Published: August 16,2015
When the National Weather Service issues "excessive heat warnings" for the hottest region of the country, you know it's hot. And when Phoenix ties its all-time August record high, you know it's really hot.
Excessive heat warnings have been in place for more than 14 million Americans in three states since Friday. The bubble of high pressure responsible for the last week's heat wave in Texas and Louisiana has shifted westward to Arizona, putting the Desert Southwest in the hot seat.
And it's not just the Southwest that's feeling the heat. Heat advisories are in effect for parts of west-central California, including the San Francisco Bay Area. Santa Cruz, California, topped out at 101 degrees Saturday, which crushes its daily record high for Aug. 15 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 Saturday. Sunday's high reached at least 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.
Southwest: August Records Challenged
Observed High Temperatures
At least one major heat record has already been established in this heat wave. On Friday, 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, Friday's 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 Saturday, which is a new daily record for Aug. 15 (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 both Friday and Saturday were a torrid 93 degrees. Sunday's morning low was also 93, and if that figure holds through midnight local time, it will be the first time Phoenix has ever recorded three consecutive calendar days without falling below 93.
In a way, to call this a "pressure cooker" could be considered more than just a metaphor. The high-pressure zone is literally exerting 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.
Three-Day Forecast
Death Valley National Park, already the world recordholder for highest official temperature, hit 122 degrees Friday and 123 Saturday, easily clinching the nation's hot spot both days. Saturday's reading was the highest August temperature in Death Valley since 2012.
In all, at least twelve daily record highs were broken on Saturday with six additional locations tying their record highs for the date.
Current Temperatures
(FORECAST: Tucson | Las Vegas | San Diego)
Southern California Temperatures
For cooling over the weekend, Angelenos had to head to the beach. Highs Saturday soared to 107 in the Woodland Hills, Van Nuys and Chatsworth neighborhoods of the city, while Los Angeles International Airport only hit 81, and the famous pier in the neighboring city of Santa Monica only hit 73.
Highs in the inland valleys will cool into the 90s and eventually 80s this week. More importantly, overnight lows will recede back into the lower 60s, allowing for a break in the warmth at night.
The Weather Channel smartphone app and weather.com give you forecasts down to neighborhood and zip-code level, so make sure you check the forecast for your specific area of interest to get the forecast most relevant to your plans.
(FORECAST: Downtown L.A. | LAX Airport | Encino)
Northwest: Heat Relief
A cold front has swept through the Northwest and has knocked down the heat in that region.(FORECAST: Seattle | Portland | Boise)
It was welcome relief particularly in Montana, where some places had a four-day run of triple-digit heat ahead of the front. Glasgow, Montana, reached 105 degrees Saturday, its hottest day since July 2007 and its hottest August day since 1983.
Unfortunately, this friendly front brought along some bad company Friday into Saturday – a punch of strong winds in the middle and upper levels of the atmosphere. Some of this wind came to ground level, making for windy conditions. Those have subsided as the cold front has moved well east of the region.
Cooler air has settled into the region and will stick around for a few days.
(FORECAST: Billings | Casper)
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