Weather forecaster Donald Marier peered out his window atop the highest terminal at National Airport all day yesterday in search of the sun. Finally, at 5.59 p.m., the full disk slipped through the clouds. It was hanging over the western ridge of Arlington, radiating a bright orange.

"As soon as it became visible, I began counting," said Marier."It remained in sight for a total of 11 minutes, beautiful 11 minutes. You should have seen it. It was the best 11 minutes of the day."

The rest of the day was not beautiful. It was dark, f gloomy and wet.

The rains came before dawn, at 4.45 a.m., and continued for 12 hours. Marier counted the minutes of rain, too, because that is his job. It totaled 716 minutes. It also totaled .44 inches at the airport, 1.5 inches in Richmond.

In Marlow Heights another forecaster, Jack Fuge, spent the afternoon watching the thermometer. "It moved up to 44 late in the day," said Fuge. "We were all pushing for 45, but the darn thing doesn't look like it's going to make it."

The winter of 1978 has been one of small victories, modest /hopes. Eleven minutes of sun in early March is a modest hope. A temperature of 45 is a small victory.

But today, at the start of the weekend, there was the promise of something more. As early as Tuesday forecasters began talking about clear weekend skies with temperatures approaching 60.

It was, apparently, too much to hope for. "Im backing off a bit from those early predictions," said Fuge, lead forecaster for the National Weather Service regional office. "It'll be warmer, but I would'nt make too much of a big deal out of it. There should be sunshine with temperatures around 50. That's nothing above normal, you know."

Normal, as Jack Fuge knows is a matter of context. In the context of this January, February and March, a day that approaches the seasonal norm is, in fact, extraordinary.

So far in March, temperatures have been 10 degrees below normal; in January, 3.1. The accumulated snowfall for the first 69 days of the year totaled 22.7 inches, far more than normal.

Today, then, will be an abnormally normal day. Tomorrow will not. Tomorrow, according to Fuge, promises cooler temperatures - in the 40s - and cloudy skies. By dusk it could be raining, or snowing in the mountains of western Maryland and northwestern Virginia.