Even in a winter in which the surreal has been the rule, this forecast has hallucinatory qualities.

It calls for yet another mega-snowstorm, a foot-plus, maybe up to 20 inches, more than enough to make this the snowiest winter on record in Philadelphia history.

"People think this is unusual. It is," said Paul Kocin, a winter-storm specialist. He is a meteorologist at National Weather Service headquarters, outside snowbound Washington, where white houses are everywhere these days.

As unbelievable as it might seem, meteorologically, at least, the storm that will affect the area tomorrow night through Wednesday might be more potent than the weekend 2-foot special.

"This one, actually in terms of intensification, is going to make the last one look like a baby," Kocin said.

If even the low end of the accumulation forecast works out, this would become the snowiest winter in Philadelphia history. The current seasonal total is 56.3 and gaining rapidly on the reigning champ, 1995-96, in the clubhouse at 65.5.

"It's incredible," said Tony Gigi, a meteorologist at the National Weather Service office in Mount Holly. "I never would have thought I would see another '95-96. This is going to leave '95-96 in the dust . . . I mean, in the drifts."

Philadelphia already has had an unprecedented two 2-foot snowstorms this winter, and never in records dating to 1884 have back-to-back whoppers hit within a few days.

Three monster storms did affect the region within a week in January 1978 with 7 inches of precipitation - the equivalent of 6 feet of snow - but only one of those was all snow.

Typically, the atmosphere likes to catch its breath.

"One of the big storms kind of takes the energy out of the balloon," Kocin said.

In this case, however, the weekend storm peaked here, "and then it kind of faded away," he said. "It didn't change the dynamic and overwhelm the circulation."

As to why the storms keep targeting the Washington-Philadelphia corridor, Kocin says he believes it has to do with unusually higher air pressures to the north that have allowed cold air to plunge southward.

Storms tend to form along the boundaries of warm and cold air - the temperature "gradient" - and that boundary has been displaced well south of usual this winter.

"What this pattern does is shift everything out of whack," he said.

Since the cold air is plunging so far south, it is encountering unusually warm air. This is giving storms an extra kick: The bigger the temperature contrast, the bigger the potential storm. That will be in evidence the next two days.

"This one is going to be a big bomb," Kocin said.

After this, the storm traffic should slow down, or at least divert elsewhere.

Said Kocin: "This next one should be the last for a while."