The weather today will most likely be the same as the weather tomorrow
Yesterday’s weather is an Extreme Programming (XP) term to keep teams from over committing during sprints and iterations.
Yesterday’s Weather is a Scrum pattern that helps Teams quickly calculate how many Points they will likely complete in the upcoming Sprint. The name comes from the fact that the best predictor of today’s weather is yesterday’s weather. In most cases, the number of Points completed in the last Sprint is the most reliable predictor of how many Points will be completed in the next Sprint.
The story goes something like this. Once upon a time there was a government spent a boatload of money on a weather prediction satellite. It took years. Cost of millions of dollars. But they were finally able to launch a satellite that was able to accurately predict the weather about 70% of the time. Not bad.
It was then that someone realized if they simply said today’s weather will be the same as yesterday’s weather they’d also be accurate 70% of the time.
XP uses this concept to keep teams from over committing during sprints/iterations. It reminds us that a good predictor of the future is what we’ve done in the past.
Here’s how it works:
First, the Team determines their average Velocity for the past three Sprints, adjusted for team size. For example, if one person of a five-person Team is on vacation for the entire Sprint in which 50 points of work is completed, the Team’s raw Velocity (50) should be divided by 80% (4 instead of 5 Team members) for a normalized Velocity of 60 points. Normalized velocity is the number of points you would expect the team to complete if all team members are available full time.
During the next Sprint Planning, the team determines what the their percent capacity will be for the upcoming Sprint. If a fully staffed Team has five members who all work full time, but one team member will be absent for a day in the coming week-long Sprint, the team’s capacity will be 96%. (Be careful to only correct for major team member absences and not try to over-correct for minor changes in capacity.)
Finally, multiply the team’s normalized velocity by its percent capacity for the coming Sprint to determine the targeted points for the next Sprint. This technique is quick, accurate, and Jeff Sutherland says that he would not run a Scrum without including this Pattern.
Here is Scrum Inc.’s Yesterday’s Weather Tool. It does all the math for you.
