The weather in the West has gone off the rails. Since late in the past week, the blistering heat has set scores of high-temperature records. The heat has fueled violent thunderstorms unleashing a barrage of lightning strikes, igniting a rash of fires. Lightning even filled the sky over the San Francisco Bay area on Sunday and Monday, where such displays are rare.
The extreme weather stems from a massive, unusually intense heat dome over the Southwest. It developed late in the past week and is now near peak intensity. It is forecast to hold in place for at least another week, although its strength will gradually ease.
Excessive heat warnings and heat advisories smother the western United States, affecting much of California (except for the high elevations of the Sierra Nevada range); all of Nevada; much of western and southern Arizona, including Phoenix; western Utah, including Salt Lake City; central and eastern Oregon and Washington; and large parts of Idaho and Montana, all the way to the Canadian border. Over 56 million Americans are under some sort of heat alert.
Heat is the leading cause of the weather-related deaths in the United States in many years. “Long duration heat spells like this one can be extremely dangerous, be sure to limit your outdoor exposure and stay hydrated!” tweeted the National Weather Service forecast office serving Las Vegas, which is under an excessive-heat warning through at least Wednesday.
Since Friday, scores of long-standing heat records have fallen. Several of these records have not only met or exceeded previous marks for the day they occurred but also for the entire month of August. Some of the August records include:
- Phoenix hit 117 degrees Friday, tying its highest temperature during the month.
- Oakland hit 100 degrees Saturday for the first time on record during August.
- Needles, in California’s southeastern desert, set an August record of 123 on Saturday.
- Sacramento set an August record of 112 degrees Sunday.
The searing 130-degree high temperature in Death Valley on Sunday has captured international attention. If confirmed, it will become the highest temperature measured on the planet during August and the third-hottest in any month. It would also be the highest temperature observed on Earth since at least 1931. The only hotter two temperature measurements prior to that are disputed by some experts.
Death Valley could flirt with 130 degrees again Monday afternoon. In fact, it is forecast to see highs at or above its previous August record of 127 degrees through Wednesday. Highs of at least 124 degrees are forecast through Sunday.
While not as extreme as Death Valley, the heat in Phoenix has also been unforgiving. After posting its hottest month on record in July, it has hit at least 110 degrees for five straight days. Highs are forecast to remain near or above 110 degrees for the entire week. It has reached at least 110 degrees on 40 days in 2020, crushing the previous record of 33 such instances in 2011.
In California, the heat resulted in scores of record highs over the weekend including around Los Angeles, the San Francisco Bay area and Sacramento. Early Sunday morning, a bizarre “heat burst” raised the temperature 20 degrees in two hours in Fairfield, about 40 miles northeast of San Francisco. The temperature shot from around 80 to 100 degrees in the hours around sunrise.
Because of the demand for cooling, California endured rolling power outages Friday. Utilities urged residents to conserve energy to reduce the chance of additional blackouts.
“Conservation is critical to help reduce the need for the California Independent System Operator (CAISO) to direct the state’s utilities, including PG&E, to implement rotating outages in order to reduce load,” wrote PG&E on its website Monday. “With the weather forecasted to be even hotter, PG&E urges customers to be prepared for power outages.”
Fueled by the heat, a round of booming thunderstorms that produced a spectacular lightning show early Sunday morning awakened residents in the Bay Area. A surge of moisture ejecting north from former Tropical Storm Fausto near the Baja Peninsula contributed to the rare summertime storms. The storms ignited a number of new wildfires through their pinpoint lightning strikes.
The National Weather Service in San Francisco issued an unusually large severe thunderstorm warning that covered more than 7,000 square miles from Monterey Bay to the Bay Area and north into Napa Valley. The office warned of “erratic outflow wind gusts of 50 to 70 mph wind gusts, [and] frequent lightning.” The warning, the largest ever issued by that office, was six times larger than the state of Rhode Island.
“This 20 year forecaster cant recall such a widespread [thunderstorm] event on the heels of such a heat wave,” wrote one meteorologist in the office forecast discussion late Sunday.
The storms were preceded by an extraordinary roll cloud, marking the leading edge of cool air associated with the storms working up the Santa Cruz Coast.
A second round of thunderstorms occurred early Monday morning but with considerably fewer lightning strikes. That’s because moisture at the mid-levels of the atmosphere was scant in comparison to Saturday night. Concern was growing that “dry thunderstorms” could spark lightning strikes with little to no rainfall to quell the flames.
“Any thunderstorms that do develop will move quickly with lightning strikes outpacing any (unlikely) wetting rains at the surface,” the National Weather Service wrote.
More thunderstorms, including some dry thunderstorms, were expected throughout the day Monday. One webcam revealed four small fires ignited by lightning in one area Monday morning.
Extreme fire behavior
The anomalously hot and dry conditions have acted as a breeding ground for wildfire growth, supporting extreme fire behavior and making the concerns surrounding dry lightning that much more pressing.
National Weather Service offices in California blanketed much of the state in red flag warnings to account for fire danger exacerbated by the heat wave.
Hazards include a “high probability of fire starts with any lightning,” according to the National Weather Service in Sacramento. “Rapid spread of fire [is] possible depending on terrain and local wind conditions.”
Even after any thunderstorms pass, persistent hot, dry conditions will sap vegetation of moisture and litter the ground with fuel ripe for fire growth. A number of other wildfires continued to rage Monday, taking advantage of the parched conditions to blaze at full fury.
On Saturday, the rapidly expanding Loyalton Fire in Lassen County, Calif., between Reno, Nev., and Lake Tahoe, produced a barrage of extreme fire tornadoes that prompted a first of its kind “fire tornado warning.”
The souped-up version of a tornado warning mentioned the potential of fire tornadoes and 60-mph winds, cautioning “this is [an] extremely dangerous situation for fire fighters.”
The Loyalton Fire had burned some 36,295 acres as of Monday morning, and was only 5 percent contained.
Farther south in Southern California, the Lake Fire was burning in the mountains northwest of Los Angeles. It had claimed more than 18,300 acres by Sunday night, and was still raging to kick off the workweek. The fire was 12 percent contained.
An extreme heat dome, likely made more intense by climate change
The exceptionally hot and dry conditions are made possible by a significant ridge of high pressure, colloquially referred to as a “heat dome.” Air inside the system sinks and warms, while drying out and eradicating any widespread shots of rainfall.
On weather maps, a rare number appeared as a testament to how significant the heat dome is: 600. That describes the height in dekameters, or tens of meters, that the halfway point of the atmosphere’s mass is above the surface.
When air warms, it expands. When it cools, a volume of air shrinks. An air mass this hot expands a lot, causing a column of air to grow and raising the atmosphere’s halfway point. With this particular system, that level is 6,000 meters — or about 19,700 feet — above the surface.
This level “represents a threshold that is coincident with record heat over the Western United States,” wrote Ryan Maue, a meteorologist who operates the website weathermodels.com, in a Twitter message.
Instances of heat domes exceeding this 6,000-meter level used to be rare but have increased dramatically in recent years. Maue examined data back to 1958 and found almost all of the high-powered heat domes have occurred since 1983 — with the overwhelming majority of them occurring since 1990.
“[T]he 6000-meter club “heat domes” are certainly becoming more frequent b/c of climate change, now a nearly annual occurrence,” he wrote in a Twitter message.
Scientists have found the intensity, duration and frequency of heat waves worldwide are increasing because of human-caused climate change. A 2019 study found the planet has entered a “new climate regime” with “extraordinary” heat waves that global warming is worsening.