The combination of punishing temperatures to 100-105 and high humidity levels has prompted the National Weather Service to issue an excessive heat warning from 11 a.m. to 10 p.m. Saturday - its most serious heat alert. Heat indices may exceed 110 in the afternoon. In addition, air quality is forecast to be code red, unhealthy for the general population.

Through Tonight: Mostly clear skies but uncomfortably warm and humid. Lows are only near 80 in the city with low-to-mid 70s in the cooler suburbs.

Saturday: Mostly sunny and dangerously hot. Highs reach 100-105, with an outside chance of touching 106, D.C.’s all-time hottest temperature. There is a strong chance we reach 102 degrees, the daily record. Air quality is forecast to be in the unhealthy range which means everyone should avoid prolonged or heavy exertion outdoors. If you must spend long periods of time outside, continuously hydrate and take breaks in an air-conditioned environment.

More mugginess Saturday night, with lows again only from near 80 downtown to the low-to-mid 70s in the suburbs.

Sunday: One last oppressively hot and humid day, with highs in the upper 90s to near 100. A cold front promises to break the heat, but it is likely to trigger thunderstorms some of which may be severe.

See Camden Walker’s forecast through the weekend. And if you haven’t already, join us on Facebook and follow us on Twitter. For related traffic news, check out Dr. Gridlock.

Chicago heat: Believe it or not, the Windy City has had more 90 degree days this summer than D.C. It’s current count is 23 - compared to our 19. It’s already blown by its summer average of 17. WGN’s Tom Skilling says the start of July is the hottest there in 101 years. And WGN’s Tim McGill notes the recent heat is comparable if not more intense than the deadly 1995 heat wave, which claimed more than 600 lives.