Dangerous, oppressive, stifling. These words were repeatedly used to describe the historic heat wave that slowly engulfed the D.C. area by the middle of last week and earned the name “Sweat Ceiling”.

The latest round of high heat and humidity began one week ago, with temperatures exceeding 90 degrees for the past seven days at all three area airports. While temperatures generally remained in the low-to-mid 90s through Wednesday (July 20), humidity levels crept steadily upwards that evening, signaling the arrival of the very hot and humid air mass spreading eastwards from the Plains.

Thursday through Saturday (July 21-23) featured the core of the heat wave, with high temperatures of 99-106 during that span.

July 1893/7393/6895/70
July 1997/7993/7395/74
July 2094/7794/75*93/72
July 2199/80100/75100/77
July 22102/83*105**/76*106*/81*
July 23102*/84**99*/76*102*/78
July 2497/84**94/7798/78

High and low temperatures July 18-24, 2011 at Reagan National (DCA), Dulles (IAD), and BWI Airports. One star indicates record. Two stars indicate all-time record.

Here’s a summary of the records and/or near records that were set during this period:

July 20:

* IAD ties 1994 record for warmest low for date of 75 .

July 21:

* DCA’s dew point - a measure of humidity - climbs to 81 degrees at 9 p.m., tying several other dates for second highest on record all-time (dew point records date back to 1962).

July 22:

* IAD hits 105, crushing old daily record of 98 from 1998 and besting previous all-time (since 1963) record of 104 (from July 16, 1988 and August 20, 1983). BWI sets daily record of 106 (blazing past old record of 101 from 1957), which is second highest all-time (since 1871). DCA’s record high of 102 is one shy of record for date (103 from 1926) and four shy of the all-time hottest day (106 from July 20, 1930). (More info.)

* Record warmest daily low temperature of 83 set at DCA (previous 81, 1987) and 76 at IAD (previous 75, 1969). BWI ties 1885 daily record for warmest low of 81. DCA’s 83 ties for second warmest all-time (since 1871). (More info.)

* DCA heat index reaches 121 at 3 p.m., second highest known level since 122 on July 16, 1980.

July 23:

* DCA sets daily record of 102, breaking record of 101 from 1991. BWI also reaches 102, tying record for date from 1991. IAD hits 99, tying daily record also from 1991.

* DCA sets daily record for warmest low of 84 (breaking old record of 81 from 1978), which ties the all-time (since 1871) warmest low from July 16, 1983. IAD falls to 76, a daily record for warmest low (previous record 73, from July 23, 1978).

July 24:

* DCA sets daily record for warmest low of 84 (breaking 2010 record by three degrees) and ties the all-time (since 1871) mark from July 16, 1983 and the previous day (July 23, 2011).

* Capital Climate notes: “for the first time in records which date back 140 years to 1871, the Washington temperature failed to go below 84° for over 48 consecutive hours.”

Also notable:

* Reagan National has now had back-to-back 100-days in two straight years (last year was July 6-7).

* The region experienced two code red days air quality days (unhealthy for the general population) on July 22 and 23

* DCA’s streak of four straight days with lows at or above 80 is the most on record. Since this morning’s (7/25) low only fell to 80, if it holds, it would extend the record to five days. In addition, the low of 80 would set another daily record for warmest low, exceeding the 79 from 1965. For comparison, D.C. had three days total with lows of 80+ from 1871 to 1930.

* DCA’s temperature has been at least 80 since 8 am on Wednesday, July 20... a record 125 hours and counting...

High temperatures in the 90s are not going anywhere soon. And believe it or not, after July 2010 tied the record for the hottest month ever recorded at National Airport averaging 83.1 degrees, July 2011 is now on pace to break the tie – with an average monthly temperature of 83.6 degrees recorded through yesterday. There is still another week left to see if D.C. breaks another warmth record, but all of the above records make it clear how we got to this point.