Thinking of buying Apple stock before the WWDC announcements tonight? The advice seems to be hold tight, even revamping its entire range of Macs, showing off OS X Mountain Lion and iOS 6, and unveiling an SDK that makes developing for the Apple TV might not be enough to send the share price into space.

Forbes has taken a look at the effect of WWDC announcements on Apple’s share price. According to the report: “The data shows that the Monday of WWDC is a horrible day to buy Apple stock.”

The report notes that since 2003 Apple stock has always closed below where it closed on the Friday preceding WWDC on the day of the keynote.

“It seems that investors never think that the presentation meets expectations,” writes Forbes.

It should be noted that over the years Apple’s biggest announcements have happened at Macworld San Francisco, or shortly after that show, so it may well be that in the absence of any other announcements this year, Apple’s WWDC show may become the new venue for big, share price affecting announcements.