Since Saturday, the days have simmered and nights just haven’t cooled off much. Quietly, a heat wave of historic significance has blossomed in Washington.

The temperature hasn’t been below 80 degrees since 6 a.m. Saturday (when it was 79). D.C. has posted 124 straight hours of temperatures 80 degrees or higher, encompassing more than five consecutive days (7 a.m. Saturday to 11 a.m. Thursday).

This period at or above 80 degrees is the third longest in weather records dating to 1872. The longest period on record, which occurred July 15-21, 2013, spanned 138 hours. The second longest such period, 128 hours, occurred July 20 to 25 in 2011.

The current period will pass the 2011 period Thursday afternoon and move into second place.

For this year’s period to top 2013 and attain the No. 1 position, it must remain at least 80 degrees through 2 a.m. Friday (or until 1 a.m. to tie it). Because the region is expecting widespread thunderstorms late Thursday afternoon and evening, this may prove difficult. Such storms can cool the air, so there’s a realistic chance temperatures drop back into the upper 70s. It’s going to be close.

Capital Weather Gang’s Ian Livingston points out that if you evaluate the longest periods during which the temperature has remained 79 degrees or higher (instead of 80 degrees), 2016 has accumulated 148 hours (through 11 a.m.), which is the most on record (above 2013’s 140 hours).

During this five-day-plus stretch of steamy weather, D.C. has set or tied records for warmest low temperature three times:

  • Monday’s low of 81 degrees broke the old record warmest reading of 79 from 1965.
  • Tuesday’s low of 80 degrees broke the old record warmest reading of 79 from 1987.
  • Wednesday’s low of 81 degrees tied the record warmest reading from 1930.

Today’s low of 81 degrees (so far) would break the record warmest reading of 80 from 1949 if the temperature does not fall to 80 or below before midnight.

Occurrences of low temperatures of 80 degrees or higher have increased dramatically in recent decades. There were only 26 such instances from 1872 to 1999, but there have been 30 since (from 2000 to 2016), in one-fifth of the amount of time.

In addition to the warm overnight temperature over the past several days, the string of scorching daytime highs in D.C. is also historically notable.

Highs over the past six days have all reached at least 95 degrees and at least 97 in the past five days: 95 (Friday), 98 (Saturday), 97 (Sunday), 100 (Monday), 98 (Tuesday) and 97 (Wednesday).

The six straight days of at least 95 degrees ties for the 10th longest streak on record, while the five straight days of at least 97 degrees ties for the fourth longest such streak.

The longest streak of 95 or hotter days is 11 in 2012, while the longest stretch of at least 97 degrees is seven days in 1953.

It’s not out of the question for D.C. to tack on a seventh straight 95-degree day today — which would put this year’s streak in a tie for fifth longest. It probably won’t hit 97 degrees.

By Friday, highs are forecast to be in the 80s to near 90, well below these thresholds of more extreme heat.

Ian Livingston contributed to this post.