365 Days of Climate Awareness 167 – 2017 State of the Climate, North America

2017 US Climate Data

• Global atmospheric CO₂ concentration: 405.22 ppm, +2.16 ppm from 2016
• Average air temperature: 56.4°F, 3^rd all-time 1895-2021
• Average precipitation: 32.31”, +2.37” over mean
• Tornadoes: 1429, 178 (14%) above the 1991-2010 average 1251
• 17 named tropical cyclones:10 hurricanes, 6 major (winds > 111 mph, 3-5 Saffir-Simpson)
• Atlantic ACE: 241.08 x 10⁴ kts² (1991 - 2020 mean: 108.7 x 10⁴ kts²)
• ENSO: Mostly neutral, weak La Niña early and late

Larger Version

North American Conditions

• Warmer than average: Northwest and central Canada; US outside of the Pacific Northwest; Mexico (record warmth at the time)
• Cooler than average: Southwestern, central and eastern Canada; northwestern US
• Drier than average: Upper Midwest and southwestern US; west coast of Mexico
• Wetter than average: Northwestern, Great Lakes region, Gulf Coast region and northeastern US; California; northern and south central Mexico
• Wildfires: Southern British Columbia; US wildfire activity (4.0  million ha/9.9 million acres) vs. 2.7 million ha/6.7 million acres 2000-2010 average
• Snow cover: 25.8x 10⁶ km² winter maximum vs 1966 - 2020 average 25.1 x 10⁶ km²

The Atlantic hurricane season was extremely active, even for a La Niña/neutral ENSO year. Three hurricanes (Harvey, Irma and Maria) struck the United States and did over $265B in damage, making it the costliest year in US history for weather and climate disasters (the total for all events was $306B).  September set an all-time record for hurricane activity, with five hurricanes, four of them major, active in the basin at the same time. The Accumulated Cyclone Energy (ACE) index for the month was 155.4 x 10⁴ kts², narrowly edging out September 2004 (155.0 x 10⁴ kts²) for the most active month for Atlantic cyclones in US history.

Hurricane Harvey formed in the Caribbean in August, and after crossing the Yucatan Peninsula, struck southwest of Houston on August 25 as a category 4 hurricane, the strongest cyclone to make landfall in Texas since Carla in 1961. The storm brought a 3 m surge and moved very slowly, and though it weakened to tropical storm status, circled back to the southeast and, back over water, moved northeast toward Louisiana while continuing to impact the metropolitan area of Houston before continuing northeast through Louisiana, toward Ohio. Over those five days Harvey dropped an average 84 cm of water—more than a trillion gallons--on Harris County, where Houston is located, with a maximum of 1.5 m recorded in Nederland, near the Texas-Louisiana border.  15,000 homes were destroyed and another 25,000 damaged.

2017 US Percentage Area Very Warm vs Very Cold (top 10th percentile of each)

2017 US Percentage Area Very Wet vs Very Dry (top 10th percentile of each)

Tomorrow: 2017 state of the world climate.

Be brave, and be well.