A thunderstorm approaching Nationals Park before a game on July 18, 2012. Is weather responsible for the Nats’ poor hitting this April? (AP Photo/Alex Brandon)

The Nationals – a popular preseason pick to reach the World Series – have had their share of weak offensive outings over the first 25 games, or nearly all of April. Fans and analysts can choose one of many reasons for the slow start, as baseball is a complex sport with large elements of luck built into the game. Some have mentioned the cool weather of April as a contributor to the Nats’ struggles, but the statistics show it is probably only a minor player.

First, a little perspective on the Nats and where they stand offensively. They are actually scoring more runs compared to last year – a major league-best 98-win campaign – having tallied 93 runs in the first 25 games (3.88 runs per game), which bests the 82 runs after the early-season stretch (3.28 runs per game) in 2012.

The increased run production hasn’t led to an improved record, however; the Nats currently boast a 13-12 mark, which is three games off the pace set through early May 2012 (16-9). Their pitching is simply not as good as it was a year ago, when the team posted a 2.41 ERA (earned-run average) through the first 25 (as compared to the 3.63 ERA entering tonight’s game in Atlanta).

The 93 runs scored thus far – while an improvement – actually places the Nats in the bottom third of the league. Meanwhile, Oakland, which has been quite warm this April at around 4 degrees above normal, is the leader at scoring runs with 138 to date. Grantland’s Jonah Keri wrote an article last week that sought answers for why the Athletics’ hitting is so proficient early on. Keri bandied around the possibility that the warm Oakland weather has played a role, writing:

Dave Cameron wrote a piece for FanGraphs in June that highlighted the nearly historically cold weather Seattle had last spring. We haven’t yet developed precise metrics to figure out exactly how much weather affects offense. But a truly aberrant weather streak like we had last spring in the Emerald City should at least make us take climate into account.

So has East Bay weather contributed to the A’s offensive barrage over the past year-plus, and especially the team’s power surge? Greg Rybarczyk, proprietor of the excellent Home Run Tracker site, tracks everything from how far homers fly to how secondary factors such as weather affect home run production. What’d you find, Greg? ‘No significant difference there,’ he said.

The comments Keri cites from Rybarczyk indicate weather hasn’t affected Oakland’s home run numbers, but a broader look at the A’s run production suggests warmth might be a factor.

Related: An app that predicts homeruns based on the weather

Check out the table below. Oakland has played half (7 of 14) of its home games in warmer than normal temperatures, and in all but one of these contests, they have scored 4 or more runs.

April 2013 home game log for the Oakland Athletics. Above normal temperature departures are bolded in red, while below normal departures are bolded in blue. Three or fewer runs scored by the A’s are bolded in blue; four or more runs are bolded in red.

But a little closer inspection of the A’s performance points to another – and arguably much stronger – cause of their hit parade. Oakland has played most of their home games against bad teams, including the Seattle Mariners (10-16 win-loss record) and Houston Astros (7-18). It’s against these teams that the A’s have posted big numbers, scoring a total of 14 runs in two Seattle matchups and 22 in three games versus Houston. What’s more, Oakland teed off on pitchers with high career ERAs: Seattle’s Joe Saunders and Brandon Maurer, and Houston’s Erik Bedard, Rhiner Cruz and Bud Norris. The 3.91 ERA punched up by Bedard – a one-time Baltimore Orioles standout – might not seem extraordinarily high, but consider that the southpaw posted a career-worst 5.01 ERA in 2012, so his most recent returns are not impressing anyone.

The Nats have faced tougher competition at home this month, playing a combined 10 games against the 15-8 Atlanta Braves, 14-10 St. Louis Cardinals and 14-12 Cincinnati Reds – winners of Sunday’s series finale at Nationals Park. Nine of the 16 home games featured warmer than normal temperatures, and the Nats scored four or more runs in five of them, or in just slightly more than half of the “warm” games (see the table below).

Similar to the A’s experience, Washington benefited from matchups against subpar pitchers in their higher-scoring games, with only the Chicago White Sox’s Jake Peavy standing out as a pitcher with a relatively low ERA (3.46). Perhaps Peavy and his career 4-5 record (3.87 ERA) versus the Nats was his undoing in that April 9 contest, in which the 12-year veteran surrendered six runs in 5 1/3 innings.

April 2013 home game log for the Washington Nationals. Above normal temperature departures are bolded in red, while below normal departures are bolded in blue. Three or fewer runs scored by the A’s are bolded in blue; four or more runs are bolded in red.

Even with the increased production against lackluster pitching, Washington – aside from the three-game series against Chicago – is not putting up consistently big numbers on offense. Several of the everyday starters are scuffling at the plate, with Adam LaRoche’s travails drawing the most attention. As it turns out, the slow start is actually habitual for many of the eight starting position players.

Batting averages for members of the Nats’ everyday lineup. Bryce Harper is far outpacing his career numbers, while LaRoche is slumping mightily.

Four of the biggest run producers on the club – Jayson Werth, Ryan Zimmerman, Adam LaRoche and Ian Desmond – historically hit for a batting average (calculated by dividing the player’s number of hits by his number of at bats) in April that’s lower than their career batting average.

If it seems like a big name is missing from this analysis, it most assuredly is. Bryce Harper – he of the towering home runs audacious steals of home base, and major league eye black – is raking exceptionally well in April, outhitting his career batting average of .279 by 81 points (.360) and his career April average (including his time spent in the minors in 2011) of .286 by 74 points.

The weather may have been cool at times in April, but Harper’s one of the few Nats who has kept his cool at the plate. Maybe Harper can show Oakland – recent losers of three of four games to the Orioles – the meaning of a real hot streak when the Nats and A’s meet in the World Series …

All statistics provided by Baseball-Reference.com, FanGraphs, ESPN.com, and MLB.com.