In the November 2008 issue of By the Numbers, Jim Albert looks at hitting streaks and provides results that streaks happen more regularly than they should. The research was solid, except where he assumes the ability to get a hit is equal across a season. The ability to get a hit though is not constant across a season. This difference can be seen in the article, Changes in League Averages Over the Course of the Season by Brian Morrow, which was also published in By the Numbers. Brian shows that there is a 3% change in the number of hits per PA across the season, with the peak in the middle of the season and low points at the beginning and end of the season. This change is probably do to the increase in hits do to the extra distance a ball travels as the temperature increases. Balls hit when it is hotter face less air resistance therefore act like they were hit harder than they actually were and will travel further.
I decided to look to see when hitting streaks occur and if the time of the season is important. I took the 100 top hitting streaks from the past 10 years (20 game streak is the minimum) and marked how many of these streaks where happening each day. If a streak went from one season to the next, both ends of the streak were included. I also included the average temperature of the all the games for the last 10 years. Here is the results:
Though the number of streaks doesn't perfectly increase with temperature, there is a definite summer increase where twice as many streaks happened as compared to the spring and fall. A streak can't be 100% attributed to the weather, but it can't be dismissed that streaks happen more often in the warm summer months.
Jim's article is not the only case where a writer assumed that stats are put up evenly across a season, which they are not. Many people assume that pitching dominates the post season, but when you are playing when it's 40 degrees F out side, the ball will not travel as far as when it is 100 degrees F (~42 feet less on a 400ft HR).
When you start hearing that a hitter is heating up and on a streak, it may not be all him, mother nature may also be playing a role.