Does the Association have a standard letter to communicate to staff what COVID-19 is and why we might need to close?

No, at this time members should work with HR and/or attorney to draft clear, regular communication to employees. Start here with this official note: https://www.governor.wa.gov/news-media/inslee-statement-statewide-shutdown-restaurants-bars-and-limits-size-gatherings-expanded. Then tailor something for your staff.

The Department of Health has excellent resources on what it is. https://hub.wahospitality.org/coronavirus-resource/coronavirus-fact-sheets/