Excessive heat baked the Desert Southwest in mid-August 2015, sending Phoenix to a tie of its all-time August record high. The hot temperatures also affected parts of southern Nevada, California and the Pacific Northwest.

Southwest: August Records Challenged

At least one major heat record was established in this heat wave. On Aug. 14, Phoenix Sky Harbor International Airport recorded a high of 117 degrees, tying the Arizona capital's all-time record high for the month of August previously set Aug. 26, 2011. Like that date, the low was 93, so it also tied for Phoenix's warmest daily mean temperature on record for the month of August.

Phoenix topped out at 115 degrees on Aug. 15, which is a new daily record (previous record was 112 degrees in 1992).

(FORECAST: Phoenix | Scottsdale | Mesa )

The health dangers of heat waves are not just a function of high temperatures, though. Very warm overnight lows can cause problems for anyone living without access to air conditioning, or for those who cannot afford the electricity required to take full advantage of their AC.

In Phoenix, the lows Aug. 14-16 were a torrid 93 degrees. This is the first time Phoenix has ever recorded three consecutive calendar days without falling below 93. The mercury fell to 91 on the morning of Aug. 17 and into the upper 80s on the morening of Aug. 18. Phoenix's record for most consecutive lows in the 90s is seven straight days from Aug. 7 through Aug. 13, 2012.

In a way, to call this a "pressure cooker" could be considered more than just a metaphor. The high-pressure zone has literally exerted a downward influence on the air over the Southwest. Since clouds and rainfall require rising air motions (not to mention adequate moisture), large-scale sinking air tends to prevent or inhibit precipitation from developing.

That means more sunshine, which in turn, means more heat. In addition, the air mass itself is warmer in the first place, so the sun is heating up air that's already toasty to start with.

Relative to historical norms, the epicenter of the heat has been over central and southern Arizona and southeastern California.

Phoenix's 117-degree high Aug. 14 made it the hottest day of 2015, surpassing the 115 recorded June 18. Of the past 20 years (1995 through 2014), Phoenix's annual high temperature has only occurred in August three times: 2012, 2004 and 1999. In 2004 and 1999 August shared the crown with July.

Death Valley National Park, already the world record holder for highest official temperature, hit 122 degrees Aug. 14 and 123 Aug. 15, easily clinching the nation's hot spot both days. The Aug. 15 reading was the highest August temperature in Death Valley since 2012. Aug. 16-17 the high topped out at 122 degrees in Death Valley.

(FORECAST: Tucson | Las Vegas | San Diego )

And it's not just the Southwest that felt the heat. Along the central coast of California, Santa Cruz topped out at 101 degrees Aug. 15, crushing its daily record high for that date by 13 degrees. Weather records in Santa Cruz go back 120 years, which makes the margin by which this record was broken very impressive. It is also only the sixth time in those 120 years that Santa Cruz has recorded a triple-digit daily high temperature in the month of August.

A daily record high of 92 degrees was also set at San Francisco International Airport on Aug. 15. On Aug. 16 the high reached 90 at SFO, breaking another daily record (86 on Aug. 16, 1960). It's only the fourth time SFO has had back-to-back 90-degree days in August since records began there in 1945, and only the fifth time it's had two 90-degree days at all in August. San Francisco's airport has never had three 90-degree August days in the same year, whether consecutive or not.

Northwest Heat: Portland Sets Record for Most 90s

Portland easily topped out in the 90s Aug. 18-19. This gave Portland's airport its record 26th day with highs in the 90s in a calendar year. This breaks the previous record of 24 days, set back in 2009 and records for the airport date back to 1940.

To the north, Seattle, Washington, just missed reaching the 90-degree mark on Aug. 19, but their high of 89 degrees was enough to break the daily record of 88 degrees, set back in 1967.

MORE ON WEATHER.COM: Western Wildfires, July 31 - Aug. 11, 2015