The Bay Area received an early taste of summer Thursday and San Jose even tied a 1996 record, but the numbers still don't add up to a heat wave.
"It's a warm day but nothing memorable," said Jan Null, a meteorologist with Golden Gate Weather Services in San Francisco. "You need more than a couple of days to have a heat wave."
By midafternoon, the National Weather Service in Monterey reported some record breaking high temperatures but mostly warmer-than-average highs throughout the region.
Oakland reached 90 degrees, easily breaking the 84 degrees for the same date in 1992. Downtown San Francisco hit 88 degrees, squeaking by the old mark of 86 degrees, also set in 1992. San Jose reached 92, which tied a record set in 1996.
Austin Cross, a NWS meteorologist, forecast slightly cooler temperatures starting Friday and a larger drop of about 10 degrees on Sunday.
"It just won't be as hot as it was today, just a few degrees cooler," Cross said.
Null said the unseasonably warm weather that settled over the Bay Area, from Santa Rosa in the north to Gilroy in the south, was unusual. By midafternoon, he said, the temperature was in the 80s in almost every city and large town at the same time.
"It's pretty rare for that uniformity of temperatures around the Bay Area," Null said.
Both weather services attributed the warm weather to high-pressure air that settled over the entire region and the coast on Wednesday. Usually, the atmospheric pressure over the land is low at this time of year, and it usually gives way to the high pressure fronts off the coast that normally sweep through in late afternoon with cool sea breezes.
"It's the Bay Area's natural air-conditioning," Null said, "and it's pretty reliable."
But with high pressure everywhere, the sea breezes couldn't break through Wednesday and Thursday. Worse, Null said, the warm air just sat there getting hotter under the sun, and baking the region's gasoline emissions and other air pollutants into smog. By late afternoon, it was pretty hard to see the East Hills from downtown San Jose through the muck.
The combination of heat and smog prompted the National Weather Service to issue a heat advisory for most of the day, warning people with respiratory problems to stay indoors or take it easy outside. The potential for brush fires remained high across the Bay Area.
While hot weather usually sparks negative things, from fires to high energy and water consumption, it's welcomed by the tourist, entertainment and ice-cream truck industries.
"Warm weather definitely jump starts the season," said Roger Ross, spokesman for California's Great America amusement park in Santa Clara. "When it's hot they really like the water rides. They don't mind getting wet because they know they'll dry out quick."
Despite the warm spell, however, the park won't have every ride and stage open until Memorial Day, it's traditional date for kicking off the summer season.
Meanwhile, the Sierra snowpack is 17 percent of normal for this date, according to a survey Thursday by officials of the State Department of Water Resources.
"I'm finding nothing. Seriously, there is no snow on the course at all," said Frank Gehrke, chief surveyor for the Department of Water Resources, during a visit to Echo Summit with reporters.
The historic lack of rain and snow this spring isn't leading to major water shortages in the Bay Area, however. Heavier than normal rainfall in November and December filled flooded into reservoirs around Northern California, and that early "water in the bank" means that most major water districts around the Bay Area have said there will not be mandatory water rationing this summer.
Lake Oroville, which is the main reservoir for the State Water Project, is at 86 percent of its capacity. Lake Shasta, the main reservoir for the federal water project, which primarily supplies farmers in the Central Valley, is at 83 percent of its capacity.
If next winter is dry again, however, that could lead to a drought and restrictions in the summer of 2014.
Associated Press and Staff writers Paul Rogers and Mark Gomez contributed to this report.
Contact Joe Rodriguez at 408-920-5767. Follow him on Twitter @JoeRodMercury.