The major winter storm expected to plaster eastern New England with snow this weekend will first take a pass through the Mid-Atlantic on Friday afternoon and night. It will be in its formative stages but has a chance to generate enough snow for some accumulation and slick roads.

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       Nor’easter could wallop New England with heavy snow and wind Saturday

       Computer models suggest some light snow could develop Friday afternoon along a cold front sliding in from the west. Temperatures initially will be too high for snow to stick, probably in the mid-30s, especially along and east of Interstate 95.

       The question becomes how long snow might last into Friday night and Saturday, when temperatures are projected to drop below freezing. At the moment, the majority of models show snow continuing at least through Friday evening’s commute, when some accumulation could occur and roads could become slippery.

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       Models differ on how long the snow will persist beyond Friday evening. Some indicate much of the snow will end by late Friday, while others keep it going into Saturday afternoon.

       At the moment, we would plan for at least some snow accumulation Friday evening — maybe an inch or two — while anything after that will depend on the track of the coastal storm and how quickly it intensifies.

       Here is our current projection for different snow amounts in the District:

       Chance of at least 1 inch: 40 percent. Chance of at least 3 inches: 20 percent. Chance of at least 6 inches: 10 percent.

       These probabilities are conservative compared with certain model projections but reflect that the storm is still three days away.

       Amounts through Friday evening will probably be greatest in our colder areas north and west of the District. But the heaviest snowfall after that (into Saturday) may well concentrate east of I-95, especially toward the Delmarva Peninsula as the coastal storm gets cranking.

       Discussion

       The four major international modeling systems all simulate at least light snowfall for the region Friday afternoon into Friday night. But some simulations show the snow persisting a lot longer and accumulating a lot more.

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       The amount of snow we see will depend on two primary factors:

       1) The strength of an upper-level disturbance (and associated cold front) passing through Friday.

       2) How fast the coastal storm develops and how close to the coast.

       If a strong upper-level disturbance passes through and the coastal storm develops quickly and close to the coast, we could see substantial snowfall. But if the disturbance is weaker and the coastal storm is slow to develop and passes far offshore, little snow will materialize.

       The European model projects the former scenario and significant amounts of snow along and especially east of I-95. The snow continues through Friday night and doesn’t taper off until Saturday afternoon. It slams the Delmarva with a massive snowstorm, with accumulations exceeding a foot and howling winds.

       “It’s a possible scenario but not a likely one,” said Wes Junker, Capital Weather Gang’s winter weather expert.

       Junker said the European model’s projected snowfall seems on the high side given its forecast for the position of the storm, more than 100 miles east of the Delmarva. But he was impressed by the strength of its predicted upper-level disturbance, which he said could produce moderate accumulations if the model is correct.

       The American (GFS), UKMet and Canadian models all suggest less extreme scenarios.

       Here’s how much snow the various models project for the District:

       European: Around 6 inches from primary model | From its group of simulations: Chance of at least 1 inch: 75 percent | Chance of at least 3 inches: 50 percent | Chance of at least 6 inches: 25 percent. American: 3 to 4 inches from primary model | From its group of simulations: Chance of at least 1 inch: 55 percent | Chance of at least 3 inches: 20 percent | Chance of at least 6 inches: 0 percent. Canadian: Around 3 inches from primary model | From its group of simulations: Chance of at least 1 inch: 60 percent | Chance of at least 3 inches: 10 percent | Chance of at least 6 inches: 0 percent. UKMet: Around 1 inch from primary model.

       We’ll attempt to refine this forecast over the next few days.