SEATTLE -- Safeco Field, the palace of the Seattle Mariners, has always been a tough place for right-handed hitters to hit a home run and the park has consistently rated among the top "pitcher's parks" in baseball.
Our infamous chilly marine climate combined with our thick sea-level air is frequently cited as major contributing factor to hitter's frustrations. Colder air is denser than warm air, so a ball won't travel as far on a chilly day as it will on a warm day. So while Safeco Field's dimensions aren't too unusual compared to other parks, it's harder to hit a home run on our cold days.
Of course, there are multiple factors in play for every game besides weather -- strength of lineup, caliber of pitching -- you would think a team facing an ace like Felix Hernandez will score less runs than if they're facing a team's No. 5 starter -- and even in-game strategies, to name a few.
But the Mariners have particularly struggled on offense this year at home -- way more than their road games. Box scores are littered with games lately where they only scored 1 or 2 runs, or were even shut out. And persistent murmurs for moving in the fences are starting to grow louder.
Yes, the offense is struggling as a whole, but I had to wonder: Has Mother Nature really thrown our hitters her own curve ball? Could this cold, damp spring and early summer have been making it even harder for Justin Smoak and Jesus Montero to hit a home run?
Let's find out.
The first challenge was to find out just how much colder than normal the weather has been this season. As we mentioned before, Seattle has one of the coolest climates in baseball already but it's been colder even by our standards.
I went back and correlated each home game to the high temperature at Sea-Tac Airport to find the difference from the normal high that day. (There is actual temperature data available for Safeco Field itself, but with no "normal" data to compare to, I wanted to keep this part apples-to-apples.)
Also, high temperatures are usually around 4-6 p.m. so the game time temperatures for night games are typically a little cooler while day games are a little warmer, but I wanted to just get a feel of how the day itself was with respect to an average day.
Next up, how to correlate that temperature data to how it affects a potential home run. Lucky for me, Alan Nathan, Professor Emeritus of Physics at the University of Illinois at Urbana-Champaign wrote an in-depth article for BaseabllProspectus.com that detailed just how temperature can affect the flight of a ball when all other factors are consistent. (The point of his article was to disprove that the rise in home runs in baseball lately was due to global warming, but the math works for what I'm looking for.)
Nathan used data from Sportvision’s HITf/x and Greg Rybarczyk's HitTracker that analyzes every home run hit in baseball these days to find the correlation between a temperature change and the flight of the baseball.
He was able to conclude that if you keep all other environmental factors constant, that for a 400-foot home run, every degree drop in temperature, a ball will travel 0.25 feet less (3 inches). 400 feet is roughly the average depth in Safeco Field's left field power alley.
Just how cold has this spring/summer been?
While April's home games turned out to be, on average, about a degree above normal, May's games were about 2 degrees below normal while June has been nearly 5 degrees colder -- pretty significant by weather standards and overall is set to place in the top 5 coldest Junes on record and top 3 wettest.
So if you figure the temperature has been 5 degrees below normal, it means that balls were traveling about 1.25 feet (15 inches) shorter than they would be under normal Seattle June weather conditions. That doesn't seem like much, and it isn't -- consider the warning track is roughly 12 feet deep. Nathan also concluded that a 1% reduction in distance corresponded to a 10% less chance of getting a home run. In this case, a temperature that robbed 4 feet off the distance of a batted ball would saddle a batter with a 10 percent less chance of hitting a home run. In our case of what our cold June has wrath, we're looking at a 0.3% reduction in distance, or a 3% less chance of a home run assuming a linear relationship.
Nathan's data would instead suggest that if you want to get that 10% home run advantage, you would need to increase the temperature by 16 degrees, which would theoretically make a 398 foot warning track out in 65 degrees instead be a 402-foot home run in 81 degrees.
What about humidity?
Believe it or not, humid air is less dense than dry air because water's molecular weight is less than air. So on humid days, the air has less friction that would allow a baseball to travel further, but on the other hand, the baseball itself gets a little heavier picking up some of those water molecules as it travels, so these effects to tend to cancel each other out and thus humidity doesn't have much of an affect on a baseball's distance.
How does wind come into play?
Using more of that HitTracker data, the site BaseballAnalysts.com looked at every ballpark and determined just how much wind came into play. Surprisingly, Safeco Field did get a very small benefit from winds that more often than not lightly blow out instead of in.
The way Safeco Field is aligned, you can see why -- on a majority of days, Seattle's wind blows from the south -- especially on cooler days. A due-south wind would be blowing out to left field -- although I'm sure the stadium itself provides some blockage from the wind. The effect is mitigated a bit in that many of our stronger south wind days would accompany our rainy days, in which case the roof would be closed and wind effects would be kept to a minimum.
But there are also frequent days when we get that marine push of air in the evening off Puget Sound -- and that is more typical of a southwest wind. If the winds blew southwest inside the park as well, a ball hit to left field would be getting pushed toward the deeper parts of the park in center field, creating a disadvantage. However, it would help left-handed hitters as it would push balls in right field toward the shorter porch -- just as long as it didn't push it foul.
On sunny and warn days, the wind would blow in from the north, perhaps mitigating a temperature advantage -- a 10 mph headwind can zap 30 feet off a 400-foot ball, according to this site, but according to that BaseballAnalysts site, significant occurrences of wind-affected trajectories are rare at Safeco Field.
Barometric Pressure's effect
Thinner air makes Denver's mile-high Coors Field a hitter's paradise -- the high altitude can add as much as 40 feet to a home run versus the same struck ball at sea-level. And considering Safeco Field is about a good Felix Hernandez water-balloon toss from Puget Sound, you can't play much closer to sea level than you do in Seattle (maybe San Francisco). But while we can't change our altitude, we can get changes in our atmospheric pressure. So then, what about cool, stormy days when the atmospheric pressure is lower? Does that thinner air help fly balls go farther and mitigate any decreased distance from cooler temperatures?
Stevetheump.com suggests a ball will travel 4 feet farther for every full inch of mercury drop in pressure -- like from 30.50" to 29.50". But pressures are pretty stable in the spring and summer around here and sure enough, June's average pressures during their home stands were quite steady, staying within 0.20"-0.30" or so.
BUT! It doesn't take much to "get back" that 1.25 feet we lost due to temperature and it is possible that the temperature effect could be mitigated by a corresponding drop in atmospheric pressure. A day of 62 with a pressure of 29.80" would be the same as 67 degrees with a 30.11" pressure.
We can't blame our colder-than-normal spring and summer for having a statistically greater effect on limiting home runs than any previous years at Safeco Field. (Drat!) Even focusing on the most extreme chunk of the baseball season's weather so far -- June -- the 1.25 feet lost due to temperature could be made up by other factors such as wind and pressure to where there are minimal differences.
But hitters would have a gripe that Seattle's weather in general makes it much more difficult to hit a home run that other parks with similar dimensions. Remember that statistic that adding 16 degrees can increase a home run's chance by 10 percent. Many other cities are playing baseball in weather that is that much warmer or more.
Thus, put Safeco Field's dimensions in, say, Texas or St. Louis and now you're not in as much of a pitcher's park (and that's not even factoring in any additional elevation benefits.) Two other extreme pitcher's parks -- San Francisco's AT&T Park and San Diego's Petco Park -- also sit at sea level and have a heavily marine-influenced climate due to their proximity to the Pacific Ocean.
So if the Mariners want to level the playing field a bit, this data would seem to suggest though that if Safeco Field's fences were just brought in 4 feet along the left and left-center, it would increase home run potential similar to warming up the air 16 degrees. In other words, a typical 70 degree day with the fences in would play similar to an 86 degree day with the current configuration.
Just can't bring yourself to move in the fences but want a better hitting advantage? Some last resorts:
- More Day Games -- Typical day in the mid 70s means the temperature during the day game can be 8-10 degrees warmer than a 7:10 pm start -- and add 2 feet to a fly ball to left center, adding 5% chance to a home run. And it'll keep the nighttime traffic away from the new NBA arena.
- Play all 81 games in July and August -- Never mind you only have 72 days to work with (double-headers!!), and good luck getting baseball to oblige, but average highs in late July and August are in the mid-upper 70s, versus the upper 50s/low 60s at the start and end of the year. Those 15-20 degrees can add 4 feet to a home run and increase odds of 10 percent.
- Move the stadium to along SR-18 at Tiger Mountain -- That extra 1,200 feet in elevation could buy hitters a good 6-8 feet on home runs and think of the construction jobs we'll create!
- Bonfires in the bullpen -- One way to heat the air a bit, especially near the home run fences. Oh wait, that hasn't worked out so well in the past...
- Trade for Albert Pujols, Prince Fielder, Mark Teixeira and Adam Dunn. Sure they all play the same positions, but those guys could hit home runs in Antarctica -- and picture of the entertainment value of seeing Prince Fielder play shortstop.
P.S. OK, so 'Juneuary' might have cost the Mariners one game
While I just went through and declared that the cold spring overall probably hasn't had much of an effect on the Mariners' offense in general, there is one particular game where an unusually chilly day might have made the difference.
On May 22, Casper Wells came up with the bases loaded in the first inning and flew out to the warning track, narrowly missing a grand slam. The weather that day was in the mid 50s(!) amid rain (closed roof, normal pressure, so no effects there). That day was over 10 degrees colder than normal, and had it been closer to normal, Wells' season RBI total would be 4 greater.
Alex Liddi probably has a beef too. His flyout to center leading off the second would have been a solo home run had it been a bit warmer.
Oh, and the Mariners eventually lost that game 3-1. So, Mother Nature says you're welcome, Texas.
Follow Up: Opponents affected by the cold air too
Dave Cameron of USS Mariner blog had been also wondering about why the offense at Safeco Field has been so down tihs year. He posted a great analysis on fangraphs.com that shows in great detail the struggles that not only our offense has had this year at home, but that opponents as well have hit much less than they do when not in Seattle.
On the other hand, he also found that our pitchers have been getting an extreme advantage here, wiht much worse statistics when pitching in other ballparks.