This afternoon’s temperatures in Santa Clara are expected to push the 100-degree mark, nearly 20 degrees above normal, prompting California's power grid operator to issue a flex alert to encourage state residents to conserve energy this evening to avoid blackouts.

The high temperatures are to continue through the weekend.

The Bay Area also will be under a Spare the Air Alert, after the Bay Area Air Quality Management District said Wednesday that high temperatures are expected to combine with vehicle exhaust to create an excessive amount of smog.

The California Independent System Operator encouraged residents across the state to reduce their energy use between 5 and 10pm tonight by setting thermostats to 78 degrees or higher, cooling rooms with fans or by closing curtains, turning off unneeded lights and avoiding using large appliances.

Officials said Wednesday that they are not currently forecasting rolling blackouts similar to the ones the state saw during heat waves last August and September.

“The current forecast for shortage is relatively modest,” said system operator CEO Elliot Mainzer during a briefing on the flex alert, adding that the alert was issued out of a “preponderance of caution.

The National Weather Service predicted a high temperature in San Jose this afternoon of 99 degrees. The city’s high temperature only hit the century mark in June on one occasion, on June 10, 2010, according to weather service data.

Nighttime temperatures in San Jose should drop to 63 degrees, according to forecasters, but then soar again on Friday, with a high of 96 degrees.

The high temperatures this weekend in San Jose are expected to be in the low 90s, still more than 10 degrees above the typical high temperatures in June.