Knowing your time zone (Pacific) is a good start. But of course you also will probably want to account for whether daylight saving time is in effect, making the difference -7 hours rather than -8. If your server is set to the Pacific time you want (standard or daylight), you may use the DateDiff between getDate() and getUTCDate() as your offset, using DateAdd to apply it to your UTC time.
Declare @MyDateUTC datetime
Set @MyDateUTC = '2009-04-19 04:12'
select @MydateUTC as MyDateUTC
,DateAdd(hh,DATEDIFF(hh, GetUtcDate(), GetDate()), @MyDateUTC) as MyDatePacific
2009-04-19 04:12:00.000 2009-04-18 21:12:00.000
(1 row(s) affected)
Of course, the current difference (-7) may not be valid if you're looking at a date from February, for instance. For an application that looks at historic times and needs to convert any from UTC to Pacific Time, I'd think you'll need a table of the start and end dates for Daylight Saving Time to know whether it's -7 hours or -8 hours. A web search should turn up the basic data for you. Depending on how far back you go, the dates and rules for determining the dates Daylight Saving Time started and ended have changed many times over the years.