If there is only one lane and you did not leave it, then it seems like an easy ticket to beat, particularly if he is saying you were riding at less than 1/2 of the safe speed!
I wasn't there and I don't know what s/he saw that made them stop you. WDM is likely wet, daylight, moderate traffic. W could be windy. Everyone uses different abbreviations. I put my notes on the back of the ticket.
Which makes me think, if you want to fight the ticket, file a motion for discovery and get a copy of the back of the ticket to see what notes s/he made. That may help you figure out what you may have done that was seen as unsafe and would certainly aid in any defense.
Get a copy of FIGHT YOUR TICKET from Nolo Press.