Western U.S. states are bracing for a brutal early-season heat wave that threatens to hit several cities over the weekend and into next week. Forecasters warned that temperatures will rise 20 to 30 degrees above normal for several days.
Daily records could be broken in Southern California this week, the National Weather Service said, with the possibility that March’s all-time records could also be broken. Following the warmest winter on record for most of the region, the intense conditions are expected to impact low snowpack levels, deepening drought concerns.
Caused by a large, persistent pressure dome sitting over a large swath of the West, the heat blasts are expected to arrive in two waves, first hitting the West Coast on Thursday and spreading eastward across California, Nevada, Arizona and New Mexico. Another stronger round will begin Monday and reach Utah, Colorado, Oregon, Idaho and Wyoming.
By Tuesday of next week, areas where approximately 26.4 million people live will be affected by moderate heat risks, the second of four levels designated by the NWS, which will most affect sensitive populations and those without access to cooling or hydration. Tens of thousands of people could face extreme heat (the highest level) without relief overnight.
Extreme heat early in the year could pose greater dangers to public health. “This time of year, the body is not used to dealing with this level of heat, so these highs are more impactful now than they were in July,” NWS meteorologists in the San Francisco Bay area warned in a post Thursday on social media.
“The next 10 to 14 days look truly exceptional across the Western United States, and not in a good way,” climate scientist Daniel Swain wrote about the event on Wednesday. He said a high-pressure ridge among the strongest “ever observed in the southwestern United States in March” was expected to develop by Friday, but its records would not hold for long as it “reorganizes into an even broader and stronger ridge next week.”
With a high probability of historic heat in early spring, some records could be broken for seven to 10 consecutive days, Swain said. Temperatures could exceed 100°F (37.8°C) in Los Angeles, up to 90°F (32.2°C) in the San Francisco Bay area and possibly as high as 110°F (43.3°C) in the southeastern deserts, pushing the region into summer conditions months earlier than usual.
The heat wave comes as water managers across the West nervously watch declining snowpacks, which are expected to shrink even further. There were hopes that another cold storm would bolster the depleted snow, which was relied upon for water supplies during the warmer months. The heat also removes more moisture from landscapes, amplifying wildfire risks and extending the seasons when ignitions can quickly turn into infernos.
“During the next period of exceptionally long heat, which will bring T-shirt and shorts weather to even the highest mountains of the American West, melting will accelerate dramatically,” Swain said.
The spring snowpack, measured on April 1, “may well be the worst on record for many, if not most, watersheds in the western United States.”
