Typically-Comfy San Francisco Hits 100°F As West Coast Heat Wave Continues This Week

Hoowee. It hit 100°F at San Francisco International Airport on Tuesday, the warmest temperature ever recorded so early in the year. The heat wave baking the West Coast with unusually toasty temperatures for early June will continue through the end of the week, forcing some residents to deal with almost unbearable indoor temperatures.

Temperatures easily soared into the 100s as far north as northern California's Central Valley on Monday and Tuesday, with 90s at lower elevations through eastern Washington. Temperatures at 4:00 PM PDT on Monday are shown in the map at the top of this post. Even downtown San Francisco, which is typically rather cool given the influence of the chilly Pacific waters, made it all the way up to 97°F on Monday, breaking the station's record for June 10 by one degree.

Things didn't cool down much on Tuesday. Portland, Oregon, hit 95°F at 3:00 PM PDT on Tuesday, and temperatures were right up around 100°F again in the San Francisco Bay area. 

San Francisco's high on Monday was one of only seven times SFO Airport's temperature reached 100°F or warmer, and the earliest it's ever done so. Every other triple-digit reading at the city's airport occurred during the month of September, according to data pulled from xmACIS2 and professionally compiled on the lovely PowerPoint chart above.

Other record highs on Monday include 113°F in Thermal, CA; 105°F at Salinas Airport in Monterrey County, CA; 105°F in Stockton, CA; 104°F in El Cajon, CA; and 101°F in Redwood City, CA; and 101°F in Santa Rosa, CA. Many of the records broken in California, especially around the San Francisco area, have stood since at least 1994.

500mb height anomalies on Monday afternoon. Source: Tropical Tidbits

A large ridge of high pressure parked over western North America is responsible for the prolonged heat wave. Ridges tend to foster calm, hot weather—stronger and more anomalous ridges can bring about stronger and more anomalous heat waves. Models show the ridge sticking around for at least a couple more days, which means temperatures will be slow to cool down through the end of the week.

An animated loop of expected high temperatures across the western U.S. between Tuesday, June 11, and Friday, June 14.

The National Weather Service's forecast on Tuesday afternoon called for high temperatures at or near 100°F to persist across most of California's Central Valley through Friday. Things will progressively start to cool down at the coast in places like San Francisco and Los Angeles—the high in downtown San Francisco will only hit the mid-60s by the end of the week, but even inland the warmth won't be anywhere near as brutal as we saw on Monday.

It's bad enough to have to deal with hot temperatures when you're not used to them, but many homes and businesses in the western United States—especially near the coast—aren't equipped with air conditioning, which makes a days-long heat wave an uncomfortable and potentially dangerous prospect.

Heat is a compounding hazard. Enduring a successive period of extremely warm days and nights prevents the indoor temperature (and, back east, the humidity) from rebounding to a livable level. The longer a heat wave lasts, the more unlivable it becomes indoors. That's why so many people fall ill or die during long heat waves in low-income communities or climates where air conditioning isn't a standard in homes and businesses.

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