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

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 Arctic which 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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Under the Arctic Dome — Brutish High Pressure System is Wrecking the Already Thinned Sea Ice

There’s a real atmospheric brute towering over the Arctic’s Beaufort Sea at this time. A high pressure system that would put shame to most other anti-cyclonic phenomena that bear the name. It is sending out a broad, clockwise pattern of winds. It is pulling up warm air from the Pacific to invade the Bering, Chukchi, East Siberian and Laptev Seas. And its torquing motion is shattering the already considerably thinned ice beneath it.

(A powerful high pressure system over the Beaufort Sea is predicted to further strengthen by late April 15. Image source: Earth Nullschool.)

Clocking in at 1046 mb of pressure, it makes typically strong 1030 mb high pressure systems seem weak by comparison. Over the next day it is expected to strengthen still — hitting 1048 mb by late April 15th (coming very close to an extraordinary 1050 mb system).

Shattered Sea Ice

This powerful and strengthening system has already been in place for about two weeks — slowly gaining momentum as its circulation has moved in mirror to the waters of the Beaufort Gyre that swirl beneath it. Masked only by a veil of sea ice considerably thinned by human-forced climate change, the waters of the Beaufort are now breaking through. Streaks of dark blue on white in an early break-up enabled both by a terrible Arctic warming and by this powerful spring weather system.

(Side-by-side images of Beaufort sea ice from April 4 [left frame] to April 13 [right frame]. Note the considerable and rapid advance of fracturing in a relatively short period. For reference, bottom edge of frame in both images is 500 miles. Image source: LANCE MODIS.)

Warm Storms

On the Siberian side of the Arctic, this massive high pressure dome is drawing in warm winds from the Pacific Ocean. Gust by gust and front by front, they come in the form of squalls that deliver above freezing temperatures and rains that blanket this thawing section of the Arctic. On Thursday, April 13, these warm winds had driven northward over 2,500 miles of Pacific waters to be drawn into storms that unleashed their fury — driving rains and gales through the already dispersed ice in the Bering Sea and shattering ice floes through the Chukchi. Today, April 14, these winds and rains drove northward to assault the ice of the East Siberian and Laptev seas.

(On April 13, above freezing temperatures, rains, and gale force winds ripped through the sea ice near Wrangle Island in the Chukchi Sea. Image source: Earth Nullschool.)

A Great Atmospheric Stack Drawing Heat into the Arctic

In the past, meteorologists like Stu Ostro envisioned that climate change would tend to produce towering high pressure systems — featuring increasingly strong storms roaring about their fierce outer boundaries. And the massive high lurking over the Arctic at this time is a good example of Ostro’s predictions coming to light in a region that is very sensitive to human-forced warming.

This great atmospheric stack appears to have had a considerable impact on the ice already — helping to push extent measures back into record low ranges by accelerating the melt trend. But these impacts are likely to spike over the coming week as this powerful high expected to remain in place through the next five days — continuing to draw warm air into the region.

(Global Forecast System models predict extreme warming over the Arctic Ocean throughout the next week resulting from the influence of a powerful high pressure system and very strong associated ridge in the Jet Stream. Image source: NCEP Global Forecast System Reanalysis.)

GFS model runs indicate that average temperatures over the Arctic Ocean region will hit a peak as high as 4 degrees Celsius above average by late next week. Meanwhile, the warmest zones are expected to be as much as 18-20 degrees Celsius above average. Such abnormal warmth at this time of year, if it emerges, will put a considerable damper on a freeze that should now be continuing in the High Arctic even as edge melt ramps up with the progression of spring.

This is particularly concerning due to the fact that temperature anomalies in the Arctic tend to fall off during spring and summer. In other words, such a powerful warming trend for the Arctic Ocean would be bad enough during winter — but it is an even more unusual event for spring. An ominous start to a melt season that could produce far-reaching regional and global consequences.

Links:

Earth Nullschool

LANCE MODIS

NCEP Global Forecast System Reanalysis

Stu Ostro

Climate Reanalyzer

Hat tip to Colorado Bob

Hat tip to Andy in San Diego

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