365 Days of Climate Awareness 157 – 2012 State of the Climate, North America

2011 US Climate Data

• Global atmospheric CO₂ concentration: 392.65 ppm, +2.02 ppm from 2011
• Average air temperature: 57.0°F, 1^st all-time 1895-2021
• Average precipitation: 24.65”, 114^th wettest (14^th driest) 1895-2021
• Tornadoes: 1625, 355 (28%) above the ten-year average 1253
• 19 named tropical cyclones: 10 hurricanes, 1 major (winds > 111 mph, 3-5 Saffir-Simpson)
• Atlantic ACE: 139.46 x 10⁴ kts²
• ENSO: Weak La Niña early 2012, neutral the rest of the year

Larger Version

North American Conditions

• Warmer than average: Canada; United States (especially the Northeast, Midwest and South); Mexico
• Drier than average: Upper midwestern & southern US
• Wildfires: 67,265 wildfires burned 3.7 million ha/9.1 million acres in US (third most at the time)

2012 was the warmest year for the continental United States in the historical record, and it included the fourth-warmest winter. The wildfire count involves a below-average number of fires but extensive area burned, implying that many of the fires were extremely large. In keeping with the warmth of the winter, the United States experienced its third-lowest recorded snowfall.

2012 featured Hurricane (Superstorm) Sandy, which formed in October, swelled to Category 3 before hitting Cuba, and then continued north, changing from a Tropical Cyclone (TC) to an Extra-Tropical (or Post-Tropical) Cyclone (ET/PT). On October 29 Sandy reached New Jersey still having some of the symmetrical “warm-core” TC structure, but no longer classified as a hurricane as it increasingly gained extra-tropical, cold-core characteristics. (It is not rare for a tropical cyclone to become extratropical, and maintain hurricane-speed winds.)

2012 Percentage of US Area Very Warm vs Very Cold (10th percentile for each)  

Three things are needed for a TC to change into an ET: (1) a large enough temperature and density difference in the atmosphere ("baroclinic zone" for the wonkish, meaning air density is a function mostly of temperature, not elevation); (2) a large pool of warm seawater; and (3) a strong enough existing storm. The TC becomes an ET when the primarily warm air in the tropical eye becomes cooler subtropical air in the storm's center but the storm retains its energy.

2012 Percentage of US Area Very Wet vs Very Dry (10th percentile for each)

All three conditions were met in Sandy. Another low-pressure system to the east forced Sandy west and it made landfall in New Jersey no longer classified as a hurricane, but combined with a lunar spring tide generated a storm surge as high as 40 feet and did more than $60B in damage to both New Jersey and New York.

Tomorrow: 2012 State of the World Climate.

Be brave, and be well.