Sentencing for felonies in Washington State is complex and a full understanding requires an in-depth discussion with your lawyer.
Misdemeanor sentencing is simple and straightforward and mostly a function of the defendant's past criminal history and the nature of the offense. Few first time offenders will go to jail, although some form of community service may be imposed in addition to fines. Some offenses, like DUI, have "mandatory minimum" jail times prescribed by law, requiring the judge to impose at least the minimum time.
Felonies are a very different matter. In years past, judges sentenced felons almost entirely subjectively, after which a parole board would decide if the defendant could be released early. That system led to many abuses and it was found that people of color and people of financial means, for example, were getting widely disparate sentences for the same crimes. During the 1980's a major sentencing revolution took place across the nation and most states (and the federal government) adopted a new system that abolished parole boards and established what has become known as the "determinate" sentence system. Under this system, a "sentencing grid" is used to determine what sentence an individual should receive. Along the top axis of the grid is the Offender Score and along the side axis is the Seriousness level of the offense. To determine a given sentence, a judge finds the column corresponding to the defendant's Offender score (which is based on his criminal history) and then finds the row corresponding to the Seriousness level of the offense. This exercise produces a box within the grid that contains the sentence for that offense. The sentence is usually expressed in a range of months (24-36 months, for example), giving the judge some discretion in the application of the sentence to the particular facts of the case. In some cases the judge can go below or above the presumptive range in the box (called an "exceptional sentence") but exceptional sentences are rare and most judges won't leave the comfort zone of the presumptive range.
Most felony sentences are followed by a period of "community custody" where the defendant is out on a form of "probation" while being monitored by a Community Corrections Officer (CCO).
There are statutory alternatives to jail time, including "Community Restitution" (also known as "community service hours") and Work and Education Release (WER, where a defendant is allowed to go to work or school during the day and then return to custody in the evening and weekends). There are several other specialized sentencing alternatives to confinement, too many to recount here; these should be discussed with your lawyer.