Fresno-area heat wave: When can we expect things to cool off?
An excessive heat warning from the National Weather Service remains in effect in Fresno, Merced and other Valley counties through at least Thursday, with high temperatures expected to remain above 100 degrees through Sunday.
“We’re in the hottest period of this excessive heat that we’ve been experiencing,” said Jim Bagnall, a meteorologist with the weather service office in Hanford.
Sunday’s afternoon high of 112 in Fresno topped a 100-year-old record for the date. The previous record of 110 degrees was set in 1920. And in Merced, an afternoon maximum temperature of 111 degrees on Sunday smashed the previous record of 104, set in 2015.
The rest of this week were expected to bring slightly lower temperatures, but not low enough to count as a cooldown, Bagnall said. “Let’s say it’s going to be less hot,” he said. “The highs will go down a few degrees. But the overnight lows are what’s been driving some of the heat risk factors. We don’t get a chance to recover from the afternoon heat when the lows are not going below 80 degrees.”
Monday reached an afternoon high of 108 in Fresno and 107 in Merced. Through the rest of this week, temperatures were expected to reach 108 Tuesday, 106 Wednesday and 103 Thursday and Friday, before ticking up again to 104 Saturday and 105 Sunday.
Madera set a record Monday with a high 109, breaking the previous mark of 108.
Merced’s high temperatures were forecast for 107 Tuesday, 105 Wednesday, 102 Thursday and Friday, 103 Saturday and 104 Sunday.
The average high temperatures for this time of year are in the high 90s in Fresno and the mid-90s in Merced.
Fresno had a 10-day run of afternoon highs at or above 100 degrees earlier this summer, from July 26 through Aug. 4.
Heat wave explained
The current heat wave that began Friday is forecast to bring at least 10 straight days of temperatures over 100 degrees to the region. The culprit, Bagnall said, is a ridge of high pressure that has settled into the four-corners area of the southwestern U.S., where Utah, Colorado, Arizona and New Mexico intersect.
“There’s a big strong area of high pressure centered right now in the four corners to the southeast of us,” Bagnall said. “As that thing expands and builds westward over us, it causes our temperatures to go up.”
The meager dip in temperatures to the low 100s will be the result of the expected movement of that high pressure area to the south.
Dangerously hot conditions will occur during the afternoon and early evening hours each day,” the heat warning issued by the National Weather Service noted. “Extreme heat and humidity will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities.”
The heat warning also advises people to “drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors.”
“Take extra precautions if you work or spend time outside. When possible, reschedule strenuous activity to early morning or evening,” the warning continues.
Why Merced is cooler
Merced typically enjoys temperatures that are slightly lower than those in Fresno and the southern San Joaquin Valley. “Merced is closer to the influences of the Bay Area and the Delta, and the marine influence (from the Pacific Ocean) reaches them more frequently,” Bagnall said. “And Fresno is a larger urban area that typically is going to record higher temperatures” with more buildings and concrete surfaces to absorb heat and radiate it back into the air.
The high-pressure area that’s blocking any marine cooling for the Valley also causing more widespread problems.
“The hot and dry conditions will lead to elevated/critical fire danger, especially from the Great Basin to portions of the northern Intermountain West,” stated a weather service forecast issued Monday afternoon.
This story was originally published August 17, 2020 at 2:26 PM.
