A record heat dome is about to hit the West — in March

A record-breaking heat dome will develop near the West Coast late this week, smashing records and sending temperatures into the triple digits through next week – when it will feel like summer during the final days of winter.

This follows the warmest start to March on record for the United States.

There are many potential firsts for March on the horizon: It could reach 100 degrees in Los Angeles this week, after record-breaking 95-degree heat on Thursday and Friday. In Phoenix next week, temperatures could exceed 100 degrees several times. It could also reach the century mark in Las Vegas.

The pattern is occurring as a marine heat wave builds offshore, an expansive area of well-above-average sea temperatures that is likely to expand as summerlike warmth arrives and intensifies into next week – following a meteorological winter with widespread record-breaking warmth and snow droughts in the West.

“I’d say the pattern next week would be the nail in the coffin of a very unforgettable winter season,” said assistant Utah state climatologist Jon Meyer, who was “quite pessimistic” about the potential impacts on the state’s water supply and drought conditions.

How hot it will get

Extreme heat will come in two main waves for the West, with around 20 to 25 million people forecast to be in moderate (Level 2 out of 4) heat risk at times into next week according to the National Oceanic and Atmospheric Administration.

At that level, excessive heat can affect those who are sensitive to it, those without cooling and/or hydration and some health systems and industries.

The first wave arrived Thursday, bringing record-breaking warmth to the Southwest, including California, Nevada, Arizona and New Mexicothrough the weekend.

A second, stronger heat wave will arrive Monday, with record-breaking heat spreading farther and wider – reaching Utah, Colorado, Wyoming, Idaho and Oregon.

Widespread high temperatures in the 80s, 90s and lower 100s are forecast across the Southwest through the weekend – as much as 30 degrees above average in some areas – before the bubble of heat expands and intensifies next Tuesday.

Monthly records could fall in Salt Lake City, Denver and Reno, Nevada, next week, where it will probably reach the 80s.

Climate scientist Daniel Swain described the pattern as a prolonged and very likely record-breaking heat wave that would not reach its peak for another week to 10 days. It is expected to induce rapid melt of remaining snowpack.

“This forecast is truly extraordinary for March,” he said.

The heat dome will also have a less obvious consequence: It could indirectly contribute to flooding rain in Hawaii. This strong and tall mountain of high pressure in the West will create a blockage in the atmosphere, allowing a train of storms to hit Hawaii relentlessly through this weekend.

Worsening drought

This record-breaking heat dome will contribute to worsening drought conditions across the Intermountain West.

In Utah, snowpack remains at record low levels according to Meyer. He said that it would take a foot of snow in Salt Lake City for the season to catch up with even the second-lowest seasonal snowfall total – and that a storm of that magnitude isn’t expected to come.

“The knockout punch comes in the form of Utah’s reservoirs, which are only at 40 % of capacity right now,” Meyer said. “All this means we are likely going to see some very tangible water supply cuts and conservation efforts by the state this year.”

The weather forecast and climate outlook community in Utah was “filled with trepidation” because drought relief looked unlikely, added Meyer, stressing that much more meaningful impacts were possible for agricultural communities as water conservation efforts grow.

“Right now, every drop is going to count this year,” he said.

Across the region, New Mexico was also reporting its lowest snowpack on record and Colorado was in a similar situation. Because of several strong storms during fall and winter, California is the only state that is currently drought free.

Marine heat wave

Sea surface temperatures off the coast of Southern California have risen as much as 5 degrees above average for the time of year, causing a strong, Category 2 marine heat wave to develop.

These unusually warm waters will provide a boost to air temperatures near the coast, especially at night, preventing them from dropping off as much as they otherwise would.

The heat dome will bring light winds, plentiful sunshine and unseasonably high temperatures, which will prevent cooler, deeper waters from churning up. The sea surface will warm, further intensifying the marine heat wave.

This can contribute to a feedback loop, by which extra warmth in the sea adds to warmth on land and vice versa.

As the climate warms, marine heat waves are becoming more frequent, severe and long-lasting.

“A strong to severe marine heatwave is ongoing off the coast of California,” wrote Colin McCarthy, a storm chaser affiliated with the University of California at Davis.

In early March, ocean temperatures reached the mid- to upper 60s at Scripps Pier in La Jolla, California.

“That’s the average ocean temperature for mid-June,” McCarthy said.