365 Days of Climate Awareness 171 – 2019 State of the Climate, North America

2019 US Climate Data

• Global atmospheric CO₂ concentration: 410.07 ppm, +2.45 ppm from 2018
• Average air temperature: 54.2°F, 48^th all-time 1895-2021
• Average precipitation: 34.82”, +4.88” over mean
• Tornadoes: 1517, 178 (24%) above the 1991-2010 average 1251
• 18 named tropical cyclones: 6 hurricanes, 3 major (winds > 111 mph, 3-5 Saffir-Simpson)
• Atlantic ACE: 143.78 x 10⁴ kts² (1991 - 2020 mean: 108.7 x 10⁴ kts²)
• ENSO: Weak E. Niño early, neutral the rest of the year

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North American Conditions

• Warmer than average: Northern Canada (above 60°N); southeastern US; Mexico
• Cooler than average: Southern Canada (below 60°N); upper midwestern US
• Drier than average: Northwestern and central southern US; northeastern, central and southern Mexico
• Wetter than average: Midwestern and southwestern US; northwestern Mexico
• Wildfires: Below average in Canada and the US
• Snow cover: 25.4 x 10⁶ km² winter maximum vs 1966 - 2020 average 25.1 x 10⁶ km²

The Atlantic hurricane season was again above-average in both storm count (18 vs. 12.1 average 1981-2010) and ACE (143 vs 104 x 10⁴ kts² 1981-2010 average). Most of the storms were brief and unusually far north. Tropical Atlantic sea surface temperatures (SSTs) fluctuated around their long-term means all year but warmed a bit in late summer and fall with the emergence of an Atlantic Niño.

A series of severe spring floods struck eastern Canada along the Ottawa and St. Lawrence Rivers. The 2018-19 winter was unusually cold, leading to a very deep frost which did not thaw by spring, so the deep snowpack did not infiltrate the ground as it melted. In addition 1.5 m of rain fell on the region in April and May. These combined influences caused the rivers to overflow, killing two and damaging more than 6000 homes. Flooding also occurred in New Brunswick, leading to 5500 homes damaged or threatened.

2019 US Percentage Area Very Warm vs Very Cold (top 10th percentile for each).  

Permafrost responds to surface temperature variations in two principal modes. The first mode is the upper zone prone to melting (the “active layer”), which responds to shorter variations such as the alternation of seasons and other changes on the timescales of weeks to a few years. The second mode is the deeper, permanently frozen zone, which responds to long-term climatic change. The varying thickness of the upper, freeze/thaw zone, is a combination of both. Across the Arctic the frozen permafrost has been warming in recent years, on the scale of 0.3-0.8°C (0.5-0.9°F) per decade. Upper-layer melt has been occurring earlier in the year, and refreeze later. Active layer thickness (ALT) has increased across the northern hemisphere, in some cases by nearly 0.1 m. Furthermore, during winter in some areas the active layer does not freeze all the way down to the underlying permafrost.

2019 US Percentage Area Very Wet vs Very Dry (top 10th percentile for each).  

Tomorrow: 2019 state of the world climate.

Be brave, and be well.