Average temperatures across the contiguous U.S. for each year since 1895. (Image credit: NOAA/NCEI)This is a re-post from Yale Climate Connections by Bob Henson
One of the hottest years in U.S. history, 2020 was besieged by a record number of billion-dollar disasters, led by two of the most dangerous phenomena with links to climate change: wildfires and hurricanes. In its initial U.S. climate summary for 2020, NOAA catalogued a year that fell firmly in line with expectations for a human-warmed climate.
The average temperature last year for the contiguous U.S., 54.37 degrees Fahrenheit, was the fifth warmest in 126 years of recordkeeping, NOAA reported. All five of the warmest years on record – 2012, 2016, 2017, 2015, and 2020 – have occurred in the past decade. The 10 coldest years were all before 1980.
Based on preliminary data from NOAA compiled by independent meteorologist Guy Walton, the U.S. had more than twice as many daily record highs (33,698) as lows (15,698). A 2009 paper by Walton and colleagues predicted that the typical ratio could reach 20-to-1 by mid-century and 50-to-1 by late in the century.
The average U.S. temperature in 2020 is more than 2°F above the 20th-century average (see image below).
Average temperatures across the contiguous U.S. for each year since 1895. (Image credit: NOAA/NCEI)
When nationally averaged, the 30.28″ of contiguous-U.S. precipitation in 2020 was close to the long-term norm, but that innocuous-sounding statistic obscures some big shifts and a pronounced west/east split.
Back in 2018 and 2019, large parts of the central and eastern U.S. were inundated by relentless rains, leading to the wettest 12-month spans in U.S. history. During 2020, as the Pacific swung into a potent La Niña event, the nation finally began to dry out. Even so, 2020 was one of the 10 wettest years on record for most of the southeastern U.S., and the second wettest for North Carolina.
Some parts of western North Carolina and Virginia had their wettest year on record in 2020, including:
Rocky Mount, VA: 77.22″ (old record 75.46″ in 2018; records begin in 1894)
Pulaski, VA: 70.06″ (old record 56.54″ in 2018; records begin in 1920)
Roanoke, VA: 62.65″ (old record 62.45″ in 2018; records begin in 1912)
Roanoke had its hottest and also wettest year on record – an uncommon juxtaposition, as wet summers tend to be on the cooler side.
Rankings of average precipitation for each contiguous U.S. state in records going back to 1895. Darker green colors indicate wetter conditions; darker brown denotes drier conditions. (Image credit: NOAA/NCEI)
Meanwhile, 2020 was the driest year on record in Nevada and Utah, thanks in large part to anemic summer rains from the North American Monsoon. It was among the five driest years on record across a huge area from California east to Wyoming, Colorado, and New Mexico. The San Francisco Bay and Reno/Tahoe areas both had their second driest calendar year on record.
Cities that had their driest year on record in 2020 included:
Tucson, AZ: 4.17″ (old record 5.07″ in 1924; records begin in 1894)
Flagstaff, AZ: 9.59″ (old record 9.90″ in 1942; records begin in 1898)
It was also Tucson’s second hottest year on record.
Even after adjusting for inflation, the U.S. had more billion-dollar disasters in 2020 – a total of 22 – than in any year in NOAA records going back to 1980. The total was more than three times the average annual tally of seven such disasters, and it far exceeded the previous record of 16 from 2017.
The year’s billion-dollar events included 13 severe storm events, seven tropical cyclones, one series of wildfires, and one major drought. Collectively, the costliest phenomenon was the string of 11 hurricane and tropical storm landfalls – the most in 170 years of recordkeeping – that affected the entire Gulf and Atlantic coast from Texas to Maine. Those that made the billion-dollar damage list were:
#1: Hurricane Laura ($19 billion, 42 deaths)
#4: Hurricane Sally ($7.3 billion, 5 deaths)
#5: Hurricane Isaias ($4.8 billion, 16 deaths)
#8: Hurricane Zeta ($3.5 billion, 6 deaths)
#10: Hurricane Delta ($2.9 billion, 5 deaths)
#15: Tropical Storm Eta ($1.5 billion, 12 deaths)
#21: Hurricane Hanna ($1.1 billion, no deaths)
Every single mile of the U.S. Atlantic coast was under a watch or warning related to tropical cyclones at some point in 2020. (Image credit: National Weather Service/Corpus Christi)
Close behind Laura, at #2 on the billion-dollar list, was the swarm of western wildfires from August to December that took advantage of “hot drought” conditions (a phenomenon strongly linked to climate change) over vast areas. Together, the fires caused $16.5 billion in damage and took 46 lives.
The most dramatic episode, in early September, was fueled by an unusually strong surge of surface high pressure that pushed powerful winds across hills and mountains toward the coast from Washington to California. The bizarre setup behind this event took shape downstream from intense typhoons in the Pacific – an outcome conceivably influenced by climate change, as argued recently on this site by meteorologist Jeff Masters.
In its fourth year in a row of catastrophic blazes, California suffered through five of its six largest wildfires in modern records. Colorado endured its three largest wildfires in modern history. Massive areas of thick smoke spread across the West and beyond, producing apocalyptic skies over such cities as San Francisco, and the smoke persisted for weeks to months in some areas. Health impacts from wildfire pollution typically lead to 5,000 – 15,000 “excess” deaths, according to a research group at Stanford University, but “smokier years like 2018 or 2020 will have a much higher death toll,” the team warned in October.
Preliminary data for 2020 show a below-average total of 1,053 U.S. tornadoes in 2020. The National Weather Service office in Wichita, Kansas, which issues an average of 36 tornado warnings per year, didn’t issue a single one in 2020. However, the season made up in impact what it lacked in numbers, especially across the South. There were several multi-billion dollar severe weather events, including a major tornado outbreak on April 12-13 from Texas to Virginia and another on April 22-23. Deadly tornadoes also slammed middle Tennessee, including Nashville, on March 2-3.
The annual tornado-related death toll of 78 was the highest since 2011, as was the number of killer tornadoes (25).
A ruined tree and damaged shed on the grounds of the historic Seminole Valley Farmstead just west of Cedar Rapids, Iowa, on October 8, 2020, a few weeks after the derecho of August 10. (Image credit: James Heires / Wikimedia)
The most freakish severe weather event was the ferocious derecho (a thunderstorm-driven corridor of damaging winds) that plowed across Iowa and northern Illinois on August 10. Hundreds of thousands of trees and millions of acres of crops were damaged or destroyed. Prolonged power outages added to the misery, especially in Cedar Rapids, Iowa; half the city’s entire tree canopy was destroyed.
As the derecho weakened, the associated thunderstorms spun out 15 tornadoes in northern Illinois, including an EF1 tornado in the Rogers Park neighborhood of Chicago. It was the city’s strongest twister since 1976.
With inflation-adjusted damage now estimated at $11 billion, the storms that drove the derecho rank as the most destructive thunderstorm complex in U.S. history, far exceeding any tornadic supercell on record. The event ranked #3 on 2020’s list of U.S. disasters, actually topping all of the hurricanes except for Laura.
A modest bit of consolation: the year’s death toll from U.S. weather disasters of 262 (outside of the pollution-related deaths noted above) was slightly lower than the long-term average. One such event that easily could have been worse was Category 4 Hurricane Laura, which slammed into southwest Louisiana packing top winds of 150 mph – tying as the state’s strongest hurricane landfall on record in terms of peak wind.
Lake Charles experienced a bona fide catastrophe with Laura. The hurricane took dozens of lives, structural damage was widespread, and life was massively disrupted for weeks on end. The impact on Lake Charles was compounded by the arrival of Category 2 Hurricane Delta in October. Yet Laura’s path ended up just east of the most dangerous trajectory, a path that could have pushed a highly destructive storm surge into the city and caused even more misery.
As the nation moves into early 2021, the biggest looming weather threat appears to be drought, especially for the Southwest (including California). La Niña winters and springs are typically dry across the Sunbelt, and that’s certainly been the case in recent weeks for most of the nation’s southern tier.
For the first week of 2021, the U.S. Drought Monitor showed 46% of the contiguous U.S. at some level of drought, compared to just 11% in the first week of 2020. Nearly all of the Southwest was in extreme to exceptional drought. Winter storms have been stingy in California thus far: as of December 31, the statewide snowpack was just 52% of average.
NOAA’s latest drought outlook, issued December 17, calls for drought to persist through at least March across the Southwest and to intensify from the Southern Plains to parts of Georgia and Florida. Not shown are the outlooks for Alaska, Hawaii, and Puerto Rico, where no droughts are expected to develop or intensify. (NOAA/NWS Climate Prediction Center)
Severe weather may also rear its head noticeably in early spring. As noted by climate.gov, La Niña winters can lead into particularly serious severe-weather episodes from March to May, especially across the Southern Plains. The two most destructive U.S. tornado outbreaks on record – in April 1974 and April 1991 – both followed La Niña winters, as did the hyperactive tornado season of 2008.
Moderately strong La Niña conditions have been in place since autumn, according to NOAA. While most computer models call for the event to weaken this spring and end by summer, several, including the leading NOAA and NASA climate models, indicate that at least borderline La Niña conditions could continue through summer and perhaps even reintensify in fall 2021. Some researchers are now focusing on multi-year La Niña events, which could in theory provide more than a year’s worth of useful lead time for some seasonal outlooks.
Posted by Guest Author on Monday, 22 February, 2021
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