A Top 20 Cold April for the 48 Contiguous States

Last month was the 13th-coolest April in 124 years of recordkeeping for the contiguous U.S., according to the monthly climate roundup released on Tuesday by NOAA. Canada likely experienced one of its coldest Aprils on record, although the verdict is not yet available from Environment Canada.

The chill stands out like a sore thumb in a global perspective. This was one of the warmest Aprils on record for the planet as a whole, as reported by Capital Weather Gang. In fact, compared to local averages, North America was the coldest region on Earth last month. We’ll cover the global picture in more detail later this month.

It was the third hottest April on record (after 2016 and 2017), says @CopernicusECMWF. Average temperature for 12-month period from May 2017 to April 2018 was most above average in Arctic and, globally, was 0.47°C warmer than 1981-2010 baseline. #climatechange pic.twitter.com/REFIU6k3pw

— WMO | OMM (@WMO) May 7, 2018

Remarkable chill east of the Rockies

A total of 21 U.S. states had a top-ten coldest April, and two states—Iowa and Wisconsin—saw their coldest April on record. In both of those states, previous records set in 1907 were smashed by at least 1.5°F, an impressive margin for a statewide monthly temperature record (especially a cold record in a warming climate). Moreover, each state adjoining Iowa and Wisconsin had its second coldest April on record. Some of those states might have hit #1 had it not been for a surge of very warm air that arrived on the last day of April.

Here are a few of the U.S. cities that saw their coldest April on record. Many others had their second- or third-coldest.

Cooperstown, NY:  33.7°F (old record 37.2°F in 1907; records began in 1893)
Rochester, MN:  34.5°F (old record 37.6°F in 1950; records began in 1886)
Sioux Falls, SD:  37.5°F (old record 37.8°F in 1950; records began in 1893)
Spencer, IA:  36.6°F (old record 39.8°F in 1951; records began in 1895)
Flint, MI:  39.1°F (old record 39.4°F in 1950; records began in 1921)
St. Joseph, MO:  45.9°F (old record 46.6°F in 1983; records began in 1908)
Mineral Wells, TX:  60.2°F (old record 60.5°F in 2007; records began in 1948)

Figure 1. Statewide rankings for average temperature for April 2018, as compared to each April since records began in 1895. Darker shades of blue indicate higher rankings for cold, with 1 denoting the coldest month on record and 124 the warmest. Image credit: NOAA/NCEI.

Snowfall added to the misery for many. Chicago picked up measurable snow (at least 0.1”) on six days last month, the most for any April except 1910. In New York’s Central Park, the 5.5” of snow on April 2 was the most for any April day since 1982. As noted by weather.com’s Chris Dolce, the average snow cover extent in the Lower 48 was the fifth largest for April in records maintained by Rutgers Global Snow Lab that go back to 1967.

Cold nights were a hallmark of last month. In nine states from Minnesota to Mississippi, the average of the daily lows last month was the lowest for any April on record. Chicago saw freezing temperatures on 16 days, the most for any April in records going back to 1872. Unusually late freezes and prolonged chill helped put a damper on vegetation, with leaf-outs as much as three weeks later than usual across much of the Midwest and Northeast.

It wasn’t chilly across the whole country, though, as unusual warmth prevailed from the Rockies westward. Arizona notched its second warmest April on record. In El Paso, Texas, the monthy average of 70.6°F beat the old record of 70.3°F from 2011; records in El Paso began in 1887.  Also notching its warmest April on record was Needles, CA (79.2°F, beating 78.2°F from 1989; records began in 1888).

Figure 2. Average April temperatures across Wisconsin, 1895-2018. Image credit: NOAA/NCEI (annotated by WU).

Figure 3. Average April temperatures across Arizona, 1895-2018. Image credit: NOAA/NCEI (annotated by WU).

Months that are this cool over the contiguous U.S. relative to the 20th-century norm have been in short supply during the 21st century. Below is a list of the last time each calendar month placed in the Top 20 coolest for that month in records going back to 1895. Several of these months were associated with red-letter weather and climate events, including the epic cold waves of January 1985 and February 1989, the Midwest’s Great Flood of 1993 (which intensified in June), and the blizzard that raked the eastern U.S. and Canada in December 2009. Interestingly, the second half of the year has seen more recent Top 20 cold months than the first.

January: 1985
February: 1989
March: 1975
April: 1997 (and now 2018)
May: 1995
June: 1993
July: 2009
August: 2004
September: 2006
October: 2009
November: 2014
December: 2009

Just a reminder: Global warming didn’t stop in April

Needless to say, an occasional cold month doesn’t negate the long-term temperature rise occurring both nationally and globally as a result of human-produced greenhouse gases. The national average for April has risen about 1°F over the last century, as shown in the time series below—and Figure 2 above makes it clear just what an outlier this April was in Wisconsin.

Figure 4.  Average April temperatures across the contiguous U.S., 1895-2018. Image credit: NOAA/NCEI.

A slightly drier-than-average month nationwide

U.S. precipitation extremes tended toward the muted side during April. The contiguous U.S. saw its 53rd-driest April in 124 years of recordkeeping. Relatively moist conditions prevailed east of the Mississippi and along the Pacific Coast, sandwiching dryness across the Southern Rockies and Great Plains.

It was a top-ten-driest April for Arizona, Kansas, Missouri, and New Mexico, and the third-wettest April on record for the state of Washington.

Figure 5.  Statewide rankings for average precipitation for April 2018, as compared to each April since records began in 1895. Darker shades of green indicate higher rankings for moisture, with 1 denoting the driest month on record and 124 the wettest. Image credit: NOAA/NCEI.

Warmest year on record so far in America’s southernmost state capital—and in its northernmost city

Through April, the year to date is only slightly above average for the 48 contiguous states (it’s the 42nd-warmest in 124 years of data). However, for two of America’s most far-flung cities, 2018 is the warmest year on record so far. Honolulu, Hawaii, averaged 76.1°F for the period January through April, which is the highest in 69 years of recordkeeping.

At Utqiaġvik (Barrow), on Alaska’s Arctic coast, this year’s Jan-Apr. average of 1.2°F is more than 10°F above the 1981-2010 norm and the warmest in 96 years of recordkeeping. Incredible mildness has swaddled Alaska this winter, in tandem with the earliest decline of sea ice ever recorded in the Bering Sea. In Utqiaġvik, each of the last three winters (December-February) has set a new record high, and the winter of 2017-18 was the first to notch an average temperature above 0°F. The Guardian filed a compelling report last month on life in Utqiaġvik amid a rapidly warming climate.

Figure 6. Average temperature for winter (December-February) in Utqiaġvik (Barrow), Alaska, from 1920-21 to 2017-18. Each of the last three winters has been warmer than any previously observed. Image credit: NOAA Regional Climate Centers.