From Met Office
RVR tendency (U = increasing; D = decreasing; N = no change; not
reported in UK at present) may be added after figure e.g.
R27R/1100D. P1500 = more than 1500 m; M0050 = less than 50 m.
Significant variations — example : R24/0950V1100, i.e. varying
between two values.