Third Warmest October in U.S. Weather Records

Unusual autumn warmth was spread generously across the United States--but rainfall was hogged by the periphery of the nation--during October 2016, according to the monthly U.S. summary released by NOAA’s National Centers for Environmental Information (NCEI) on Tuesday. For the 48 contiguous U.S. states, October came in as the third warmest of the 122 Octobers in data extending back to 1895. This means that three of the six warmest Octobers on record have occurred in the last three years: 2014 (#6), 2015 (#5) and 2016 (#3). Still on top of the list for October warmth are 1963 (#1) and 1947 (#2).

On a statewide level, this year produced the warmest October on record for New Mexico, and 22 other states had a top-ten warmest October. Only one of the 48 contiguous states ended up cooler than average. That was Oregon, in large part because of the soggy, sun-blocking pattern that prevailed across the Pacific Northwest.


Figure 1. Statewide rankings for average temperature during October 2016, as compared to each October 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 October 2016, as compared to each October 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.

Stark contrasts in wetness and dryness
The contiguous U.S. had its 49th wettest out of the last 122 Octobers, but much more telling details emerge as we shift to the state and local scales. A relentless stream of storms swept across the Pacific Northwest and into the northern Rockies during October, giving large swaths of the region their heaviest precipitation for any October. The states of Washington, Idaho, and Montana all had their wettest October on record, and both Oregon and California placed in the top five (the latter mainly because of rains in the northern half of the state). Spokane, WA, saw its wettest month in 135 years of recordkeeping, with a total of 6.23”. Across the Southeast, the extreme rains from Hurricane Matthew over eastern North and South Carolina were enough to give SC a top-ten wettest October. Although the same wasn’t true for NC, plenty of local rainfall records were set, and the state’s inland flooding was severe, affecting an estimated 100,000 structures. Heavier-than-average rains also prevailed across the Upper Midwest, Great Lakes, Northeast, and New England, including areas struggling with drought for much of this year.

Meanwhile, a belt of less-than-average precipitation extended across the nation’s Sunbelt from Arizona to the southern Appalachians. The states of Alabama, Colorado, Louisiana, Mississippi, Tennessee, and Texas all had top-ten driest Octobers. Georgia was truly a divided state, as reflected in the percentile maps below. Little or no rain fell in parts of northwest Georgia--Atlanta received only 0.16”, less than 5% of its average rainfall for October--while Matthew brought phenomenal totals to parts of the southeast Georgia coast, including 17.49” at Savannah’s Hunter Army Air Field. NOAA’s winter outlook calls for drier-than-average conditions to prevail across the southern tier of the nation through the next few months.


Figure 3. Temperature and precipitation percentiles for the contiguous U.S. for October 2016. Produced by mapping U.S. data onto a grid with 5-kilometer-wide cells, these maps allow for finer-scale regional analysis. Pockets of record heat are most evident over New Mexico and western Texas, with record dryness over parts of far western Florida and Alabama. Image credit: NOAA/NCEI.


Figure 4. Chris Moore walks down Martin Luther King Blvd. on October 12, 2016 in Lumberton, NC, one of the areas hardest hit by inland flooding associated with Hurricane Matthew. Image credit: Sean Rayford/Getty Images.


Figure 5. Temperatures for the period from January through October for the contiguous U.S., 1895 - 2016. Image credit: NOAA/NCEI.


For the year to date (January - October), 2016 is running just behind 2012 for the title of warmest year in U.S. record-keeping history (see Figure 5 above). In order to come out on top, this year would have to generate the nation’s warmest November and December on record--and then some--so a #2 finish appears much more likely. The planet as a whole remains on track for its warmest year on record, a topic we’ll cover in more depth in our October global climate summary next week. The United States only represents about 2% of Earth’s surface area, so we wouldn’t expect U.S. temperatures to rise and fall in lockstep with the globe’s overall warming trend. When this does occur, it’s often in association with a year that begins with a strong El Niño in place, as was the case this year. Another good example is 1998, when both the United States and the planet as a whole had their warmest years on record (up to that point) in the wake of the record-setting 1997-98 El Niño.

When it comes to climate extremes, 2016 is making its mark nationally. NCEI’s U.S. Climate Extremes Index for the year to date (Jan - Oct) shows that 44.4% of the contiguous U.S. has experienced at least one of the five primary heat- or precipitation-related extremes that make up the index. This puts 2016 in third place behind 2012 and 1934 for the largest areal coverage of extreme conditions. When tropical cyclones are factored in, 1998 nudges into second place, pushing 2016 into fourth place. Not surprisingly, the main reason why 2016 ranks so high on the list is this year’s record-warm minimum temperatures, a topic we explored in depth in late October.

We’ll be back with a new post on Thursday.

Bob Henson