Saturday, 24 February 2018

Major flooding in central U.S

Climate Change Driven Record Atmospheric Moisture Produces Major Flooding in Central U.S.

23 February, 2018

Ten inches. That’s how much rain has fallen over parts of the Central U.S. over the past week. Five-to-ten inches more. That’s how much additional rain could again fall across the same region during the next seven days according to NOAA’s forecast (see below image).

(The Central U.S. is already experiencing severe flooding. But record atmospheric moisture levels driven by extreme ocean warming is setting up conditions for even more intense weather. Image source: NOAA.)
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Warnings of potentially life-threatening flooding were issued today from Michigan to the Ohio Valley and on through a large swath stretching from Texas into Arkansas as severe rainfall again inundated the Central U.S.

A massive double-barrel high pressure system sitting off the U.S. East Coast generated strong south-to-north winds running over sea surfaces in the Gulf of Mexico ranging from 1 to 5 C warmer than average. These winds reaped the waters of a much larger than normal load of water vapor and then pumped it over the Central U.S. The result was record atmospheric moisture levels running over the region producing significant and abnormally intense rain storms. Now, many areas are under flood warnings with moderate-to-major flooding expected.

(Much warmer than normal sea surfaces over the Gulf of Mexico resulted in increased atmospheric moisture loading. Image source: Earth Nullschool.)

1-5 C warmer than normal ocean surfaces, as we see in the Gulf of Mexico today, is an extraordinary anomaly. In the past, 2 C warmer than normal readings would have been considered significant. But with human-caused climate change, sea surface temperature anomalies have tended to become more and more extreme.
Though warmer than normal Gulf of Mexico waters are contributing to the presently severe precipitation now falling over the Central U.S., they are not the only waters seeing such high temperatures. In fact, the global ocean is now much warmer than it was in the past and, from region-to-region, produces abnormally high surface temperatures with increasing regularity. These warmer waters have pumped more moisture into the Earth’s atmosphere which has led to an increase in the number of extreme rainfall events both in the U.S. and across the globe. A signal of human forced climate change.


(Large east coast high pressure systems, seen in right of frame as two clockwise swirls, hit a record intensity this week beneath an unusually intense ridge in the Jet Stream. The highs also served to pump that intense Gulf moisture into the Central U.S. Image source: Earth Nullschool.)

The large high pressure system driving such a significant moisture flow over the Central U.S. today is also climate change related. Earlier this week, the high hit a record intensity — spurring a never-before-seen spate of record warm temperatures across the U.S. northeast. The high, in its turn was fueled by a warming-driven polar vortex collapse in the Arcticwhich generated the intense ridge pattern that allowed it to bloom and sprawl.

What we are seeing, therefore, is a kind of climate change related synergy between severe polar warming and more intense ridge and trough patterns in the middle latitudes. Add in the factor of warmer sea surfaces and this changed atmospheric circulation is enabled to more efficiently tap related higher atmospheric moisture levels to fuel the more intense storms we’re seeing today.

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