Thursday, 22 June 2017

Extreme weather in the United States

U.S. Climate of Troubles: Record Heat Out West, Severe Floods in the East


21 June, 2017
Yesterday a record heatwave affecting 40 million people cracked pavement, grounded flights, threatened power grids and risked serious injuries across the Southwestern U.S. Meanwhile, today, a heavily moisture laden tropical storm Cindy is threatening to dump 10 to 15 inches or more of rain on parts of the U.S. Southeast. A pair of opposite weather extremes of the kind we’ve come to expect more and more of in a world that’s warmed by about 1.2 C above 1880s averages.

(Very extreme weather conditions settled over the U.S. on June 20. Today, Cindy is expected to bring extraordinary rainfall totals to the U.S. Gulf Coast. Video source: ClimateState.)

Record-Shattering Western Heat

Yesterday, the mercury struck a scorching 127 degrees F in Death Valley California — the hottest June 20th ever recorded for that heat-blasted lowland. Meanwhile, Death Valley-like heat spilled out over a large swath of the southwest. Phoenix fell just shy of its daily record as temperatures struck 119 F. And Las Vegas tied its all-time record of 117 F (which was set just four years ago on June 30th). Needles, Daggett and Barstow in California joined Kingman in Arizona and Desert Rock in Nevada to also break previous heat records as temperatures soared to between 111 and 115 F across these cities and towns.
(Record heat hammered the U.S. West on Tuesday spiking fire hazards, grounding planes, causing power outages and increasing the risk of heat injury. Image source: National Weather Service.)

All these severe high temperatures took a serious toll as both cities and citizens fell under blast-furnace-like conditions. In Phoenix, 43 flights were grounded. Aircraft could not generate enough lift for a safe take-off in the thin, low-density hot air. Total number flights grounded since Monday now tops 50 for the city — with more expected Wednesday when temperatures are expected to hit 118 F.
As flights were grounded in Phoenix, fires began to spark across the Southwest. Several fires ignited in Southern California including a large 950 acre blaze near Big Bear. In Utah,hundreds of people were forced to evacuate a ski town when a weed-killing torch ignited a swiftly spreading fire. And in southwest Arizona, a wildfire burned 8 structures as more than 100 firefighters rushed to contain the blaze. Firefighters across the southwest struggled against some of the most difficult conditions imaginable — extreme heat, blustery southerly winds, and rapidly-drying vegetation.

Record heat also overwhelmed grids when customers cranked up air conditioning and high temperatures put a major strain on power lines and transformers. With California temperatures climbing to historic levels yesterday, power outages were reported across Central Valley and on into the Bay area. Extreme warming of road surfaces caused highways to buckle even as hospitals prepared for a surge of various heat-related injuries from burns, to heat exhaustion, to heat stroke.

(Recent warming of ocean surfaces to well above average ranges off the U.S. West Coast have likely boosted the development of the recent western heatwave. Ocean surface warming is a signature condition of human-caused climate change. Image source: Earth Nullschool.)

A strong high pressure system and a large associated ridge aided by abnormally warm waters off the U.S. West Coast are the primary regional causes of the most recent heatwave. The pool of warm water in the Northeast Pacific — somewhat reminiscent of the Hot Blob that formed in the nearby ocean zones during 2014 and 2015 — appears to be boosting the development of upper level ridges and related surface heat over the region as temperatures climb to 10 to 25 F or more above normal for many locations. Despite recent record winter and spring rainfall for parts of the region, this new heatwave is starting to again advance drought conditions across the Southwest. Yet another hard shift in weather extremes from wet and cool to dry and hot that can likely be linked to climate change.
Cindy Ushers in Severe Flooding across the Gulf Coast

While the west scorches under extreme heat, the weather threat to the U.S. Southeast comes in the form of severe flooding. In the Gulf of Mexico, a sprawling Tropical Storm Cindy is interacting with a stalled frontal system to spike moisture levels in the atmosphere above the U.S. Gulf Coast. Already, between 3 and 9 inches of rain have fallen over parts of Louisiana, Mississippi, Florida and Alabama. But the slow-moving, heavy rain bearing Cindy is poised to dump still more.
(24 hour rainfall totals show that heavy precipitation in the range of 3 to 9 inches have already fallen across the Gulf Coast. Cindy is expected to bring even more over the coming days. Image source: NOAA.)

According to NOAA QPC predictions for the next week, as much as 8.5 additional inches of rainfall could impact already-flooded parts of SE Louisiana. And when all is said and done, the system is forecast to drop between 10 and 15 inches or more of rainfall over parts of the area. The storm is not presently expected to rival last year’s August rain event which dumped up to 30 inches over the same region. Of course, with climate change boosting rainfall potentials by warming the Gulf of Mexico and spiking atmospheric moisture and instability, the unexpected can certainly happen. Let’s just hope that’s not the case with Cindy. But 10-15 inch rainfall totals are certainly disruptive enough. And with some streets in New Orleans already seeing 2-3 feet of flooding as more storms rush in from the Gulf, this event is certainly far from finished.

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Hat tip to Suzanne
Hat tip to Greg
Hat tip to Tigertown

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