http://www.collegedata.com/cs/data/college/college_pg02_tmpl.jhtml?schoolId=764 says that only 11% had high school GPA under 3.50.
Also, many majors at Washington are impacted; see http://www.washington.edu/uaa/advising/academic-planning/majors-and-minors/list-of-undergraduate-majors/ . With below average high school GPA, if your intended major is one of the ones with more competitive admission, it is unlikely that you will get direct admission as a frosh, and it may be an uphill climb to get the needed college GPA to be competitive to get into the major later. Of course, if your high school GPA is low due to conditions that no longer apply (e.g. poor 9th-10th grade, but you turned it around and have straight A grades in 11th-12th grade), then that may be a positive sign (though there is still uncertainty about getting into competitive majors).