THE BUDGET PICTURE keeps getting rosier in the Rose City.

The City of Portland Budget Office revealed December 15 that the city should have at least $11 million more than expected to play around with in its general fund next year, a year after its coffers swelled with $49 million in unexpected cash.

Turns out tax revenues, from property taxes and businesses and hotels, are shooting up even faster than expected in these boom times.

"This year will likely end up being the fastest year of local economic growth since the tech bubble in the late 1990s," the city economist, Josh Harwood, wrote in the forecast.

It's good news—particularly three years after the city was forced to cut more than $20 million to plug a gaping deficit. But here's the catch: that $11 million? It's one-time-only money. And it's already sort of spoken for.

"Revenues are increasing fast," says Budget Director Andrew Scott, "but our obligations and needs are rising faster."

Here's how $11 million can melt away:

• First, slash the forecast money in half, since Portland City Council has a policy of spending half of one-time surplus money on the city's growing list of maintenance projects. The city could always elect to override that rule, Harwood notes, but it might not be likely at a time when the city's roads are hurting.

• From the remaining $5.5 million, chop $1.4 million to fund 13 firefighter positions that are currently being paid with grant money that's set to expire. Now you've got $4.1 million.

• But you've also got dozens upon dozens of parks workers you've been underpaying for years, who've now won the right to union protections. That's a minimum $2.3 million extra a year—and could well be twice that much, depending on what happens in ongoing negotiations.

• There's more: police body cameras, new police background investigators the city just voted to hire, an upcoming proposal to snatch $1.2 million from Airbnb taxes to build affordable housing.

And these are just the existing commitments the city will either have to fund or axe. There will also be millions of new requests from city bureaus.

All of which gets to Mayor Charlie Hales' approach to next year's budget. Last month, Hales issued a directive to every city department except the Portland Housing Bureau to figure out how to hack 5 percent of their expenses next year.

"Portland is in the grips of an affordable housing and homelessness crisis that requires additional resources to invest in the most effective approaches," Hales wrote. "We are experiencing an increase in gun-related violence that requires a robust response."

Hales said he'd "address these issues head on" and that that might take trims—even in a prosperous year.

It might not be as tough as all that. Harwood concedes the city forecasts conservatively, and that there will likely be more money to play with when the carving knives come out for next spring's budget work.

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Will it be enough to satisfy Portland's ever-raging fiscal thirst?

Is it ever?