Average annual rainfall trending up

Published: May. 22, 2019 at 8:45 PM CDT
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Madison officially picked up .35 of an inch of rain Tuesday into Wednesday. For the month of May, the total stands at 3.41 inches. This is almost an inch above the average to date. This wet pattern is nothing new as we have pushed through the first few months of 2019. New data from our partners at Climate Central show that increased rainfall and wet periods, like we have had recently and over the last few years, could become the new normal.

A SOGGY MONTH: Rain totals over the last 36 hours came in between .25-.75 of an inch. For the month now we are running almost an inch above normal! More days than not have featured wet weather through May.

Posted by Meteorologist Brian Doogs NBC15 on Wednesday, May 22, 2019

As recent flash flooding in the Southeast made clear, heavy rain just will not stop. This year has brought longer-lived rain, helping areas of the Mississippi stay above flood stage for at least three months. That’s the longest stretch since the Great Flood of 1927 — the most destructive river flood ever in the modern U.S. Overall, the nation’s year-to-date rainfall is well above average, in line with the increased annual precipitation observed in most of the country.

From 1950 to 2018, average annual precipitation has risen in 90% of the U.S. states analyzed. Eighteen states have recorded an increase of five inches or more, led by New Hampshire (7.0 inches), Vermont (7.0 inches), and Indiana (6.6 inches). The eight largest increases have all come in the Northeast and Midwest, where downpours are also intensifying the most. Wisconsin is averaging 4-6 more inches of rain a year since the 1950.

Only five Western states are trending drier, including Oregon, California, Idaho, Washington, and Arizona. Though these decreases are all less than three inches, an inch or two can make a major difference in the drier West (where many states receive less than 25 inches per year). And even for the drier states, single downpours are still getting stronger.

2019 is taking some trends to the extreme. According to data analysis from Climate Engine, the great majority of the country has experienced above-average rainfall so far this year. Vast swaths of the Eastern interior have measured anomalies of 6 inches or more, which usually means at least 30% above average. Parts of the Midwest and Rockies are 50% to 100% above average. As of May 22nd, Madison sits at 13.05 inches of rain. That is a surplus of 2.34 inches on the year!

Only the Pacific Northwest, coastal Southeast, and spots in the Plains have observed below-average precipitation. In fact, the last 12 months have been the wettest on record.

Climate change has a mixed effect on overall precipitation, altering weather patterns that may vary by season and latitude. However, the impact on heavy rain is much clearer. As higher temperatures supercharge the water cycle, downpours are getting stronger and amplifying flood risks. This year’s extremes exemplify the impacts of our already warming world.

Each state’s change in average annual rainfall since 1950 was calculated using a mathematical linear regression. Data obtained from NOAA/NCEI Climate at a Glance. Hawaii and Puerto Rico did not have data available. Year-to-date precipitation data for the contiguous U.S. was obtained from the METDATA set (via Climate Engine) as of 5/22/19. Percentages are relative to the 1981-2010 climate normals.

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