The back portion of section 128 is protected by the overhanging seating above, and your best options for the most protection will be the last 3 rows (Rows FF-HH). Row DD will have some protection from the sun, but on rainy days you might get wet depending on how the wind is blowing.

Cover down third base line at PNC Park
The last few rows of sections down the third base line at PNC Park are covered by an overhang, as shown by the picture above.