What does N mean after a runway visual range (in a METAR)? This morning's METAR for Cambridge looked like this:

EGSC 110720Z 11001KT 0150 R23/0200N R05/0175N FZFG BKN001 M02/M02 Q1028

Note the bold runway visual range (RVR) indications. What does the N mean?
RVR often has a letter at the end to indicate the visibility trend, so you can tell if it's going to improve (and maybe you should circle overhead for a while) or worsen (and you should consider going to your alternate).

U means an "upward" trend: visibility is improving. D means a "downward" trend: visibility is worsening. N means no change.