Furuno MFD12 Operator's Manual page 198

Lightning
The lightning icons show where lightning has hit, within the last 5, 10 and 15 minutes.
The fill color of the icon indicates when the lightning hit occurred. See the table below
for color and period. The number of lightning bolt markers indicates the number of
times lightning has hit.
Lightning
icon
Orange
Medium yellow
Light yellow
To find simple lightning information, put the cursor on a lightning icon. For additional
information, push the left-click button.
Description of lightning icons
Color
Simple lightning information
Detailed lightning information
11. Sirius Weather Receiver
Lightning
icons
Period
Last 0-5 min.
Last 5-10 min.
Last 10-15 min.
11-9