UPDATE 11:54 a.m.

A new revenue forecast released this morning taxed reporters’ brains. Some would say that’s not hard to do.

But the reason heads were hurting was because of a weird discrepancy: State Economist Arun Raha‘s forecast for tax collections shrank by only a small amount from his March estimate ($12 million — or $183 million if you start counting next month after most of the effects wear off from a big windfall, the state’s tax amnesty program). But lawmakers and the governor’s office said it reduced their budget cushion by a whopping $575 million.

Just a day ago, when Gov. Chris Gregoire signed the two-year budget, it contained a cushion of $738 million in case of emergency. That balance has now dropped to just $163 million.

As we tried to get our heads around the difference, budget director Marty Brown explained the biggest part of it came from lawmakers moving money around, so it looked like extra tax collections in Raha’s data but actually wasn’t more than what was budgeted. Plus, lawmakers thought the current year’s revenues would jump more than they did based on the amnesty program.

Brown scribbled some notes on the balance sheet (picture below) to help us understand.

Despite the change that almost wipes out the ending fund balance, Brown said he doesn’t think Gregoire needs to call lawmakers back into a special session, barring a “gigantic” change in future forecasts this fall.

That’s because lawmakers aren’t facing the clock like they were last year when they held a special session. They have a while to make the cuts.

“Right now, I don’t think it’s a major problem, because we’ve got two years,” Brown said.

Raha’s gloomier revenue forecast accounts for slower economic growth since March.

He blames it on national and international factors, including turbulence in the Arab world and earthquakes in Japan.

He says the growth should pick up in the second half of 2011.