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Intensifying Drought Shifts Toward Central U.S.

Last week saw a major increase in drought intensity in the Central U.S. as flash wildfires sparked across Oklahoma. Meanwhile, longer term drought trends remained strong even as the U.S. West Coast saw breaks in the dryness in the form of late winter precipitation.

(Drought expanded across the Central U.S. last week as precipitation deficits there increased. Image source: Drought Monitor.)

A return to severe to exceptional drought across the Western and Central U.S. was one of the hallmarks of the overall warm winter of 2017-2018. Historic drought, which had been suppressed by substantial rains during 2016-2017, appears to have returned — with threat of worsening conditions through spring, summer and fall.

In the Central U.S., the dry pattern reinforced this week which added to already serious conditions. During mid-week, Oklahoma saw the eruption of seven large brush fires as a result of both drought and strong winds sweeping across the plains states. Dry springs can result in fires for this region. However, the recent intensification of droughts brought on by human-caused climate change is spiking fire hazards from the Central U.S. through the West Coast and beyond.

(California snow pack totals remain well below average despite a recent increase in the number of storms affecting the state. Image source: CDEC.)

In California, snow packs are still running well below average, despite a recent wave of storms sweeping through the region. But it’s worth noting that though still much diminished from typical snow depth totals, the present range is now higher than the driest years — 2014-2015 and 1976-1977. So the situation isn’t looking quite so bad as it was a few weeks ago.

In addition, the blocking ridge that had dominated the West for much of the winter has mostly collapsed — allowing more rain and snow-bearing storms to cycle through. Some relatively intense precipitation is expected to fall over central and northern parts of the state later this this week. However, with widespread drought reasserting and with warmer than normal temperatures likely this spring, the increasingly drought-prone state is far from out of the woods.

(Temperatures have tended to remain above average across most of the U.S. this winter even as abnormally dry conditions impacted the Southwest. Image source: NOAA.)

Under human-caused climate change increasingly warm temperatures result in higher rates of evaporation from lakes and soils. This increases drought intensity for many locations around the world. In keeping with this longer-term trend, the winter of 2018 can still be characterized as both warmer and drier than normal for most of the U.S. But the overall drought pattern has shifted more toward the Central U.S. and away from the West Coast with the approach of spring.

 

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What’s the Real U.S. Weather Story for Fall and Winter of 2017-2018? Abnormally Warm, Abnormally Dry.

It seems that every time a snow storm or burst of cold weather roars out of a less stable and warming Arctic, the news media is all a-buzz. Perhaps this is due to the fact that these events are abnormal in their own right. Perhaps because they are more and more the extreme punctuations and back-blasts of a larger warming climate. Perhaps it is due to the fact that cold events are steadily becoming more of a nostalgic novelty even if, when they do arrive, they can come on with a fierce intensity.

 

(The overall trend for winter is one of warming. This despite the fact that more extreme Jet Stream patterns due to polar amplification can still produce bursts of cold weather. Note that regions furthest north are warming the fastest. Image source Climate Central.)

In the larger trend of warming and related climate change signaled extremes, the U.S. fall and winter of 2017-2018 is no exception.

Over the past 90 days, temperatures have been well above average across the western two-thirds of the country. Consistent blocking high pressure systems over the Pacific have generated both warmer and drier than normal conditions. In states like Wyoming, Nevada, Arizona, and Colorado, sections have experienced 5-6 C (9-11 F) above average temperatures for the entire three month period.

The Northeast, by comparison, which has seen the bulk of news coverage for recent briefer, less consistent, generally less intense cold events, has, at most, seen temperatures ranging 2-3 C (3.6 – 5.4 F) below average. In other words, the peak warm anomalies are beating out the peak cool anomalies by about 3 C — or 2 to 1 on the basis of intensity overall.

(Most of the U.S. has been much warmer and much drier than normal during the Fall and Winter of 2017-2018 with western heat and drought as the prominent feature. Image source: NOAA.)

Meanwhile, the high amplitude jet stream waves featuring cold air driven out of the Arctic by larger warm air invasions have been increasingly linked by scientific studies to human-caused climate change. These intense local cold snaps are now more often identified as a by-product of Arctic warming. Great floods of warm air invade northward, driving remnant cold air into the middle latitudes.

This bullying of cold by hot pushing mid-latitude temperatures into off-kilter extremes overlays a larger warming trend and is related to both sea ice loss and polar warming. But this particular climate change link — the fact that warm air in the Arctic is basically bullying the cold air out and is generating local, if intense, cold snaps — is presently under-reported in major broadcast weather media. Nor is the fact that daily record highs for the U.S. continue to greatly outpace daily record lows in the longer term trend being consistently highlighted.

(Though a handful of regions are experiencing cooler than 30 year average temperatures on February 7 of 2018, most of the globe today is much hotter than normal. Note that cold snaps, where they do occur appear to be concentrated in the Northern Hemisphere mid-latitudes. Also note that none of the major climate zones are experiencing below average temperatures even as much warmer than usual conditions are concentrated at the poles. These are all signatures of a warming world. Image source: Climate Reanalyzer.)

Despite a general overlooking of the context and causes for mid latitude weather extremes as identified by climate science, perhaps the most under-reported weather and climate change related story of the Winter of 2018 is the return of drought. Presently, more of the Continental U.S. is under drought conditions than not. And we are now experiencing, as a nation, the largest drought footprint in four years.

This is notable due to the fact that four years ago — 2014 — the U.S. west was experiencing one of the worst droughts in its history with California in the grips of a six year long extreme drought period. In other words, it would take both widespread and intense drought conditions to begin to compare to the 2014 drought situation either in extent or intensity.

With California receiving so much rain last winter (2016-2017) it is also notable how rapidly drought conditions have returned. California exited a drought emergency just a little more than a year ago. Now, a similar situation is again looming. Snow packs there are swiftly diminishing — and are presently just 27 percent of average for a normal February. Fire hazard never really went away following the record blazes of spring, summer, and fall of 2017. And concern over water reservoirs is again an issue on the minds of city and state emergency planners.

As is the case in climate change related impacts on Cape Town, South Africa’s own dwindling water supply half a world away, warming related concerns are a serious issue now for California and the U.S. West. And the fact that the most populous state in the U.S. may again be facing a similar crisis so soon after the 2012-2017 drought is a major piece of weather and climate news that everyone should be reporting. It’s part of a larger and ongoing climate crisis that a few flakes of snow or even a few severe cold snaps across the Northeast can’t really even hold a candle to. Especially when a jet stream riled by an Arctic forced to warm through human fossil fuel burning is the common thread running between both the eastern cold snaps and the western heat and drought.

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