The colors relates to the number of lightning strikes in the last 30 mins.
Also an overlay plot of last main synoptic (:00) hour METAR observed
thunderstorms and cumulonimbus.
Decoding time stamp example:
Sferics plot/041224/2000
041224/2000: year=2004; month=12 (December); day=24; 2000=20:00 UTC
