* WHAT...Temperatures as low as 34 will result in frost formation. Temperatures may vary due to clearing or fog in localized areas. * WHERE...Portions of northwest and west central Washington. * WHEN...Until 9 AM PDT this morning. * IMPACTS...Frost could harm sensitive outdoor vegetation. Sensitive outdoor plants may be killed if left uncovered. * ADDITIONAL DETAILS...The growing season officially ends on October 31, after which no further frost or freeze headlines will be issued.