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Pittsburgh's Heinz Field will host the NHL's Winter Classic game on Saturday. ((Keith Srakocic/Associated Press))

The weather is becoming a worry for the Winter Classic.

Rain showers and temperatures around 11 C are being forecast for the Capitals-Penguins outdoor game Saturday at Heinz Field (CBC, CBCSports.ca, 12:30 p.m. ET). Those are hardly the conditions the NHL wants for its midseason showcase featuring stars Sidney Crosby and Alex Ovechkin.

While temperatures above freezing aren't ideal, NHL ice chief Dan Craig said they wouldn't necessarily affect a seven centimetre thick ice surface that is refrigerated to -5 C. Only bright sunshine in conjunction with warming temperatures would soften the ice.

Rain is the major worry because it would unsafe for the players even if it falls only lightly. A light rain could freeze almost immediately after hitting the ice, creating an uneven surface that could quickly become unplayable. A steadier rain is even worse because it might flood the surface.

Accuweather, based in State College, Pa., is calling for showers with a high of 11 C on Saturday. The National Weather Service's forecast is nearly identical, except with a high of 12 C. The Weather Channel is predicting temperatures around 9 C and a chance of rain.

While the game is set to start at 1 p.m. ET, it could be pushed back to later in the day if improved conditions are expected.

The forecast Sunday is more favourable, but the NHL prefers not to postpone the game because it then would compete against NFL games for viewers — including the Steelers' game in Cleveland. The Steelers must win that game, or the Ravens must lose at home to Cincinnati, to claim the AFC North title and be seeded No. 2 in the AFC playoffs.

Accuweather's forecast for Sunday is snow flurries with a high of 3 C. The Weather Channel predicts a high of 3 C with rain or snow showers.

Until now, the Winter Classic has been played in near ideal conditions. It was brisk and cold for last season's game in Boston and the 2009 game in Chicago, and the Jan. 1, 2008, game in Buffalo between the Penguins and Sabres was played in a light snow that resulted in a snow-globe effect for spectators and television viewers.

Craig, the NHL operations facilities manager, said the ice maintenance process is more sophisticated than it was for the first Winter Classic. That means the ice can handle more extreme temperatures.

"We have instrumentation that we put into the system called Eye on the Ice that we monitor; (it) sends us signals all the time," Craig said. "Every 15 minutes we'll log and trend it so we can graph what's happening on any given day.

"And every city we go to, we have a complete weather breakdown of our area so we know what (weather) systems are coming through."

The Winter Classic rink has been finished on top of a platform above Heinz Field's grass turf, and icemaking began Sunday. The ice was to be painted white Monday, and the rink markings and logos are to be painted Tuesday. The ice is expected to mature by Thursday, when any final adjustments are to be made.

The ice will first be used for a Capitals-Penguins alumni game featuring Mario Lemieux on Friday morning. The Penguins and Capitals then will practise, although only the Pittsburgh practice is open to the public. Friday's forecast is for milder conditions with clouds, some sun and a high of 9 C.

Saturday and Sunday are the only days the Winter Classic can be played because the stadium must be turned back over to the Steelers. The turf has to be replaced for the second time this season before any Steelers home playoff game.

If the Winter Classic is not played this weekend, the game would be rescheduled for later this season at Consol Energy Center.