SMA PLT DEPARTS SVFR AFTER SUNSET.

Narrative

OSH HAD SNOW SHOWERS OFF AND ON DURING THE AFTERNOON. I CHKED THE WX EVERY HR OR 2. I RECEIVED MY PRE-DEP BRIEFING BY WXMATION; DEST WAS VFR. REMOVED ALL SNOW FROM THE ACFT AND MONITORED ATIS. WX WAS M 27 OVERCAST 1 SW. UPON TAXI OUT AND SVFR CLRNC REQUEST IT WAS 7 OVERCAST 1 1/2 SW (I THINK INFO XXX). SVFR CLRNC WAS RECEIVED. TKOF WAS TO THE EAST AND TURNOUT TO THE NE. THE SVFR CONDITIONS WERE LOCALIZED AND CONDITIONS IMPROVED AFTER TKOF. THE FLT TO MTW WAS VFR AND AWOS AT MTW WAS NO CLOUDS BELOW 12000 AND 3 1/2 MI UPON ARR. VERY LIGHT SNOW WAS THE RESTRICTION TO VISIBILITY. MY CONCERN: I MAY HAVE DEPARTED AFTER SUNSET AT OSH; SVFR. MY QUESTION: IF THIS WAS THE CASE; WHY ISN'T IT THE POLICY OF THE TWR (IF HE WAS AWARE OF IT) TO ADVISE ME THE SAME. SOMETIMES THE OBVIOUS IS OVERLOOKED AND A LITTLE HINT FROM AN OUTSIDE SOURCE TURNS THE LIGHT ON! LACK OF COM CAN BE A KILLER; AS WE LEARN IN COCKPIT RESOURCE MGMNT. THE FINAL DECISION IS WITH THE PIC BUT OUTSIDE HELP; BOTH IN THE COCKPIT (EVEN FROM THE PAX IN MY PRIVATE AIRPLANE) OR ATC IS WELCOMED BY ME AND I THINK SHOULD BE POLICY BY ATC WHEN OBVIOUS.