The agreement hinges on assumptions that could change with the eventual adoption of the state budget, which represents the overwhelming majority of district revenue, Sheehan said.
The agreement, reached late Tuesday, must also still be ratified by the Board of Education and the union's members.
Public education funding has been cut $17 billion in the last two years, and stands to lose another $2.4 billion, according to a May revision to the governor's proposals.
The agreement requires teachers take two furlough days this year, three next year and four in 2012-13. The two furlough days scheduled this year would be withdrawn if the school district receives up to $5 million through federal stimulus money Congress approved earlier this month. Those funds were also used to rehire more than 40 teachers who were laid off in June.
Teachers begin voting on the contract Sept. 7, and the school board is scheduled to vote during a special meeting Sept. 10.
A rejection by the teachers union means negotiations could continue or the Board of Education could impose its most recent offer. The union could then accept the terms or strike.
The deal is the second tentative agreement this year. The first was rejected by the Glendale Teachers Assn. by a vote of 587 to 414 in April. Union President Tami Carlson said the 18-month process was worth Tuesday's outcome.
"I don't think we would have gotten his deal without doing all this," she said.
A central difference between the two agreements is the number of teachers who would be affected by a maximum medical benefit contribution by the district. Teachers had resisted a cap, but both sides compromised and a medical benefits cap will rise by 8% every year.
"The 8% annual increase on the cap is big, it's huge," Carlson said. "Most people with caps don't have an annual increase. They have to negotiate it."
District officials typically budget an annual 10% medical benefits cost increase, although this year's renewal was higher than expected.
Throughout Wednesday, district and union officials said they were relieved they had struck a deal after 11 hours of negotiations the day before.
"Over the last month, the tone and the cooperation between the Glendale Teachers Assn. and Glendale Unified School District has improved dramatically, and I attribute that to our new superintendent and new [staff]," Carlson said. "I hope to continue to build on that. It's a whole different atmosphere."