When working a local position, you should post and update at ATIS for the airport. This is accomplished with the vATIS program.
Go to the Downloads page of the ZSE website and find your applicable facility file. These are grouped by the radar facility when applicable.
When you open vATIS, you will be able to import the facility file, and then open it. Once you import it, it will be automatically updated with any changes made by the Facilities department.
Pick a status from the dropdown at the bottom of the window that matches current conditions.
Click Connect to put your ATIS online. For airports other than SEA and PDX, you should also click Record ATIS and then record yourself speaking the full ATIS.
See the documentation for more info on using vATIS
The ATIS is based directly off of the current METAR. Using the following as an example:
METAR KHIO 192253Z 12012KT 10SM SCT019 BKN055 09/04 A2966 RMK AO2 SLP044 T00890044
Your would say the following when you record the ATIS:
"Portland-Hillsboro information Alpha, 2 2 5 3 Zulu. Wind 1 0 0 at 1 2. Visibility 1 0. Ceiling 5 thousand, 5 hundred broken. Temperature 9, dewpoint 4, altimeter 2 9 6 6. Landing and departing runway 13R. Expect the ILS approach. Advise on initial contact you have information Alpha."