Heat Shifts to the Northwest After All-Time Record Heat Smothered the Southwest

Nick Wiltgen
Published: August 18,2015
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.
After much of last week and this past weekend featured brutally hot weather across the Southwest, now the heat is shifting north toward the Canadian border.

Forecast Highs

The heat has returned to the Pacific Northwest and will remain in place through midweek. Severeal daily record highs have either been tied or broken across Oregon and Washington so far on Monday and Tuesday.
Heat advisories have been issued through Wednesday in parts of northwest Oregon and southwest Washington with highs up to 20 degrees above average expected in western parts of Oregon and Washington again on Wednesday.
(FORECAST: Seattle | Portland | Boise)
Portland could easily top out in the 90s on Wednesday. This would give the Portland airport its record twenty-fifth day with highs in the 90s in a calendar year.
On Tuesday, Portand smashed their daily record high temperature by three degrees when they topped out at 96 degrees. The previous reocrd was 93 degrees, set back in 1946.
Daily record highs will be threatened in the following cities (current record in parentheses):
Wednesday: Seattle (88 degrees); Salem, Oregon (99 degrees); Portland (97 degrees); Eugene, Oregon (101 degrees)
Cooler air will arrive late week, dropping temperatures closer to average.
Along with the heat, there has been an increased threat of wildfires across portions of the Northwest as well. Red flag warnings remain in place through at least Wednesday afternoon for a large portion of Washington. Adjacent portions of Idaho and Oregon are also under red flag warnings.
(MORE: Latest on Western Wildfires)

Southwest: August Records Challenged

Actual high temperatures measured in selected locations Aug. 14-16, 2015, along with the all-time August record highs for each place.

Observed low temperatures for selected locations in the Southwest from Aug. 14-16, 2015. It was the first time Phoenix has ever recorded three consecutive days of lows at or above 93ºF (34ºC).

At least one major heat record has 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 Friday, Saturday and Sunday 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 Monday morning and into the upper 80s on Tuesday morning. 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.

Three-Day Forecast

Phoenix's 117-degree high Friday 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 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. Sunday and Monday the high topped out at 122 degrees in Death Valley.

Current Temperatures

The lower elevations of the Las Vegas area and parts of the Colorado River Valley are under excessive heat warnings through Wednesday.  If you are in any of these areas, take precautions against the heat. Drink plenty of water, stay in the shade as much as possible, and take a break now and then in an air-conditioned building.
(FORECAST: Tucson | Las Vegas | San Diego)
And it's not just the Southwest that's been feeling the heat. Along the central coast of California, Santa Cruz topped out at 101 degrees Saturday, crushing 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 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.
(FORECAST: Downtown L.A. | LAX Airport | Encino)
Excessive heat warnings for inland areas near Los Angeles and San Diego have now expired, as a cooling trend began Monday.
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.
MORE: Western Wildfires, July 31 - Aug. 11, 2015