▁independent , ▁with ▁no ▁way ▁to ▁reference ▁the ▁G RI B ▁writer ' s ▁intended ▁schema ▁▁ ▁No ▁fool proof ▁way ▁to ▁combine ▁records ▁into ▁the ▁mult id im ensional ▁arrays ▁from ▁which ▁they ▁were ▁derived . ▁ ▁The ▁use ▁of ▁external ▁tables ▁to ▁describe ▁the ▁meaning ▁of ▁the ▁data . ▁▁ ▁No ▁author itative ▁place ▁for ▁cent ers ▁to ▁publish ▁their ▁local ▁tables . ▁ ▁In cons istent ▁and ▁incorrect ▁methods ▁of ▁version ing ▁local ▁tables . ▁ ▁No ▁machine - read able ▁versions ▁of ▁the ▁W MO ▁tables ▁( now ▁available ▁for ▁G RI B - 2 , ▁but ▁not ▁G RI B - 1 ) ▁ ▁G RI B ▁ 1 ▁Header ▁ ▁There ▁are ▁ 2 ▁parts ▁of ▁the ▁G RI B   1 ▁header ▁- ▁one ▁mand atory ▁( Product ▁Definition ▁Section ▁- ▁P DS ) ▁and ▁one ▁optional ▁( Grid ▁Description ▁Section ▁- ▁G DS ). ▁The ▁P DS ▁describes ▁who ▁created ▁the ▁data ▁( the ▁research ▁/ ▁operation ▁center ), ▁the ▁involved ▁numerical ▁model ▁/ ▁process ▁( can ▁be ▁N WP ▁or ▁GC M ), ▁the ▁data ▁that ▁is ▁actually ▁stored ▁( such ▁as ▁wind , ▁temperature , ▁o zone ▁concentration ▁etc .), ▁units ▁of ▁the ▁data ▁( met ers , ▁pressure ▁etc .), ▁vertical ▁system ▁of ▁the ▁data ▁( constant ▁height , ▁constant ▁pressure , ▁constant ▁potential ▁temperature ), ▁and ▁the ▁time ▁stamp . ▁ ▁If ▁a ▁description ▁of ▁the ▁spatial ▁organization ▁of ▁the ▁data ▁is ▁needed , ▁the ▁G DS ▁must ▁be ▁included ▁as