Snowfall forecast made by the National Weather Service through Friday. (WeatherBell)

A strong storm system swirling across the nation is bringing high-impact weather to a span of the country that’s more than 1,000 miles across. The storm includes springtime severe thunderstorms along with wintry weather and even flooding rains. The expansive weather system will dominate the forecast in the East through at least Thursday.

In Chicago, the forecast is a difficult one. Initially anticipated to miss the storm to the northwest, the Windy City now looks to dodge the heaviest snow just to the southeast. In between, forecasts on Monday had called for a potential six to 10 inches in Chicago, a figure forecasters at the National Weather Service have now sliced in half.

Meanwhile, heavy rains continue in the Southeast on Tuesday as the storm’s moisture pivots to the east, even bringing a chance of some offseason severe weather to the Mid-Atlantic by late Wednesday.

Come Thursday, moderate to heavy snowfall is possible in northern New England before lake-effect snow cranks up over Upstate New York on Friday. Such lake-effect snow squalls are more typical for late fall and early winter, but this year’s mild winter has left large expanses of open water on the Great Lakes, allowing cold winds to pick up moisture and deposit it over land.

The wintry side to this storm

The storm is really a combination of two weather systems — a low that spun up Monday over the central Plains and another moving in from the northern Rockies. The combination of the two will bring a swath of snow from central Missouri to Maine.

The flakes are already flying in Missouri, where up to three inches of snow is anticipated through early Wednesday. Much of Illinois will see at least some light snow by late Tuesday.

A total of two to four inches are possible for most of the Chicago area, with more falling to the southeast of the city, due to drier air encroaching from the northwest. A winter weather advisory is in effect for the city, along with a lake-shore flood warning. The latter warning accounts for gusty onshore winds that will push the cold water of Lake Michigan toward the southwestern shoreline, raising water levels there.

“The winds and large, battering waves combined with record high lake levels will exacerbate already significant beach and shoreline erosion,” said the National Weather Service in Chicago.

Heavier snow will fall across northern Indiana and Michigan, with four to eight inches in the forecast for Detroit. The city is under a winter storm watch, with the onset of precipitation expected late Tuesday, with snow continuing through Wednesday evening. During this period, travel could be significantly slowed there, including at the airport, which is a major hub for Delta Air Lines.

Travel delays are also possible in Toronto, where Environment Canada is estimating five to eight inches could fall by Thursday morning. They do, however, note that “there remains uncertainty regarding the track of the low pressure system responsible for the snow.” Similar amounts are possible in Montreal.

The precipitation shield will then move into New England, where heavy snow in excess of half a foot is possible in interior areas by late Wednesday through Thursday.

After the system departs, cold westerly winds in its wake will allow for lake-effect snow showers to stream off Lake Erie on Friday. East of Lake Ontario, accumulations of more than six inches are possible.

Severe storms also possible

The HRRR model simulates a broken line of strong to locally severe storms and downpours eyeing the Mid Atlantic on Wednesday night. (WeatherBell)

As a cold front advances east along with energy in the upper levels of the atmosphere, there is a risk for a few strong to severe storms late Wednesday in the Mid-Atlantic. This is an unusual cold-season setup that could bear watching, with the greatest risk of severe weather focused to the south of Washington.

Any severe risk will be concurrent with the overhead passage of the center of the low-pressure system, which will be associated with very cold air aloft and strong winds that would encourage air to ascend, cool and condense to form clouds and precipitation.

The missing ingredient in this case is sufficient instability, or the tendency for air to rise sufficiently to yield towering storm clouds. With temperatures only in the 50s, instability may be hard to come by. Once in a while, though, strong winds above the ground can help overcome that limiting factor.

Once in a while, sneaky severe events can materialize during out-of-season setups like this, as was the case on Feb. 7, when five tornadoes spun up in the D.C. area on a day that was not forecast to feature any thunder.

This time around, the tornado risk is lower, and the Richmond-to-D.C. corridor could see a few downpours, including some thunderstorms, with a risk of gusty to locally damaging winds. The time frame to watch is between 7 p.m. and midnight on Wednesday.