PHILADELPHIA — Computer models continue to insist with a rather uncharacteristic certainty that the Philadelphia region and much of the Mid-Atlantic can expect a significant snowstorm during the weekend.

Now, when have they ever been wrong?

On Wednesday, models were in general agreement that Philly had a high likelihood of a snowfall of at least 6 inches, the National Weather Service said, with the potential for substantially more. It listed Sunday’s snow probability at 80%, unusually high for an event at least four days away.

Whatever does or does not happen from here, the likes of Acme, Giant, Wegmans, Whole Foods, and Trader Joe’s thank you.

“All the tools we have are starting to point toward something is going to happen,” said Mike Lee, a lead meteorologist at the weather service office in Mount Holly.

“We know it’s going to get more people uneasy, but we want people to be aware.”

It’s too early to make a guess on snow totals, his colleague, Alex Staarmann said.

“We’re definitely going to get some snow. It could be a significant storm for most of the region. That’s all we can say at this point.”

He added that it wouldn’t melt quickly with temperatures remaining below freezing for several days. Wind chills Monday night could fall below zero, he said.

As for the chances that snow will snub the region this weekend (it’s been known to happen), Bob Oravec, lead forecaster with the National Oceanic and Atmospheric Administration’s Weather Prediction Center, said that’s highly unlikely. “Given the very good agreement in the numerical models, this has a very low chance of being a bust overall.”

Early estimates for snow amounts vary from the prodigious to the prosaic.

The big commercial services, AccuWeather Inc. and the Weather Channel, also are on board. In fact, although the storm remains a virtual concept, the Weather Channel already has affixed a name to it.

When might snow arrive in the Philly area?

Forecasters said the snow could begin as early as late Saturday, and continue into Monday.

The snow would spread south to north.

In the early going, it was uncertain which areas would receive the very heftiest amounts.

The snow machine would be set off by dry polar air interacting with copious moisture to the south, which is likely to encounter resistance to the north.

The big snows would occur between that dry wall to the north and a wall of ice and rain to the south, said Matt Benz, a senior meteorologist with AccuWeather.

Whatever does fall in Philly likely would all snow, but it’s possible sleet could mix in south of the city.

After temperatures moderate the next two days and climb into the mid-40s Thursday, the cold air is expected to pour into the region Friday. High temperatures Saturday through Monday may struggle to get past 20, with or without a snow cover.

Is it possible that Philly will be flakeless?

Of course.

Snow forecast busts are part of the cost of doing winter business in the Philly region.

Some of the key west-to-east moving features that will power the system have not yet made landfall, and thus have not been observed by land-based instruments.

One piece of energy is over the Pacific, and another somewhere over Siberia, Benz said.

“The pieces just aren’t moving that quickly,” he said. They may not make landfall over North America until Thursday, he added, and that could be present real issues for the machines and their human interpreters.

Said Oravec: “Historically, when these features can better be identified by the weather balloon network across North America, the models forecasts improve and converge on a common solution.”

Benz said it may take until Friday for computers to sort it all out with newly ingested data.

Recall that the snow forecasts last weekend bedeviled forecasters on both Saturday and Sunday.

Oravec said computer models are marvels and “do a great job at identifying large-scale patterns that are conducive for major winter storms.”

But “some of the smaller details that can enhance the impacts are harder to model.”

Perhaps the most important data point to consider: The prospective first flakes may not be in evidence until the very beginning of next week.

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