|Above: Pedestrians navigate Times Square in New York City, during a snowstorm on Jan. 4, 2018. Image credit: Michael Brochstein/SOPA Images/LightRocket via Getty Images.|
Would you believe that the contiguous U.S. just had its 25th-warmest January in 124 years of recordkeeping? Or that Minnesota, Michigan, and Maine all ended up with a warmer-than-average January? For a month that opened with an exceptional, record-shattering cold wave, January 2018 ended up surprisingly mild when averaged for the contiguous U.S. as a whole.
There’s no doubt January will be best remembered by millions for the epic cold blast that lodged itself over central and eastern North America from around Christmas through the first week of the new year. Dozens of locations across the Midwest and East had their coldest or second-coldest holiday week and/or first week of January on record. Although the chill didn’t set many all-time record lows, it was intense as well as persistent. In mid-January, another blast of Arctic air came and went more quickly. It still managed to produce the coldest temperatures observed in 20 to 30 years over parts of the South.
|Figure 1. Temperature rankings for the period Dec. 23, 2017 through Jan. 5, 2018, relative to the same period in prior years. Cities in purple boxes denote those that had at least a top-five-coldest Dec. 23 through Jan. 5 period on record in 2017-2018. Image credit: Southeast Regional Climate Center, via weather.com.|
What got less attention last month was the unusually mild weather that prevailed west of the Rockies throughout the month. As shown in Figure 2 below, every state west of the Great Plains except New Mexico and Montana—nine states in all—had a top-ten warmest January on record, including Arizona (second warmest) and Nevada and California (third warmest). Some of that mild Pacific air pushed across the nation later in the month, which helped offset the early-January cold. Not a single contiguous state ended up with a top-ten coldest January, although it was the 15th-coldest for Louisiana and 17th-coldest for Mississippi and North Carolina.
|Figure 2. Statewide rankings for average temperature during January 2018, as compared to each January since 1895. Darker shades of orange indicate higher rankings for warmth, with 1 denoting the coldest month on record and 124 the warmest. Image credit: NOAA/NCEI.|
The midmonth whiplash from unusual cold to unusual warmth was especially striking in the upper Midwest and New England. In Burlington, VT, a daily record low of –20°F on Jan. 7 was followed by a record high of 61°F on Fri., Jan. 11. By Sunday morning, Jan. 13, temperatures were back down to –5°F. International Falls, Minnesota—nicknamed the “icebox of the nation”—dipped to –36°F on Jan. 12 and 13, setting record lows on both days. Less than a week later, on Jan. 19, the city set a record high with 43°F. The month as a whole averaged 5.4°F at International Falls, not exactly swimsuit weather but still 1°F above the city’s 1981-2010 average.
|Figure 3. Statewide rankings for average precipitation during January 2018, as compared to each January since 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.|
A month of expanding dryness
Storm after storm rode the jet stream from the central U.S. toward the Northeast in January. However, this pattern wasn’t conducive to pulling in large amounts of Gulf or Atlantic moisture, so most of the systems were paltry precipitation-producers. One sweet spot for winter weather was a belt from Texas to the mid-Atlantic. Some locations such as Houston that can go years without frozen precipitation got their third snow event of the winter. Another swath of noteworthy (albeit less unusual) snowfall extended from the Upper Midwest across the Great Lakes states into New England. The state of Washington also made out well moisture-wise, notching its 31st-wettest January on record.
Otherwise, the national picture for January was a largely dry one, especially for the Southern Plains and Appalachians. It was the 10th-driest January on record in New Mexico and the 9th-driest in Alabama. Only eight of the 48 contiguous states had monthly precipitation that was significantly above average (see Figure 3 above).
In Amarillo, Texas, January was the third consecutive month without any measurable precipitation, extending a dry streak that tops anything in records that include the 1930s Dust Bowl.
From Jan. 2 to Jan. 30, the amount of the contiguous U.S. covered by severe to exceptional drought more than doubled (rising from 7.46% to 17.21%), according to the National Drought Mitigation Center. By Jan. 30, more than two-thirds of the Lower 48 (67.10%) were covered by abnormally dry conditions, and snowpack had reached disturbingly low levels from Oregon to New Mexico southward, including California.
|Figure 4. U.S. Drought Monitor valid on Jan. 2, 2018 (left) and Jan. 30 (right). Image credit: National Drought Mitigation Center.|
The most tragic U.S. weather calamity of 2018 was the product of wetness as well as dryness. At least 21 people were killed (with two still missing) and 28 injured by a flash flood that tore through the coastal community of Montecito, California, in the predawn hours on Jan. 9. The hillsides above Montecito were ravaged by wildfire in December after one of the driest autumns on record. Heavy overnight rains on Jan. 8-9 cascaded off a landscape partially sealed by the intense heat of the fire, carrying massive amounts of debris and ash into Montecito.
|Figure 5. Cal Fire’s Alex Jimenez walks through mud at a house along Glen Oaks Drive in Montecito, Calif., on Jan. 10, 2018, after heavy rains hit the wildfire-scorched hillsides and triggered flash flooding early on Jan. 9. A flood victim’s body was reportedly found beneath the mud. Image credit: Photo by Wally Skalij/Los Angeles Times via Getty Images.|
Finally, a month skewed toward record lows
After 36 consecutive months that each saw more daily record highs than lows, “the streak is over,” according to Guy Walton (@climateguyw). Walton, a meteorologist who’s been compiling NOAA statistics on record highs and lows for more than a decade, reported on his blog that January 2018 had a preliminary total of 2750 daily record lows versus 1918 daily record highs. “I was wondering when this thing would end, if ever, in my lifetime,” said Walton
It was the extension of the exceptional holiday cold blast into the new year that clearly did the trick. As reported by weather.com, dozens of cities from New York to Tallahassee and into the Midwest notched their coldest first week of January on record. The resulting avalanche of cold records was promptly followed by the familiar tendency toward warm records throughout the rest of the month.
According to preliminary data on NOAA’s Daily Weather Records website, the interval from Jan. 5 to Jan. 31 saw a total of 1783 daily record highs broken or tied, almost three times the 611 daily record lows broken or tied. And February is off to a rip-roaring start: the first three days of the month racked up a preliminary total of 151 daily record highs but not a single daily record low.