Washington has a cost of living index of 115 relative to the US average of 100. This is above the national average. A FIRE portfolio in Washington needs to stretch further. Many FIRE practitioners in WA plan for a higher withdrawal need or consider relocating to lower-cost states.
The 4% safe withdrawal rule suggests a FIRE number of 25x annual expenses. At Washington's median income of $82,400, that is $2,060,000. However, if you plan to spend more (or less) than median income in retirement, scale the number accordingly.
Washington has no state income tax. Roth conversions, capital gains distributions, and IRA withdrawals all avoid state tax in WA. This makes Washington one of the most FIRE-friendly states from a tax perspective.