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D.C. is nearing a record for 80-degree days in 2018, with more ahead

Is it October or August? A hazy sunrise Thursday along the Potomac. Highs were expected to soar well into the 80s to perhaps near 90. (Carol Jean Stalun via Flickr)

High temperatures in the D.C. area, according to historical averages, should now be in the low 70s and falling another degree or so every few days. However, today’s anticipated high in the mid- to upper 80s, and the forecast for more to come, seems to be fitting more recent weather trends.

With 131 days at or above 80 degrees so far in 2018, the city is already running 14 days above the average of 117 for such daily temperatures. And we’re now just a handful of days away from setting a new record: The forecast says we’ll end up right near the top mark of 136 by the time cooler air arrives in a week to 10 days.

Each day the District reaches 80 or higher pushes the city closer to the top of the leader board. The 131 so far this year ranks second-most year to date to 132, in 2010 and 1970.

Even if today was the last 80-degree-or-higher day in the city — and it won’t be — this year would finish in a tie with the fourth-most such days in a year. The top value of 136 in a calendar year, set in 2007 and 1970, is certainly in play, given current forecasts. It could be a photo finish.

It’s now also the case that five of the top six years for 80 degree days in the District have come since 2007, and this is in a record dating to 1872. The top 20 years for 80 degree days are dominated by the 2000s and 2010s, which make up half.

Considering that the annual average in these days has risen from less than 100 in the 1800s to around 120 today, this is clearly a metric with an unmistakable upward trend. Both urbanization and climate warming from rising greenhouse gas concentrations are the likely cause.

It’s quite possible that Washington will, in the same year, set a record for most days with 80-plus highs and 70-plus lows. Recall in September, we reported the city had already set a record for the most instances of low temperatures of at least 70 degrees.

How unusual is 80 degree weather in October?

Even as we pile up more 80 degree days, it’s possible this October warm spell may not set many records. While it will be notable for its duration, it turns out that 80-degree and even 90-degree weather isn’t terribly uncommon — especially in the first half of the month.

On average, our last 80-degree day comes around Oct. 16. This year’s bout of summerlike weather is coming squarely before that, at least as far as we can tell. It’s too soon to know whether we’ll see any warm spells in the second half of the month or into November.

Looking at the 2010s, the earliest final 80-degree (or warmer) day came Oct. 6 in 2013, when it was 91 degrees. The latest 80 degree day was Nov. 6 in 2015. The long-term record for the latest 80-degree day is Nov. 18, way back in 1921.

Temperatures in the 90s in early October is somewhat more rare, but we’ve seen some recent instances, and it could happen this year, too. The most recent October 90 occurred in 2013 (which, as noted earlier, was the last time it was above 80 degrees that year). If we hit 90 on Oct. 9 or later, it would rank among the top 10 percent of latest cases on record. The latest 90-degree day on record occurred Oct. 11, 1919.

While 80-degree or even 90-degree warmth this late into the year isn’t that uncommon, the numbers of 80s we are expecting to see is indeed something.

October averages between three and four days of 80 degrees or above. So far, we’ve seen four (including today), and there are likely at least four to six more to go. Getting to nine 80 degree days this month would mark a tie for the fifth-most on record. In 2007, the District. saw an incredible 15 days of 80 degrees or higher, which is the most witnessed in modern history for the region.