|Above: The winter’s most catastrophic weather-related event was the Thomas Fire northwest of Los Angeles. Fed by strong, dry Santa Ana winds, the fire destroyed more than 1,000 structures as it tore across a drought-parched landscape, becoming the state’s largest wildfire in modern records. Here, the Thomas Fire burns in the Los Padres National Forest, near Ojai, Calif., on Dec. 8, 2017. Image credit: Marcus Yam/Los Angeles Times via Getty Images.|
In spite of some high-profile snowstorms and frigid outbreaks, meteorological winter (December-February) was the 24th warmest and 34th driest on record for the contiguous U.S., according to figures released Tuesday by NOAA’s National Centers for Environmental Information (NCEI).
Much of the winter featured a strong upper-level trough digging across the central U.S., occasionally migrating through the eastern states and encircled by a strong jet stream. This pattern—quite characteristic of La Niña, now in its second winter—led to a highly variable weather regime, with bouts of very cold air interspersed with some dramatic warm spells.
For most of the nation, the warmth outweighed the cold: only two states, Nebraska and Montana, were significantly colder than average. It was among the 10 warmest winters on record for California, Nevada, and the Four Corners states. Remarkable chill prevailed across the central and eastern U.S. for the two weeks surrounding New Year’s Day, which were the coldest or second coldest on record at many locations. Even so, the winter as a whole ended up among the 30 warmest in 124 years of recordkeeping from Alabama to Georgia and along most of the East Coast.
50% more record highs than record lows
Based on data compiled by meteorologist Guy Walton, the nation saw 6886 daily record highs and 4557 daily record lows from December through February. January was the first month since November 2014 that saw more daily record lows (2857) than highs (2357). The sharp cold of late December into January didn’t manage to set all that many monthly cold records, though. As a whole, the winter produced 356 monthly record highs versus just 119 monthly record lows.
|Figure 1. Statewide rankings for average temperature for winter 2017-18 (December-February), as compared to each winter since records began in 1895-96. Darker shades of orange indicate higher rankings for warmth, with 1 denoting the coldest month on record and 123 the warmest. Image credit: NOAA/NCEI.|
Precipitation was sparse for most of the winter across most of the nation. It didn’t take much moisture to produce the rare multiple snowfalls observed from the Texas Gulf Coast to southeast Georgia, but by late winter, very heavy rains developed across the Mississippi and Ohio Valleys, leading to widespread flooding. Arkansas ended up with its 4th wettest winter on record. Heavy snows across the Northern Rockies and adjacent plains gave Montana its 11th highest precipitation total for any winter on record.
With the jet stream largely bypassing California and Oregon, the Southwest U.S. saw a very dry winter, leaving snowpack across the region far below average. After some help from a snowy storm at the start of March, the water content measured at Phillips Station in the central Sierra Nevada on March 5 was at 39% of the average to date. (Fortunately, reservoirs are still amply stocked from last year’s precipitation bounty plus this year’s rains and snowmelt to date.) This past winter was the 2nd driest on record for California, the 8th driest for Nevada and Utah, and the 10th driest for Kansas.
|Figure 2. A cow grazes on a parched stretch of open range north of Albuquerque, N.M., on Thursday, Feb. 22, 2018. Officials with the Farm Service Agency in New Mexico said many ranchers were scrambling to buy up alfalfa reserves to supplement feed for their livestock as drought conditions were expected to intensify. Image credit: AP Photo/Susan Montoya Bryan.|
December brought California its largest wildfire in modern records, as the Thomas Fire scarred more than 280,000 acres in its rampage across parts of Ventura and Santa Barbara counties. Only one fire-related death was reported, but on January 9, flash flooding driven by heavy rains across the fire-scarred hillsides killed 21 people, most of them in the hard-hit coastal city of Montecito.
Extreme drought set in during the winter across the southern High Plains, focused on the Oklahoma and Texas Panhandles. Across parts of this region, it was the driest winter on record by far. Amarillo, TX, received a mere 0.01” of moisture from October 14 through the end of February, a period when average precipitation runs close to 4”. Guymon, OK, did little better than Amarillo, racking up a meager 0.05” for the period 10/14-2/28. Neither city saw any precipitation in the first week of March.
|Figure 3. Statewide rankings for average precipitation for winter 2017-18 (December-February), as compared to each winter since records began in 1895-96. Darker shades of green indicate higher rankings for moisture, with 1 denoting the driest month on record and 123 the wettest. Image credit: NOAA/NCEI.|
A high-contrast February
After several very dry months, the atmosphere switched gears last month, leading to the nation’s 6th wettest February since records began in 1895. While the southern High Plains saw virtually no moisture yet again, generous rains and snows fell across much of the Plains, Midwest, and Northeast—with too much in some areas. It was the wettest February on record for Arkansas, Illinois, Indiana, Missouri, Pennsylvania, and Tennessee, and a top-ten-wettest for nine other nearby states, plus Montana. Several spots from Michigan to Louisiana set February records for the highest amount of water vapor observed in the atmosphere, and the worst flooding in 20 years struck parts of the Ohio Valley, in part due to heavy rains falling atop frozen ground and snowpack in parts of the lower Great Lakes states.
Drought remained a problem in the Southwest, tempered only slightly from the end of the month into early March. It was the third driest February on record for California.
Looking at Downtown Cincinnati from across the flooded Ohio River in Newport, KY. Lots of people out this morning taking detoured running routes. Geese loving the extra water. #CincyWx #flooding @WCPO pic.twitter.com/cdcktgk0hP— Hillary Lake, WCPO (@hillarylake) February 25, 2018
|Figure 4. Statewide rankings for average precipitation during February 2018, as compared to each February 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 phenomenal burst of springlike mildness pushed temperatures to 77°F as far north as Maine and New Hampshire in February. Both Newark, NJ, and Washington, DC, notched their earliest 80°F readings on record, and more than 200 locations had their warmest February temperatures ever observed, as noted by Linda Lam in a February roundup at weather.com. The “warm wave” helped put February into record-warm territory for the Southeastern states of Alabama, Florida, Georgia, and North and South Carolina, as well as Connecticut, Massachusetts, and Rhode Island. Fourteen other states had a top-five-warmest February, while Montana had its sixth coldest.
|Figure 5. Statewide rankings for average temperature during February 2018, as compared to each February 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.|