's and 148 tornadoes overall on that date.
Last year in April, for 3 days we had a super outbreak: 2011 Super
Here's a list of North American tornado outbreaks going back to 1671. Of course the further back you go, the spottier the information because of the
lack of weather record keeping:
North American Tornado Outbreaks
If you look, you'll see the greatest fatalities that ever happened was in 1925, but as you get closer to present day, the number of people killed
get's lower and lower. I think that's in part of weather predictions and people being alerted more in advanced.
If you look also, it seems that from 1980 on, there are larger numbers of tornadoes, but we have to be careful with those numbers, because reporting
tornadoes as you go back was harder to do. So it's better to look at 1980 onward to present day.
Becareful also on that number, as you need the word "confirmed", as it's possible for a single tornado to be reported several times, and mistakenly
adding to the count of actual tornadoes.
I suppose someone could take this data and make a graph, but will need to allow for errors in reporting, non-confirmation and of course the lack of
reporting in years past.
Hope people find the information interesting in any case.