Scary Warm: Welcome to the Halloween Heat Wave of 2016
By: Bob Henson , 3:55 PM GMT on October 28, 2016

   
Trick-or-treaters and adult partygoers will be doing their best to keep their cool over the next several days. It’s been seasonally chilly and even snowy across parts of the Northeast, but Phoenix saw its latest-in-any-year 100°F reading on Thursday. Over much of the central and eastern U.S., temperatures will soar to unusually warm heights as we roll through All Hallows’ Eve and into the first several days of November. Temperatures on Halloween (Monday, October 31) are projected to reach the 70s from South Dakota to West Virginia and the 80s from Kansas to the Carolinas. As a very strong Pacific jet continues to pump mild air into the nation, we could see a few all-time monthly records for November threatened later next week, especially across the U.S. South. Here’s a day-by-day guide from weather.com on the warmth next week could bring.

Even more noteworthy than the degree of warmth is the lack of widespread autumn chill. For example, Minneapolis has yet to dip below 36°F as of Friday, October 28. That doesn’t look likely to happen before at least next weekend (November 5 - 6). In records going back to 1873, the latest Minneapolis has ever gone before seeing its first 35°F of the autumn is November 1, way back in 1931. The city’s latest first freeze was on Nov. 7, 1900.

The contiguous U.S. might still eke out some frigid weather later in November or December, especially if an emerging early-season split in the Northern Hemisphere’s stratospheric polar vortex works its way to lower levels over the next several weeks. The Weather Company’s latest seasonal outlook for North American industry clients, produced by Dr. Todd Crawford and colleagues, stated: “Recent evidence (expectation for blocking and enhanced Siberian high in November) is beginning to suggest that high-latitude blocking may be more likely than we originally thought, so colder risks beginning in December are now a concern.” For the time being, though, it looks like 2016 will maintain its current pace as the second-warmest year in U.S. history, giving 2012 a run for its money. And based on one index in particular--one that’s gotten little attention so far--this year is leaving all of its predecessors far behind.


Figure 1. Projected departures from average temperature (degrees C) on Thursday evening, November 3, 2016, based on output from the 00Z Friday run of the GFS model. Image credit: tropicaltidbits.com.

What happened to our record lows?
Because the contiguous U.S. is packed with so many long-term reporting stations, almost every year will produce thousands of record highs as well as record lows. The torrid year of 2012 produced more than 50,000 daily record highs, including 12,000 in just one month (March 2012, which gave us a historic and memorable “summer in March”). Yet 2012 also produced more than 10,000 daily record lows. Because the numbers on either side of this equation are always quite large, it’s the ratio of daily record highs to lows that points out most vividly where our nation’s climate has been heading in a world warmed by ever-increasing amounts of human-produced greenhouse gases.

Parallel with NOAA’s National Centers for Environmental Information, meteorologist Guy Walton has been compiling data on daily records for more than a decade. In 2009, Walton teamed up with Gerald Meehl and Claudia Tebaldi (National Center for Atmospheric Research) and several other colleagues to show that the ratio of highs to lows has been increasing decade by decade. In larger cities, the urban heat island effect is no doubt having an influence, but these relentless trends extend throughout rural and urban America. In the 1970s, the U.S. saw roughly 5 daily record lows for every 4 daily record highs. That ratio flipped in the 1980s, which produced about 6 highs for every 5 lows. By the 2000s, we were getting nearly twice as many daily record highs as lows (350,181 to 187,323). For the 2010s thus far, the ratio has climbed even higher: we’ve had about 2.2 times as many record highs as record lows. This is especially remarkable given that the years 2013 and 2014 both managed to buck the trend, scoring more daily record lows than highs. This year through October 25, the ratio is more than 5 to 1. That’s higher than in any full year on record.

Hiding in plain sight in the 2016 data is something even more astounding. Walton’s and NCEI’s numbers through October 25 show that this year has produced 20,847 U.S. daily record highs but a mere 3920 record lows. The latter may sound like a lot, but it’s a phenomenally low number. Since the mid-1920s, when the bulk of U.S. weather stations had accuмulated a meaningful 30-year history, the nation has notched at least 9000 daily record lows by the end of October in every single year. This year, we’re not even halfway to that point!


Figure 2. Number of daily record lows for the Jan-Oct. period, 1980 - 2016. Data for 2016 are through October 25. The number of record lows for 2016 sthus far (3920) is less than half of the next-lowest number of 9107 record lows that occurred from January to October 2012. Data courtesy Guy Walton and NOAA/NCEI.


Things could change dramatically between now and New Year’s Eve. It’s entirely possible for a single month to generate more than 10,000 daily record highs (as did November 1999) or lows (as did November 1991). Still, the take-home message is that 2016 so far is most impressive not for the number of its record-setting warm days but for its extreme lack of record-setting cold nights. This goes hand in hand with the high levels of atmospheric moisture that have kept many nights unusually warm in many areas, especially during the summer.

Seymour has come and gone
It never affected land, but Hurricane Seymour made a splash in East Pacific annals. Seymour both intensified and weakened with uncommon speed, going from a tropical storm to a Category 4 hurricane in 36 hours on Monday and Tuesday and then weakening from a Cat 4 to a tropical storm in just 30 hours on Wednesday and Thursday. The National Hurricane Center declared Seymour a post-tropical cyclone early Friday. Moisture from Seymour’s remnants will feed into a Pacific storm that will drench parts of central California this weekend.

There are no named tropical cyclones on Earth as of Friday morning, and none are expected through the weekend. A tropical wave parked in the northwest Caribbean is continuing to spawn showers and thunderstorms, but NHC gives it a near-zero chance of development over the next five days in its Friday morning Tropical Weather Outlook.

We’ll be back Monday with a new post. In the meantime, have a safe and fun Halloween weekend--and if you happen to be near Chicago’s Wrigley Field during the World Series game on Friday night, watch for wind-assisted baseballs flying out of the stadium!

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