(This story, first posted Tuesday, was updated Wednesday morning.)

A former typhoon in the Pacific and a potential tropical storm in the Caribbean may help form a major East Coast weather maker Sunday. The coldest air of the season may then flow in behind it.

Wind-swept heavy rain may sweep through the Mid-Atlantic and Northeast on Sunday. In some areas, flash flooding and damaging winds could occur. Downwind of the Great Lakes, the first snowflakes of the season are possible late Sunday into Monday, particularly in the mountains, as the cold air spills southeastward.

The storm is forecast to develop as the jet stream — the slithering river of high altitude winds — plunges south over eastern North America this weekend. This dip is a see-saw-like response to a massive bulge in the jet stream expected to develop over western North America — thanks in part to former Typhoon Lan.

Lan, which battered Japan on Sunday as a Category 2 typhoon, has transitioned into a powerhouse nontropical storm over the North Pacific Ocean, generating waves up to 60 feet high.

Together with another storm over the central Pacific, whose winds knocked out power to all of Maui Tuesday, the former typhoon is predicted to draw up unusually warm air over western North America through late this week — which will intensify the bulge or ridge in the jet stream over that region.

When the jet stream dives south over eastern North America in response, a strong cold front will plow ahead from the Upper Midwest on Friday toward the East Coast on Sunday. Forecast models suggest a storm could develop along the front near the Mid-Atlantic coast Sunday.

As an added wrinkle, the tropical disturbance in the Caribbean, which may become Tropical Storm Philippe, could get drawn into this storm front — intensifying its wind and rain. However, it is not clear whether the Caribbean disturbance will become a storm or if the jet stream will penetrate far enough south to drag it north.

If a significant storm develops along the East Coast, it will move along very quickly because of the jet stream’s rip-roaring speed of more than 150 mph. While likely to change, some models show the potential for several inches of rain and tropical-storm force wind gusts in parts of the Mid-Atlantic and Northeast.

Obviously, this forecast will need to be refined in the coming days as forecast models get a better handle on exactly how any storm evolves and what areas will be hardest-hit.

In the storm’s wake, the eastern half of the Lower 48 should expect a “heavy-duty Arctic blast,” in the words of Ryan Maue, meteorologist with Weather.us.

Models show temperatures dropping as much as 10 to 20 degrees below normal in the Central Plains on Friday. By early Sunday, Houston could flirt with record-low temperatures in the upper 30s.

The cold will lose some of its intensity heading east, but temperatures about 5 to 10 degrees below normal should reach the East Coast by Monday.

In Washington, highs Monday and Tuesday next week should hold in the 50s.

Especially in the mountains downwind of the Great Lakes, over West Virginia and western Pennsylvania, the air may be cold enough for some wet lake-enhanced snow early Monday.