On average, Washington hits 100 about once every three years, although it did so a remarkable 17 times between summers of 2010 to 2012 and four times last summer.

Factor in the humidity, and it will feel closer to 100 to 105 during the upcoming three-day span. In fact, on Thursday, the National Weather Service indicates there’s a 42 percent chance the maximum heat index exceeds 105 degrees. The Weather Service issues a heat advisory when the heat index is reasonably likely to hit 105 degrees in Washington, so prospects of an advisory issuance that day are pretty good.

Here are the reasonable expectations for maximum afternoon temperatures and heat index values Tuesday through Thursday in Washington:

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Tuesday: 97, heat index 104

Wednesday: 97, heat index 104

Thursday: 99, heat index 105

Note that our cooler suburbs should expect to see temperatures several degrees lower, with highs mostly in the mid-90s on these days.

Very muggy nights will complement the brutally hot afternoons. Low temperatures only in the upper 70s Wednesday and Thursday in the District may well challenge records. The existing record high minimum temperatures in D.C. on those days are 77 (set in 2011) and 78 degrees (set in 1993, 1992 and 1981).

The extreme heat is the result of a heat dome, or an area of high pressure at high altitudes that is forecast to sit over the Southeast through the middle of the week.

A cold front crossing the region Thursday night into Friday will kick it out to sea, putting an end to the punishing combination of heat and humidity. The arrival of drier, milder air will be most apparent Saturday.

Records

For reference, here are the record high maximum and minimum temperatures at our three local observing sites Tuesday through Thursday; those in bold have the best chance to be challenged:

Washington

Tuesday: High max: 99 (set in 1988, 1987 and 1936) | High min: 79 (set in 1989)

Wednesday: High max: 99 (set in 1908) | High min: 77 (set in 2011)

Thursday: High max: 100 (set in 1954) | High min: 78 (set in 1993, 1992 and 1981)

Dulles

Tuesday: High max: 98 (set in 1998) | High min: 74 (set in 1989)

Wednesday: High max: 97 (set in 1996) | High min: 72 (set in 2006)

Thursday: High max: 97 (set in 1986 and 1966) | High min: 74 (set in 2016)

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