The start of tornado season was late but deadly, and now severe weather with the potential for twisters threatens parts of the Plains and Midwest -- including major cities -- heading into the weekend, forecasters said.

Severe thunderstorms looked likely to build over the Plains through the weekend and into Monday. There is some chance of tornadoes developing, the channel said, as moist air from the Gulf of Mexico meets a jet stream moving eastward from the Rocky Mountains.

Late afternoon thunderstorms were expected to move in over Oklahoma City and Kansas City on Sunday, Weather Channel meteorologist Michael Palmer said. More severe thunderstorms were predicted to build over St. Louis and Springfield, Mo. on Monday, he reported.

As many as 16 tornadoes struck northern Texas on Wednesday evening, leveling homes in the towns of Granbury and Cleburne and claiming the lives of six adults. One of the twisters was preliminarily classified EF-4 by the National Weather Service, meaning its winds reached speeds of 160 to 200 miles per hour.

Overall, tornadic activity has been slow this May, typically the month when twisters do some of their worst damage, said the Weather Channel’s Tom Moore.

“We’ve had a shortened season, so to speak,” Moore said, mostly due to blasts of cold air that brought a late chill to central parts of the country.

Any twisters that develop over the Plains on Saturday are likely to form in remote regions, but the foul weather could move closer to cities on Sunday, covering a wide swath from Oklahoma City and Tulsa to Joplin, Mo., and Springfield, Mo.

“I suspect that there will be some tornadoes on Sunday,” Moore said. “There’s a slight chance it could grow a little bit of a tail, that it could get down to Dallas and Fort Worth.”

Hail as large as two inches in diameter could fall from northwestern parts of Oklahoma to North Dakota on Saturday, moving into Kansas, Missouri, and Minnesota on Sunday, the Weather Channel said. The severe weather was slow moving but expected to head further eastward into the later part of next week.

Related:

• 'I couldn't stop screaming': Witnesses describe Texas tornadoes
• Search for Texas tornado survivors: Some victims 'not even near their homes'
• Texas tornadoes devastate neighborhood built by residents, Habitat for Humanity

Terry Prather / AP

Snow falls early Sunday, March 17, 2013, as an Amish family travels to church services near Maysville, Ky.

A pair of storm systems that were moving across the country on Sunday could join forces to bring snow to the Northeast — even as the official start of spring approaches next week.

One storm was spreading snow showers from the Cascades and northern Rockies into the northern Plains and was expected to bring snow to the Dakotas, Minnesota and western Wisconsin tonight, the Weather Channel said.

There was also a chance of snow in West Virgina, southwest Pennsylvania and northwestern Virginia Sunday night, according to meteorologists.

Another storm system was moving over the Ohio Valley Sunday and was expected to continue moving east, joining the northern system to produce a "fairly potent storm off the New England coast Tuesday," the Weather Channel said.

In addition, severe thunderstorms were in Monday's forecast from southern Ohio down into Kentucky, Tennessee and parts of Alabama, Mississippi, Louisiana and northeast Texas.

Snow was expected to close in on parts of the Northeast as the work week gets underway. The Weather Channel said the best chance for accumulating snow and freezing rain was in New England and other interior sections of the Northeast.

Snow is also possible on the I-95 corridor from Washington to Philadelphia Sunday night and from New York to Boston Monday night.

The National Oceanic and Atmosphere Administration called for a chance of rain in New York City Monday, with showers also forecast for Tuesday. NOAA also forecasted snow early Tuesday morning in Boston, but little accumulation is expected as the precipitation turns to sleet and rain during the day.

Wednesday marks the first official day of spring.

Published at 6:05 a.m. ET: A winter storm heading for the Northeast could bring major snowfall to upstate New York and New England on Friday and into the weekend – but forecasts are divided on its potential impact.

A clipper from the north is expected to combine with a rainy storm moving through the South to create a snowstorm for many parts of the region late Friday and Saturday, according to Weather Channel meteorologist Kevin Roth.

However, there is still some uncertainty on exactly where and when the two systems combine, he said.

For cities such as Boston, the changing forecast could mean the difference between an icy nuisance and a major winter storm that would dump up to 2 feet of snow, bringing widespread disruption.

“The European model, which is the generally the best model we have, has continued to insist there is going to be this really big storm but the other models are not bullish on it at all,” the Weather Channel’s Carl Parker said. “The difference is -- will it be a blockbuster for places like Boston?” 

The last time Boston had one foot of snow was in January 2011.

Most of the I-95 corridor is already set for heavy rain on Friday.

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Under the European model, the whole region would see significant snow but up to 2 feet would be dumped on Massachusetts – including Boston – and southern Maine overnight Friday.

That level of snow is “potentially life-threatening,” the Weather Channel’s Chris Warren warned.

However, other U.S. models show the two systems combining further to the east, meaning there would still be heavy snow in northern New England but cities such as Boston could receive as little as 2 inches.

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