Here are the updated results, just in. Prosser needs 225 more votes to win by 1 vote. The one precinct left is in Jefferson County, and my calculation predicts Prosser will pick up 89 votes there. Not enough.
(My calculation assumes the last precinct has the same number of voters as the average in the other Jefferson County precincts and that the relative popularity of Prosser and Kloppenburg is the same as the rest of the county. This prediction method worked well in predicting what would happen with a couple other late-reporting counties.)
UPDATE: All reports in.