SAN JOSE -- Mayday! Mayday! April's proverbial showers are expected to turn into a sweat storm Wednesday, leaving the Bay Area a sodden mess of wilted May flowers and maypoles drooping in the heat.
The National Weather Service forecast near-record highs in the 90s Wednesday and Thursday in some Bay Area cities -- the result of a freakish dome of high pressure and hot air that meteorologists call an "Omega Block" -- turning the last day of April and the first day of May into the alpha-dog days of summer.
Demonstrating a hitherto undiscovered flair for classical symbology, the Weather Service declares an Omega Block when a mass of high pressure -- this one rising about 20,000 feet above the California coast -- arranges itself in the shape of the last letter in the Greek alphabet. At the top of the dome, it can get as chilly as 12 degrees, while hot air is forced down to ground level. This block began forming Monday, when forecasters issued a hazardous weather outlook, warning of a 20-degree spike in the heat on Wednesday and Thursday, followed by an equally quick plummet back to the low 70s Saturday -- a six-day swing of 40 degrees.
"The high pressure overhead acts kind of like a roadblock," said Matt Mehle, a meteorologist at the National Weather Service in Monterey, "so the cold air is staying north of the West Coast." He likened an Omega Block to the furrow of high pressure that so obstinately fended off rainstorms over California this winter that it became known as the Ridiculously Resilient Ridge. The current weather pattern won't be particularly resilient, but the Omega Block will bring mega-heat.
In addition to the high pressure and warm air hovering overhead, another factor will contribute to the first major warm-up of the year: Winds that customarily blow in from the ocean have reversed themselves temporarily, bringing parbroiled breezes from the east. That increased the danger of fire, especially in local hills, although wind gusts weren't expected to pose the same threat here as in Southern California, where gusts of 55 mph were forecast through Thursday.
In San Jose's Brokaw Commons shopping center, where the temperature reached 86 degrees Tuesday, Amanda Rodriguez was already rolling up her sleeves as she left work.
"I have tattoos, so I usually have to wear long sleeves, and in the summertime it's just horrendous," she said. "So I do enjoy the heat, but not this early in the year. I still want that nice 70s weather, to enjoy the springtime before we get this huge heat wave."
Maybe not the be-all and end-all of heat waves but certainly the alpha and the Omega of hot.
Contact Bruce Newman at 408-920-5004. Follow him at Twitter.com/BruceNewmanTwit.
San Jose 91 89
Gilroy 96 94
Livermore 93 93
Walnut Creek 92 91
Mountain View 90 88
Oakland 86 83