The January-September period will go down as the third warmest on record but the wettest ever for the Lower 48, the National Oceanic and Atmospheric Administration said in its latest "State of the Climate" report released Oct. 16.
The average temperature for the January-September period was 57.7 degrees Fahrenheit, or 2.7 degrees above the 20th century average, trailing only January-September of 2012 and 2016. January-September precipitation totaled 26.36 inches, or 3.16 inches above average, surpassing the prior record set in 1979.
The year-to-date period saw above-average temperatures prevail across every state in the contiguous U.S. Forty-one states spread from coast to coast had much-above-average temperatures in the January-September period, including Florida, North Carolina and South Carolina that each had its warmest nine-month start to a year on record.
The average daytime temperature in the year-to-date period was 69.6 degrees F, or 2.3 degrees above average, making it the sixth warmest in the period of record going back to 1895. The average nighttime temperature for the same period was 45.8 degrees F, or 3.0 degrees above average, ranking as the third warmest ever recorded.
In terms of precipitation, most locations were wetter than average in the January-September period, with much-above-average precipitation observed across the West, as well as parts of the Southern Plains, central Gulf Coast and Great Lakes, where eleven states were much wetter than average. Below-average precipitation was seen across the Northern Rockies and Northern Plains. No state was record wet or dry in the January-September period.
The year-to-date period was capped by a September that was among the warmest third in the 123-year historical record, with an average temperature that was 1.4 degrees above average at 66.3 degrees F.
"The temperature pattern across the contiguous U.S. shifted dramatically in mid-September," the NOAA said. The early part of the month saw record to near-record warmth prevail over the West and colder-than-normal weather settle over the East, but conditions reversed in the last two weeks of September as record to near-record warmth gripped the East and colder-than-normal weather overtook the West. This pattern resulted in many states having near- to above-average September temperatures, with much-above-average temperatures observed in the central Great Lakes and Northeast, the agency said.
In September, the average daytime temperature was the 41th warmest since record-keeping began but coolest since 2014 at 78.8 degrees F, or 1.0 degree above average. The average nighttime temperature was 16th warmest ever recorded at 53.8 degrees F, or 1.9 degrees above average.
Based on NOAA's Residential Energy Demand Temperature Index, Lower 48 temperature-related energy demand in September was 30% below average and ranked near the middle value in the period of record.
Nationally-averaged September precipitation was 2.22 inches, or 0.27 inch below average, placing it among the driest third of the historical record.
Below-average September precipitation was observed for the mid- and lower-Mississippi Valley stretching into the Great Lakes and Northeast, where five states were much drier than average and Louisiana tied its driest September on record. Above-average precipitation extended from the Great Basin, through the Rocky Mountains and into the Northern Plains, as well as over portions of the Southeast, though only Wyoming was much wetter than average. Many mountain locations in the West received their first snow of the season.
Drought was observed for 14.4% of the contiguous U.S., up roughly 2.6% from the end-of-August figure, according to the Oct. 3 U.S. Drought Monitor. Drought conditions improved across parts of the Northwest and Northern to Central Plains, but expanded and intensified in portions of the Midwest and Southern Plains, as well as other parts of the Northwest.
The warm season was the 11th warmest in the period of record, with an April-September average temperature of 66.4 degrees F, or 1.4 degrees above average. Above-average temperatures spanned the West, Great Lakes and the East Coast, where 19 states had much-above-average temperatures, while near-average temperatures settled over the Great Plains and Southeast.
The average daytime temperature in the warm season was 79.0 degrees F, or 1.1 degrees above average, ranking as the 25th warmest on record. The average nighttime temperature over the same period was the sixth warmest on record at 53.9 degrees F, or 1.7 degrees above average.
Warm-season precipitation totaled 18.32 inches, or 2.08 inches above average, making it the ninth wettest April-September on record. Precipitation was above average for most of the West, Southern Plains, Southeast and Great Lakes into the Northeast, but below average for the Northern Rockies, Northern Plains and parts of the Midwest. No state was record wet or dry during the warm season.