Topline:
The National Weather Service has issued extreme heat warnings for much of Southern California from Tuesday morning through Friday evening.
The details: Highs in downtown Los Angeles are expected to reach 100 degrees over the next few days. The warmest parts of inland valleys, such as Santa Clarita, are expected to get up to 112. L.A. County beaches will hit the high 80s. Temperatures are expected to peak between Tuesday and Thursday and cool down slightly over the weekend, although they will stay above normal.
Driving the heat: A high pressure system over the southwestern U.S. is largely to blame for this heat wave and others this summer. At the same time, offshore winds are blocking the ocean’s cooling effect.
Smog concerns: Air quality officials have issued an advisory for high ozone pollution this week, caused in part by the heatwave.
Read on … for more details on this week’s forecast.
There unfortunately isn’t much respite in sight for heat-weary Southern Californians.
Forecasters say this week’s heat wave is likely to be the hottest so far this summer. Extreme heat warnings will be in effect from the National Weather Service for almost the entire region from Tuesday morning through Friday evening.
Temperatures will peak between Tuesday and Thursday.
Highs in downtown Los Angeles are expected to reach around 100 degrees, and the warmest inland valleys will get up to 112. L.A. County beaches will hit the high 80s.
Forecasters have also issued Red Flag Warnings for the interior mountains and foothills of Los Angeles, Ventura and Santa Barbara counties. Gusty winds and low humidity at higher elevations mean fires could spark and spread quickly.
At lower elevations, humidity continues to make the heat feel more sweltering and make it harder to cool down, especially at night. Nighttime temperatures will only get down to the 70s in most places, including along the coast.
A slight cooldown is expected this weekend, though forecasters say temperatures will stay above normal into next week.
The extreme heat this week poses an especially high risk of heat-related illness for people over 65, young children, people who work or spend a lot of time outside and those without access to air conditioning.
Staying safe in the heat
Hydrate
- Don't wait until you're thirsty to drink water or electrolyte replacements.
- Drink cool water, not extremely cold water (which can cause cramps).
- Avoid sweetened drinks, caffeine and alcohol.
Protect pets
- Never leave a pet or animal in a garage.
- Never leave a pet or animal in a vehicle.
- Never leave a pet or animal in the sun.
- Provide shade.
- Provide clean drinking water.
Protect people
- Check in frequently with family, friends and neighbors.
- Offer assistance or rides to those who are sick or have limited access to transportation.
- And give extra attention to people most at risk, including:
- Elderly people (65 years and older).
- Infants.
- Young children.
- People with chronic medical conditions.
- People with mental illness.
- People taking certain medications (i.e.: "If your doctor generally limits the amount of fluid you drink or has you on water pills, ask how much you should drink while the weather is hot," the CDC recommends).
Driving the heat
Several factors are behind this week’s heat wave, many of which have also been behind the rest of this summer’s consistently hot weather.
The main driver is a high pressure air system hovering over the southwestern U.S., trapping warm air, compressing it and warming it further, and blocking cooler air from entering the region.
Offshore winds are also pushing warm inland air toward the coast, preventing cooler onshore winds from blowing inland.
“That blocks our natural air conditioning off the ocean from coming in as early as it normally does,” said Weather Service meteorologist Mike Wofford. “So as long as that cool air stays offshore, it heats up on land.”
The offshore winds are not strong enough, however, to significantly dry out the air in the L.A. Basin and cut down on the humidity.
“That's probably going to be around for the whole summer because you’ve got all this warm ocean water that's feeding into that,” Wofford said.
Warmer seawater evaporates faster, adding to moisture in the air and increasing humidity across the region, especially along the coasts.
Making sense of heat forecasts
Southern Californians are no strangers to hot weather in the summer, but heat waves are getting hotter, longer and more frequent as the climate changes.
So you should know the words forecasters use to describe these weather events — and the risks they pose.
- Heat advisory: Advisories are issued when temperatures are expected to be hot enough to cause discomfort and potentially lead to heat-related illnesses, especially for more vulnerable populations like young children and the elderly.
- Extreme heat watch: Watches are essentially forecasts for upcoming periods of extreme heat. Forecasters say heat watches often cover wide areas and will be revised into more focused warnings and advisories as conditions become clearer over time. Watches are a good time to prepare for extreme heat.
- Extreme heat warning: Warnings are issued when heat levels are or will likely become extremely dangerous. Under extreme heat warnings, it's a good idea to avoid strenuous outdoor activity, stay hydrated and help loved ones and pets stay cool.
Learn more >>
Air quality warnings
Along with the heat this week, many Southern Californians also have smog to worry about.
The South Coast Air Quality Management District issued an ozone advisory on Monday for inland areas of Los Angeles and Orange counties, much of Riverside County and parts of San Bernardino County. It will remain in effect through Friday evening.
The multi-day smog event is in part driven by the heatwave.
Officials say ozone pollution may reach unhealthy levels or higher in the Santa Clarita Valley, parts of the San Gabriel and San Bernardino valleys, and portions of the San Bernardino Mountains.
Under unhealthy levels, it’s possible for anyone to experience adverse health effects like difficulty breathing and throat irritation. Sensitive populations could experience more serious effects.
Levels are expected to be unhealthy for sensitive groups in the San Fernando Valley, Perris Valley, Mission Viejo, Lake Elsinore, Corona, Hemet, Riverside and Pasadena.
Officials advise certain vulnerable groups — including people with heart or lung disease, those with asthma, pregnant women, children and people over 65 — to limit their time outdoors.
Officials predict that ozone levels will be lower along the coast.
