Thursday, 11 February 2016

The Soutwest drought in the US isn't going anywhere

Even a Monster El Nino Can’t Beat the Southwest Drought


10 February, 2016
For those who follow weather, it’s a rather strange and disturbing story.
A powerful Pacific Ocean storm forms about 500 miles south of the Aleutian Islands. Heavily laden with rains, strong winds, and trailing a long squall line, the system takes aim at the US West Coast. It’s a burly beast of a thing. Pumped up by an enormous bleed of moisture rising off of one of the mightiest El Ninos ever seen. An instance of extreme Equatorial heat that’s been firing off since October.
Another Pacific Storm Deflected
(Another Pacific Storm is deflected northward by increasingly persistent high pressure systems as the US Southwest swelters under unseasonable warmth. GFS climate reanalysis by Climate Reanalyzer shows this disturbing weather pattern again and again in the February forecast. In short, it doesn’t look like the California Drought is going to end anytime soon. Image source: Climate Reanalyzer.)

The towering El Nino-fed storm clouds chug east, steaming along toward what appears to be an inexorable collision with California, Oregon, and Washington. But, at the last moment, the storm slams into a heavy pile of atmospheric heat. Warm air building over the US Southwest and nearby ocean zones has shoved the upper air steering current called the Jet Stream pole-ward. The great storm is sucked up into this atmospheric train, delivering its rains along an arc from Washington State on northward.
And so the seemingly impossible has happened. A powerful El Nino’s rains and snows — usually bound directly for California, Oregon and Washington — have been diverted by a new kind of atmospheric pattern associated with climate change.
El Nino’s Rains Gone or Just Taking a Break?

Ever since late January, strong ridges have tended to develop over Western North America. By February 4th, the National Weather Service (NWS) had begun to report on the pattern — describing  it as El Nino taking a 5-10 day break. But the ‘break’ had already begun to show up on January 26th — about ten days prior to the February 4 NWS announcement. And now, on February 10, we’ve seen two full weeks of warm, dry weather settling in over California and the US Southwest. Meanwhile, long range model forecasts indicate that the ‘break’ from El Nino conditions will continue through at least February 16h.

Upper 60s to upper 80s California and Arizona
(Temperatures in the upper 60s to upper 80s is predicted for a large sections of California and Arizona on Tuesday, February 16th. It’s the kind of hot, dry air that brings back memories of recent years when formations of strong, ridiculously resilient ridges pushed California into one of its worst drought episodes on record. Image source: Climate Reanalyzer.)

It’s all just terrible timing. First, California snow packs during December and January began to recover due to strong, El Nino associated, storm systems barreling in. However, now during what should be the peak of the Southwestern rainy season, we have what could be a month long pause in storms hitting the region. It’s as if the rainy season is being hollowed out. And not just any rainy season — a strong El Nino rainy season which should have been far, far rainier than most.

Last week, Climate Central and Peter Gleick — a climate expert at Pacific Institue — made the following warning:
seven days of sustained warmth could melt as much as 30 percent of California’s snowpack. The hot, dry weather is exactly what baked in exceptional drought in California over the past four years. Some signs indicate the heat is driven in large part by climate change, but the role of the ridiculously resilient ridge is still an area of active investigation.

Well, by tomorrow seven days will have come and gone. But the end to the anomalous warm, dry spell is still nowhere in sight.
California Drought Really Hasn’t Budged

Meanwhile, a four-year-long California drought appears to be making a strong run at year five. In fact, if you look at the US Drought Monitor, you’ll find that a large swath of the West is currently suffering under moderate to exceptional drought conditions.
West Still Suffering From Drought
(Severe Drought remains in place over the US West. El Nino appears to have lost at least some of its ability to deliver heavy rains as an intensifying regime of human-forced warming pushes typical weather patterns further and further off-kilter. All bad news for an area that has been suffering from one severe drought after another since the early 2000s. Image source: Drought Monitor.)

Quite frankly, it’s insane that we’re still seeing these conditions during a monster El Nino. These droughts should be rolling back as the storm track intensifies and hurls severe weather at the US West Coast. But that’s not what’s happening. At least not consistently. Instead, we keep getting these extreme ridge patterns in the Jet Stream over western North America. We keep getting these very warm, very dry spells of weather during the wet season. And now, we have California Snowpack melting away in February of all times.
A Ridge-Trough Pattern That’s All-Too Likely Related To A Human-Forced Warming of the Arctic

The fact that these weather patterns emerged after the warmest January and lowest sea ice extents on record for the Arctic is a point that should not be missed by weather and climate analysts. It appears that what we are seeing is yet more evidence that polar amplification is driving a consistent high amplitude bulge in the Jet Stream over Western North America together with severe periods of warmth, dryness and snowpack melt during Winter. The hot side of a dipole pattern that is also setting up more extreme storm potentials as cold air is driven out of the Arctic along a deep trough over the Eastern US, slams into a record hot Gulf Stream, and then sets off a series of atmospheric bombs along a storm track running all the way across the North Atlantic and into Western Europe. Yet more evidence that what happens in the Arctic doesn’t stay in the Arctic.

Links:
Hat Tip to DT Lange
Hat Tip to Andy in San Diego
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