Rare week-long stretch of 70-degree weather predicted for Washington, D.C.

This stretch of abnormally mild conditions could end up lasting two weeks, making history.

Already, highs in D.C. have hit at least 65 degrees for three days in a row. Computer models project we have 10 more such days to go, extending this streak to 13 days, which would be a record for November. The longest streak of 65-degree or warmer days in November is 11 from 1964.

Within this streak, we’re also expecting a series of days reaching 70 degrees or higher. D.C.’s longest uninterrupted stretch of 70-degree days in November is nine, set in 1979 and 1975. We probably won’t string together that many. But, if we get six, as computer models project, it would rank as November’s third-longest such streak. There’s an outside chance we could see as many as eight, which would mark November’s second-longest period of 70-degree days.

By itself, an early November day with a high in the mid-60s isn’t unusual, given average highs in the low 60s. But the duration of the upcoming mild pattern may prove exceptional.

The long-lasting warm pattern is the result of a persistent bulge or ridge in the jet stream developing over the eastern United States, which will promote air flow from the south. Temperatures across the entire eastern United States are predicted to be about 5 to 15 degrees above normal, averaged over the next 10 days. The western third of the United States, by contrast, will be stuck in a chilly, unsettled pattern, which can help quell fire prospects.

The warm start to November in the D.C. region is a departure from many recent years that, on balance, have been cool. Five of the past eight Novembers, including the past two, have been cooler than normal. It’s the only month of the year that in recent decades has averaged cooler than normal.

Although temperatures may cool slightly during the month’s second half, longer-range computer model forecasts suggest temperatures may, by and large, remain milder than normal through at least Nov. 20.

In the short term, “I don’t see anything to shake” the warm pattern said Capital Weather Gang contributor Matt Rogers, who specializes in long-range forecasting. “If there’s any sort of colder weather that’s coming, it would be in the bottom third of November.”

In some ways, this mild weather pattern fits the definition of “Indian summer,” which the National Weather Service describes as “an unseasonably warm period near the middle of autumn, usually following a substantial period of cool weather.” Indeed, the region saw five days in a row of colder-than-normal weather, including frost advisories and freeze warnings, between Friday and early Tuesday.

The warmer weather promises to extend D.C.’s “nice day” season, defined by the Capital Weather Gang as those days with highs between 65 and 85 and with low humidity, light winds and no rain.

Historically, such nice days are most likely in late September into early October before becoming scarce. November ranks seventh among the 12 months in the number of such days. But in 2020, we have the opportunity to pile up a slew of them.

Ian Livingston contributed to this report.

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