April Keeps the Warm, Wet U.S. Trend Going for 2016

Although the warmth was notched down a bit from the year’s first quarter, April was still much milder and moister than average, according to the monthly U.S. climate roundup released on Wednesday by the National Centers for Environmental Information. The monthly average for the contiguous 48 states came in at 53.2°F, which is 2.2°F above the 20th-century average and the 18th warmest among the 122 Aprils since records began in 1895. Outside of New England, New York, Pennsylvania, and Michigan, every state came in above its long-term average (see Figure 1), and it was a top-five warmest April for Idaho, Oregon, and Washington. The only place that saw record statewide warmth in April was Alaska, which merits a separate discussion (see below).


Figure 1. Statewide rankings for average temperature during April 2016, as compared to each April since 1895. Darker shades of orange indicate higher rankings for warmth, with 1 denoting the coldest month on record and 122 the warmest. Image credit: NOAA/NCEI.


Figure 2. Statewide rankings for average precipitation during April 2016, as compared to each April since 1895. Darker shades of green indicate higher rankings for moisture, with 1 denoting the driest month on record and 122 the wettest. Image credit: NOAA/NCEI.


There were plenty of April showers this year, especially across the Great Basin and Great Plains. The month came in as the 21st wettest on record for the 48 contiguous states, with a 48-state reading of 2.95” (0.43” above the 20th-century average). It was a top-ten wettest April for the entire Plains corridor from Texas to North Dakota (Figure 2). The apex of last month’s precipitation was the phenomenally heavy rain and severe flash flooding in Houston on April 18. More than than a foot of rain fell in northwest parts of the Houston area, and the city officially saw its second wettest day on record (9.92”, topped only by 10.34” during Houston’s “first” Tropical Storm Allison in 1989). Across the southwest U.S., where moisture was scant earlier this year despite the strong El Niño, generous precipitation finally arrived.

Daily record highs are far outpacing record lows this year
It’s no longer quite the warmest year on record for the United States thus far (although the planet is still demolishing year-to-date records--stay tuned for our global roundup next week). The average temperature for the contiguous U.S. (January-April 2016) now ranks second behind only 2012. The tally of daily record highs and lows across the nation reinforces this warm picture: as of Wednesday morning, the year-to-date tallies on NOAA’s Daily Weather Records site show a total of 10,328 record daily highs and just 1286 record lows, a ratio of just over 8:1. Last year’s ratio ended up close to 3:1, after two oddly chill years in which the nation saw more daily record lows than highs (no such years had occurred since 1993).

By this date in 2012, the contiguous states had already seen thousands more record highs than in 2016, thanks to the Great Warm Wave of March 2012. However, 2016 has by far the lowest number of daily record lows to date of any year in the century-plus database--a reflection of this winter’s moist, mild El Niño conditions on top of long-term warming.


Figure 3. A picture of Alaska’s warmth in the first 110 days of 2016 as projected in the 6-10 day NOAA outlook for each day (advancing from left to right in each row and then from top row to bottom row). Orange and red colors denote above-average readings and blue below average. Nearly every day ended up with above-average readings throughout all or most of the state. Only one day--February 19--saw below-average readings the state as a whole. Image credit: Brian Brettschneider.


Crazy Alaskan warmth
The nation’s 49th state is setting the pace this year for temperature extremity. Alaska’s average for April of 33.3°F beat the previous record of 32.9°F (1940) and was a full 10°F above the 1925-2000 average, a huge margin for a state so large. For the year to date through April, Alaska’s 21.7°F came in almost 2°F above its previous record (18.9°F, 1981) and 11.4°F above the state’s long-term average. The consistency of this year’s warmth has been nothing short of amazing, with most Alaskan towns and cities recording only a handful of days below average thus far.


Figure 4. January through April 2016 is running far milder than all other years in the weather history of King Salmon, Alaska. Image credit: Brian Brettschneider.


Figure 5. Based on data through early May drawn from 25 locations across Alaska, this year’s consistent mildness has put 2016 ahead of all other years since 1955. Image credit: Brian Brettschneider.

Melting, melting
Rivers across Alaska are feeling the heat, with some showing record-early ice melt. “This is an under-appreciated issue, as most of Alaska is off the road network and frozen rivers are the most efficient method of travel,” noted meteorologist Brian Brettschneider in an email. At the town of Circle in east central Alaska, the Yukon River began flowing freely on April 29, the earliest ice break-up date on record and well in advance of the average date (since 1980) of May 10.

The break-up of the Tanana River at the town of Nenana provided a major windfall for 28 participants this year in the annual Nenana Ice Classic. Each year a jackpot is split among the hundreds of thousands of guesses as to which day the Tanana will experience its spring break-up at downtown Nenana. This year’s $330,330 winnings were divided evenly among the 28 entrants who correctly pegged the date as April 24. It was the seventh earliest breakup in the 99-year history of the contest, which began when a group of railroad engineers pooled $800 (in 1917 dollars). The average break-up date is now about a week earlier than it was in the early 1900s, as shown in this climate.gov feature.

Bob Henson


Figure 6. A tripod sits atop the Tanana River during the 2008 Nenana Ice Classic. When the river begins flowing, it moves the tripod and triggers a clock to stop, serving as the official marker of the ice break-up. Image credit: Wikimedia Commons/Frank K.


Figure 7. As of May 10, 2016, only a few rivers across far northern Alaska remained ice-choked. Image credit: NOAA/NWS Alaska-Pacific River Forecast Center.