Heat and drought shape Southern California’s summer outlook

Memorial Day, the unofficial start of summer, is Monday. What’s in store for the upcoming season of Southern California beach days and barbecues?

For starters, it will dry. That’s not only because California’s Mediterranean climate means rain falls mostly on a few wet winter months, but because the state is in its third year of drought.

This year, after an unusually wet December, California experienced its driest January, February, and March on record – some of the months the state is expected to collect nearly all of its crops. rain. California’s rainfall often occurs during a handful of winter storms. The state has an average of seven strongly atmospheric rivers in the water year from October to September, according to the Center for Western Weather and Extreme Water at the Scripps Institution of Oceanography in San Diego. The state started the 2021-22 water year with a river with a special atmosphere on October 28, but then only five rivers were strong all winter, making it the third year in a row to be active. atmospheric rivers below normal.

Warm days melt the snow that has been stored in the mountains early in the season. The snow and ice layers in the Sierra often serve as cold storage for a large portion of the state’s water supply. It gradually melts during spring and summer, supplying rivers and reservoirs, supplying cities and farms. By April 1, the amount of snow and ice had dropped to just 38% of the average. Major reservoirs statewide are at 76% of average this week, with long hot summer months still ahead.

Timeline of drought in California since 2000.

For the last two decades, California has been in a dry state.

(Paul Duginski / Los Angeles Times)

After three dry months, April’s rainfall provided Northern California with some relief, but that spring’s rainfall wasn’t as much as needed to alleviate the prolonged drought.

According to the US Drought Monitor, extreme drought continues to expand. A timeline of the percentage of California experiencing drought since 2000 illustrates the longstanding view that the state has been in drought, with a few intermittent wet years, for more than two decades. Scientists say this is the driest 22-year period in at least 1,200 years.

During those 22 years, the longest period when the state was besieged by moderate to exceptional drought lasted 376 weeks, from December 27, 2011 to March 5, 2019. The most intense week was at the end of July 2014, when 58.41% of California’s land was classified as a special drought, the worst category.

This month, 59.64% of the state was classified as being in extreme drought, the second worst, with just 0.18% in an exceptional drought condition – but then it was May. right July.

Drought has a cumulative effect. As droughts intensify, exacerbated by climate change, Governor Gavin Newsom recently warned that mandatory statewide water restrictions may once again be necessary, like when Jerry was Brown is also governor.

Evidence of a warming planet is evident in the global temperature measurements. The National Oceanic and Atmospheric Administration this month said April 2022 tied with April 2010 was the fifth warmest April on record in 143 years. The 10 warmest Aprils have occurred since 2010, and the months of April for the years 2014-2022 all rank among the 10 warmest months on record.

Fire Potential Wilderness in the American West

Northern California is forecast to have an above-normal wildfire potential in June.

(Paul Duginski / Los Angeles Times)

Higher-than-normal temperatures increase the need for evaporation, which is essentially a measure of how thirsty the atmosphere is. It is a way to quantify moisture loss due to factors such as temperature, wind speed, humidity and solar radiation. Periods of above-normal temperatures and increased evaporation dry out soil and vegetation, making plants more stressed and more flammable, which facilitates the rapid spread of wildfires.

The National Federal Fire Center forecasts an above-normal June probability for major wildfires in Northern California, primarily north of the Interstate 80 corridor, with the rest of the state normal fire is expected.

Temperature outlook map for June, July and August.

Above-normal temperatures are preferred for most of the West.

(Paul Duginski / Los Angeles Times)

The outlook for June, July and August released by the National Weather Service’s Climate Prediction Center this month shows above-normal average temperatures for most of the United States, with a probability of highest in much of the west. Coastal California has a 33% to 40% probability of above-normal temperatures. Inland deserts, valleys and mountains have a 40% to 50% chance of above-normal temperatures.

The highest likelihood for above-normal temperatures is in the Central Great Basin and the central and southern Rockies, parts of an area drained by the Colorado River. The Los Angeles area typically depends on the Colorado River for about a quarter of its water, according to Southern California’s Metropolitan Water District.

Rainfall outlook for June, July and August.

Above-normal rainfall is expected in southern Arizona due to intensification of monsoons.

(Paul Duginski / Los Angeles Times)

The June-August rainfall outlook shows below-normal rainfall from the Pacific Northwest into the Plains, including the Rockies and the upper Colorado River. Much of California falls into an area with equally above, near normal, or below normal rainfall. But normal rainfall during the summer months in California is essentially absent, due to the Mediterranean climate.

One bright spot in the outlook for the Desert Southwest includes above-normal prospects for an intensifying monsoon. In northern Arizona, 40% to 50% of the annual precipitation occurs during the monsoon. Southern Arizona receives about 32% of its normal annual rainfall during the monsoon.

“The monsoon season could bring higher humidity to Southern California, which could lead to more uncomfortable nights towards the end of the heat wave,” said Eric Boldt, a meteorologist with the National Weather Service in Oxnard. serious”. The regular season begins shortly after July 4 in LA County and continues through September, he said.

Monsoons can bring thunderstorms to the mountains around LA, and that could mean lightning strikes. But there has been very little monsoon thunderstorm activity in the mountains over the past two or three summers, he said. Last season, major thunderstorm activity remained in Arizona and eastward. “You could say we’re overdue, but that doesn’t affect the outlook because we’re still in the same La Niña pattern as we were a year ago,” he said.

Alex Tardy, a meteorologist with the weather agency in San Diego, said the backing La Niñas could be responsible for the active southwest monsoon forecast, but we are already in a La Niña year. 2020 and it’s been a less monsoon year, said Alex Tardy, a meteorologist with the weather agency in San Diego. That year, a stronger-than-normal upper ridge was directly overhead, creating excessive heat. While we don’t have a monsoon in 2020, the monsoon is active in July, August and September 2021. There were 10 separate coastal thunderstorms from LA to San Diego, even as early as October, making 2021 The most active for such events since the summer of 2015, Tardy said.

Equatorial sea surface temperatures and atmospheric conditions in the tropical Pacific are consistent with La Niña, according to NOAA. Over the past four weeks, below-average sea surface temperatures have strengthened in the Niño 3.4 region, which lies midway across the equator in the eastern Pacific Ocean. Enhanced convection was observed over the Philippines, which is also consistent with La Niña. Convection is the process by which air heats and moisture rises, creating clouds and thunderstorms. Stronger east-to-west trade winds push warm water into the western Pacific, where it causes more evaporation, more clouds, and more rain, as well as more tropical cyclones or hurricanes.

La Niñas is associated with dry winters in the southwestern United States. They are also associated with busy hurricane seasons in the Atlantic basin. This week, NOAA predicts that 2022 will be the seventh consecutive above-average Atlantic hurricane season. NOAA says there’s a 65% chance the season, which runs from June 1 to November 30, will be higher than usual. The outlook shows 14 to 21 named storms, of which 6 to 10 could become hurricanes. That number could include three to six major hurricanes, that is, category 3, 4 or 5.

Meanwhile, in the central Pacific, there is a 60 percent chance of tropical cyclone activity below normal, NOAA said. “The ongoing La Niña has the potential to cause strong vertical wind shear, making it difficult for hurricanes to develop or move into the central Pacific,” said forecaster Matthew Rosencrans.

La Niña is expected to continue, with the odds falling in late summer before increasing through fall and early winter.

With all of the factors, including climate change, increasingly severe droughts, dwindling reservoirs and mandatory state-wide water restrictions possible, the summer heat and risk fire, one interpretation of Margo Channing’s advice in “All About Eve” might be appropriate: “Fasten your seat belt; It’s going to be a bumpy summer. “

https://www.latimes.com/california/story/2022-05-26/heat-and-drought-shape-southern-californias-summer-outlook Heat and drought shape Southern California’s summer outlook

Edmund DeMarche

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