The Van Trump Report

Interesting… Long Term Weather Trends “Warmer” but also “Wetter”

We’ve all heard talk of getting warmer but I hadn’t noticed the wetter evidence. Once every decade, the National Oceanic and Atmospheric Administration (NOAA) updates its 30-year averages used to determine “climate normals.” The 1991–2020 U.S. Climate Normals are the latest in a series of decadal normals first produced in the 1950s. NOAA’s updated numbers are notably warmer than the previous period (1981-2010), with the average temperature raised to a new record high of 53.28. The new normals also reveal that the U.S. climate is wetter than in the previous decade. NOAA notes that many parts of the U.S. are actually projected to get wetter over time, especially toward the northern states.

Let’s first look at the upward shift in temperature averages, as we are learning, the warming trend varies by geography and time of year. The new averages include the decade from 2011-2020, which was the hottest on record in the U.S. and globally going back to 1880. The most substantial jump in the new U.S. average temperatures from the previous period were witnessed along the West Coast, in the South, and along the East Coast, but temps actually cooled somewhat in the Northern Plains and Upper Midwest, particularly in the spring. Over the longer term, the pace of warming in many places changes from decade to decade due to other climate influences, both natural and human (think the Dust Bowl and smokestack pollution before the Clean Air Act).

Overall, the annual average temperature in the U.S. in each 30-year normal period has trended warmer throughout the decades when compared to the longer-term 20th-century average (1901-2000). “The influence of long-term global warming is obvious: the earliest map in the series has the most widespread and darkest blues, and the most recent map has the most widespread and darkest reds,” said Rebecca Lindsey in a NOAA climate blog. Since 1901-1930, the first period for which climate normals were calculated, the contiguous United States has warmed 1.7 degrees.

The new normals also reveal that the U.S. climate is wetter than the previous decade. Preliminary data showed a national precipitation average of 31.31 inches for 1991-2020, up by 0.34 inches over the 1981-2010 value of 30.97 inches. The 20th-century average was 29.94 inches. However, the trends vary by region. The new decade averages show the Southwest has turned drier, while wetter averages emerged in the U.S. east of the Rocky Mountains, especially the Southeast in the spring.

NOAA notes that many parts of the U.S. are projected to get wetter over time, especially toward the northern states. Lindsey notes that precipitation—regardless of human-caused climate change—varies a lot from place to place across the United States. Few places exhibit a precipitation trend that is either steadily wetter or steadily drier than the 20th-century average. Instead, drier areas and wetter areas shift back and forth without an obvious pattern.

However, rainfall and snowfall appear to be trending toward clusters of intensified precipitation, separated in some cases by longer dry periods, particularly in California. There are also signs that a multi-decade megadrought may have already set in over the southwest U.S. and northwest Mexico. You can dive into the detailed data for the updated U.S. Climate Normals HERE. (Sources: NOAA)

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