Such a declaration would enable greater federal aid and reimbursement to the state for its response to the disaster. The Everett Herald reports that Inslee is requesting support for the following programs:

Disaster housing, which provides up to 18 months of temporary housing aid for those whose residences were heavily damaged or destroyed. Funding also can be provided for housing repairs and replacement of damaged items to make homes habitable.

Disaster grants, which help individuals pay for disaster-related needs and necessary expenses not covered by insurance and other aid programs. These may include replacement of personal property, and transportation, medical, dental and funeral expenses.

Unemployment insurance benefits for those who became unemployed as a result of the disaster.

Crisis counseling program, which provides funds for services to disaster survivors, responders, and others impacted by the disaster.

You can read the whole letter, which is a comprehensive and data-rich overview of the disaster and the response to it so far, here (PDF).